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1 EVALUATION OF SUMMER COVER CROPS SORGHUM SUDANGRASS ( SORGHUM BICOLOR L. ( MOENCH ) X SORGHUM SUDANENSE ) AND PIGEON PEA ( C AJANUS CAJAN L.) MANAGEMENT ON FALL C ABBAGE By DAKSON SANON A THESIS PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE UNIVERSITY OF FLORIDA 2013
2 2013 Dakson Sanon
3 To my Mom and my daughter Daknishael Bezaleel
4 A CKNOWLEDGMENTS I wish above all to thank God for giving me health, strength and courage to achieve this important journey in my life. My deepest gratitude goes to my major professor, Dr. Danielle D. Treadwell for all of her help over the past two years. Sh e has not only guided me through my research and my writing but also allowed me to grow socially, academically, and professionally. My sincere thanks go as well to the members of my advisory committee, Dr. Oscar E. Liburd and Dr. Lincoln Zotarelli for thei r assistance, technical support, and guidance. I would particularly like to thank Mike Alligood and Dr. Teresia W. Nyoike, for they have given me a great deal of help through this process. I would also like to thank the United States Agency for Internatio nal Development /Watershed Initiative for National Natural Environmental Resources ( USAID/WINNER ) Project for granting a scholarship for my graduate program at the University of Florida I would like to thank University of Florida /Institute of Food and Ag ricultural Sciences (UF IFAS) International office staff members, Florence Sergile, Dr. Walter Bowen, Jennifer Holloran, Shary Arnold, and Melissa Wokasch for their support. I also thank WINNER Project staff Members in Haiti, Dr. Jean Robert Estime and Mari e Claude Vorbe. I want to thank Dr. Liburd laboratory members for their assistance in identifying and counting insects. Thanks also to Dr. Steve A. Sargent fo r helping with the microscope in his laboratory. I would like to tha nk my friends and colleagues Lilian Mpinga, Reginald Toussaint, Winjing Guan, Lidwine Hypolite, Marie Pascale Francois, Joseph Beneche, Libby Rens, Allisson L. Beyer, Lyn Max, Desire, Mildred, Seth, Maggie Golman, Ronald Cademus, Lemane Delva, Marie Solaine Leogene Dorestant, and Leju in Brutus for their
5 help. My sincere thanks go to the UF/IFAS expe rimental field crew in Live Oak including; Jerry Butler, Randi Randell, and Wanda Laughlin for always be ing glad and ready to help. I am deeply indebted to my family members for constantly s upporting me during every moment of my Master program. Knowing that the heart can feel what the mouth has forgotten to say, may everyone who one way or another contributed to this achievement find here the expression of my sincere thanks.
6 TABLE OF CONT ENTS page ACKNOWLEDGMENTS ................................ ................................ ................................ .. 4 LIST OF TABLES ................................ ................................ ................................ ............ 8 LIST OF FIGURES ................................ ................................ ................................ ........ 10 ABSTRACT ................................ ................................ ................................ ................... 11 CHAPTER 1 INTRODUCTION ................................ ................................ ................................ .... 13 Cover Crops ................................ ................................ ................................ ............ 16 Pigeon Pea as a Cover Crop ................................ ................................ ............ 18 Sorghum Sudangrass as a Cover Crop ................................ ............................ 20 Cover Crop Mixtures ................................ ................................ ........................ 22 Cover Crop Management System for Vegetable Production ................................ .. 23 Cover Crops in Integrated Pest Management (IPM) ................................ ............... 24 Key Pests in Cabbage ................................ ................................ ............................ 26 Cabbage Production and Management ................................ ................................ .. 30 Conclusions ................................ ................................ ................................ ............ 33 2 CABBAGE RESPONSE TO PIGEON PEA AND SORGHUM SUDANGRASS COVER CROP FERTILTY AND RESIDUE MANAGEMENT ................................ .. 35 Materials and Methods ................................ ................................ ............................ 38 Experimental Site ................................ ................................ ............................. 38 Experimental Design ................................ ................................ ........................ 39 Cover Crop Management ................................ ................................ ................. 40 Cabbage Management ................................ ................................ ..................... 40 Data Collection ................................ ................................ ................................ 41 Cover crop biomass ................................ ................................ ................... 41 Soil nutrients ................................ ................................ .............................. 42 Weed biomass in transplanted cabbage ................................ .................... 42 Cabbage yield and yield parameters ................................ .......................... 43 Statistical Analysis ................................ ................................ ............................ 43 Results and Discussion ................................ ................................ ........................... 43 Weather conditions ................................ ................................ ........................... 43 Soil Nitrogen (nitrate) ................................ ................................ ....................... 44 Effect of Fertilizer on Cover Crop and Weed Biomass ................................ ..... 44 Cover crop biomass ................................ ................................ ................... 44 Weed biomass at cover crop termination ................................ ................... 45 Weed biomass during cabbage production ................................ ................ 46 Cabbage Yield and Yield Parameters ................................ .............................. 47
7 Interaction Effects on Cabbage Yield and Yield Parameters ............................ 48 Yield Parameters ................................ ................................ .............................. 50 Fall 2012 ................................ ................................ ................................ .... 50 Cover crop x cover crop termination methods interaction effect on MH ..... 51 Cover crop x fertilizer x C TM interaction effects on TY, PHW, and WW .... 51 Cover crop x fertilizer x CTM interaction effects on yield parameters ........ 52 Conclusions ................................ ................................ ................................ ............ 52 3 PIGEON PEA AND SORGHUM SUDANGRASS MANAGEMENT CHANGES THE POPULATION OF PEST AND BENEFICIAL INSECTS IN CABBAGE. .......... 75 Materials and Methods ................................ ................................ ............................ 78 Experimental Site ................................ ................................ ............................. 78 Experimental Design ................................ ................................ ........................ 78 Cover Cr op Management ................................ ................................ ................. 79 Cabbage Management ................................ ................................ ..................... 79 Data Collection ................................ ................................ ................................ 81 Statistic al Analysis ................................ ................................ ............................ 82 Results and Discussion ................................ ................................ ........................... 82 Effect of Cover Crops and Tillage on Insect Populations from Pitfall Traps ..... 82 Effect of Fertilizer and Tillage on GB and FA Populations ................................ 83 Effect of Cover Crops and Tillage on Insect Populations from YST ................. 84 Effect of Cover Crops and Tillage on Insect Populations from in Situ Count .... 85 Conclusions ................................ ................................ ................................ ............ 87 4 CONCLUSIONS ................................ ................................ ................................ ..... 99 LIST OF REFERENCES ................................ ................................ ............................. 102 BIOGRAPHICAL SKETCH ................................ ................................ .......................... 114
8 LIST OF TABLES Ta ble page 2 1 Cover crops repartition and seeding rate establishment for summer 2011 and 2012 growing seasons in Live Oak Florida ................................ ......................... 55 2 2 Main effect treatments arrangement according to the experimental design established during growing season 2011 and 2012 in Live Oak Florida. ............ 56 2 3 Soil chemical properties (0 15 cm depth) of the experimental site in Live Oak Florida during fall 2011 and 2012. ................................ ................................ ...... 58 2 4 Analysis of variance summary for cover for cover crop dry weight, weed dry weight, cabbage yield as a ffe cted by cover crop planting fertilizer, and CTM .. 59 2 5 I nteraction effects of CC spec ies and fertilizer on CC dry weight in g.m 1 dried at 70 o C for 48 hours.. ................................ ................................ ................ 61 2 6 Interaction effects of cover crop species and fertilizer on weed dry weight in g.m 1 dried at 70 o C for 48 hours. ................................ ................................ ...... 62 2 7 Interaction effects of cover crop species and fertilizer on weed dry weight in g.m 1 dried at 70 o C for 48 hours. ................................ ................................ ...... 63 2 8 Effects of cover crops, fertilizer, and tillage on weed dry weight in cabbage (Brassica oleracea cv Bravo). ................................ ................................ ............ 64 2 9 Interaction effects of fertilizer and cover crop termination method; cover crop species and CTM on weed dry weight in Live Oak Florida. ................................ 65 2 10 Interaction effects of cover crop species and cover crop termination method on cabbage total yield and percent of head weight at harvest ............................ 66 2 11 Interaction effec ts of cover crop species and cover crop termination method on cabbage wrapper leaf and marketable head at harvest ................................ 67 2 12 Interaction effects of cover crop species and cover crop termination m ethod on cabbage head diameter and head height at harvest ................................ ..... 68 2 13 Interaction effects of cover crop species and cover crop termination method on cabbage head core width at harvest in fall 201 1 in Live Oak, Florida. .......... 69 2 14 Interaction effects of fertilized cover crop residues and cover crop termination method on cabbage yields and yield parameters at harvest .............................. 70 2 15 Interaction effects of fertilized cover crop residues and cover crop termination method on cabbage wrapper leaf weight and marketable yield at harvest ........ 71
9 2 16 Interaction effects of cover crop species, fertilizer, and tillage on cabbage head diameter, head height, and head core width at harvest in fall 2012 ........... 72 2 17 Interaction effect s of cover crop species, fertilizer, and tillage on cabbage head diameter, head height, and head core width at harvest ............................. 73 3 1 Cover crops repartition and seeding rate establishment for summer 2011 and 2012 growing seasons in Live Oak Florida ................................ ......................... 89 3 2 Main effect treatments arrangement according to the experimental design established during growing season 2011 and 2012 in Live Oak Flor ida. ............ 91 3 3 Analysis of variance summary for beneficial and insect pest populations as affected by cover crops mulches, fertilizer and tillage ................................ ........ 94 3 4 Effect of Cover crops, fertilizer, and tillage on insect pest and beneficial populations captured in cabbage from passive pitfall traps ................................ 95 3 5 Effect of fertilizer, and till age on ground beetles and fire ants populations captured in cabbage from passive pitfall traps during fall 2011 and 2012 .......... 96 3 6 Effect of Cover crops, fertilizer, and tillage on insect pest and beneficial populations captured in cabbage from active yellow sticky traps ....................... 97 3 7 Effect of Cover crops, fertilizer, and tillage on insect pest and beneficial populations captured in cabbage f rom in situ count during fall 2011 and 2012. 98
10 LIST OF FIGURES Figure page 2 1 Monthly air temperature at a height of 60 cm, relative humidity, and rainfall at a height of 2m ................................ ................................ ................................ ... 54 2 2 Sketch of the split split plot design of the experiment laid out in Live Oak, Florida ................................ ................................ ................................ ................ 57 2 3 View of the experiment before and at cover crop (CC) termination.. .................. 60 2 4 Cabbage pictures collected at harvest for fall 2012 in Live Oak, Florida. ......... 74 3 1 Sketch of the split split plot design of the experiment laid out in Live Oak, Florida ................................ ................................ ................................ ................ 90 3 2 Sampling methods used during the experiment for both years. .......................... 92 3 3 A) Stand point where systematic visual counting had lieu every other week; B) Gridded used to count aphids on unbaited yellow sticky traps. ...................... 93
11 Abstract of Thesis Presented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Master of Science EVALUATION OF SUMMER COVER CROPS SORGHUM SUDANGRASS ( SORGHUM BICOLOR L. ( MOENCH ) X SORGHUM SUDANEN SE ) AND PIGEON PEA ( C AJANUS CAJAN L.) MANAGEMENT ON FALL C ABBAGE By Dakson Sanon May 2013 Chair: Danielle D. Treadwell Major: Horticultural Science This two year experiment had two objectives. The first objective was to identify the cover crop planting arrangement and tillage method that resulted in the greatest cabbage yield in tropical and subtropical environment by evaluating two different summer cover crops. The second objective consisted of investigating the effect of this two summer cover crops pl anting arrangement and tillage on management of key pest and beneficial insects in cabbage, Brassica oleracea var. Capitata used as a test crop. The experiment was conducted in Live Oak, Florida at the UF IFAS North Florida Research and Education Center Su wannee Valley in fall 2011 and was repeated in fall 2012. Treatments were arranged in a split split plot design and replicated four times. Main effects included four cover crop (CC) treatments: pigeon pea (PP); sorghum Sudangrass (SS); PP and SS bicultur e (SP); and no cover crop (control). Cover crop plots were equally split in week four after CC emergence with two levels of nitrogen (N): 57 kg ha 1 or 0 kg ha 1 (subplots). Each subplot was equally split again prior to cabbage transplanting. Cover crops w ere mowed and soil incorporated (CT) or rolled (NT) with a
12 roller crimper (sub subplots). Data were collected on CC biomass, weed biomass, cabbage yield and yield parameters, key pests on cabbage including ; and beneficial insects using yellow sticky cards, pitfall traps and foliar counts. Measured cabbage total and marketable yields were greater in fall 2011 than fall 2012. The greatest cabbage yield and marketable yield were 54 and 38 ton.ha 1 respectively in fall 2011 and 38 and 17 ton.ha 1 respectively in fall 2012. Yields obtained in general from CT plots were yield were consistently greater in PP plots in both years. Aphid populations were significant within most o f the treatment s in both years except in PP main effect treatments. DBM was not significant in any treatment in both years. Whi tefly population was lowest in SS main effect treatments. Among the most common beneficial insects, ground beetles, spiders and fire ants, wasps and syrphid flies were significantly more abundant during both cabbage growing seasons
13 CHAPTER 1 INTRODUCTION For ages worldwide agriculture has experienced serious changes and consequently has become more and more fragile in terms of sustainability. This situation has sparked the necessity for new strategies by researchers and farmers to cultivate the soil to alleviate this prominent fragility of current agricultural practices. For example, c oncerns over soil quality degradation have g iven rise to the development of conservation tillage during the last five decades Baldwin (2009). Indeed, this cultural practice is more common in vegetable production especially sustainable and organic vegetable production. Conservation tillage presents several economic benefits and opportunities for growers in the United States (U.S) Recent studies suggest that conservation tillage practices can be beneficial to the production of horticultural crops (Hoyt et al., 1994). One of the major components of c onservation tillage systems for vegetable production is cover cropping system s In general, c over crops can reduce soil erosion ( Dabney et al., 2001 ), limit runoff and surface water pollution (Hall et al., 1984), influence soil fertility by providing a sou rce of nitrogen ( N ) for subsequent crops ( Carof et al., 2007; Kuo and Jellum, 2002 ) and capturing soil mineral N to prevent loss to leaching ( Thiessen Martens et al., 2005 ). When rotated into organic production systems, cover crops may also provide alterna tives to chemical inputs for pest management, as they have been demonstrated to suppress weeds (Finney et al., 2009 ; Treadwell et al., 2007), disrupt pest and disease cycle (Hartwig and Ammon, 2002 ; Liburd et al., 2008 ), and suppress nematode populations ( Brainard et al., 2011 ).
14 E xperiments conducted on cover crops have focused more on winter annual species than summer species. Sorghum sudangrass ( Sorghum bicolor L. Moench X Sorghum sudanense ) and pigeon pea ( Cajanus cajan ) as summer cover crop s in conserva tion tillage systems seem to be subject of very few studies D espite that, these S orghum sudangrass as a summer cover crop has the potential to produce abundant biomass (Creamer and Baldwin, 20 00), suppress weeds through physical and chemical interference (Creamer and Baldwin, 2000; Weston et al., 1989) and decrease soil compaction (Wolfe et al., 1998). Sorhum sudangrass is commonly cultivated as a forage crop for grazing, hay, or silage (Chambl ee et al., 1995), and may be suited to cultivate as both cover and hay crop in organic sustainable conservation tillage vegetable production. Sorghum sudangrass can produce allelopat hic chemicals that can disrupt the growth of neighboring plants (Weston et al., 1989) Sorghum sundangrass mulch has been demonstrated to inhibit germination of summer annual weeds including common purslane ( Portulaca oleracea L.), common lambsquaters ( Chenopodium album L.), redroot pigweed ( Amaranthus retroflexus L.) and smooth crabgrass ( Digitaria ischaemum (Sch reb.) Muhl) (Putman and DeFrank, 1983 ). In addition pigeon pea is recognized as cover crop for its potential to produce abundant biomass, prevent nutrient leaching, suppress weeds, fix nitrogen (N) and sequester carbon (Valenzuela, 2011) In terms of N fixation, pigeon peas are nodulated by a wide range of r hizobia strains including Bradyrhizobium sp p (cowpea group). Pigeon peas are considered to have greater N fixation rates compared to other legume species (Chikowo e t al., 2004). Nitrogen fixation rates in an African study were
15 estimated to range from 40 97 kg ha 1 (Mafongoya et al., 2006). Other research results from Africa and India also showed N contributions from pigeon pea to the following crop in the rotation to be in the range of 40 60 kg N ha 1 (Odeny, 2007). In Florida N fixation from pigeon pea was estimated to be 250 kg N ha 1 (Reddy et al., 1986a). Estimates indicate that leaf drops can contribute up to 40 kg N ha 1 to the system (Mafongoya et al., 2006). Pigeon peas develop a deep rooting taproot up to 2 m in depth which helps to break compacted soil layer improve soil water infiltration and percolation and mines nutrients and moisture from the lower soil layers (Mafongoya et al., 2006). The amount of nu trient released from root decomposition amounted to over 40 kg N ha 1 and over 80 kg ha 1 phosphorous, representing a potential valuable pool of nutrient for the following crops in the rotation (Barber and Navarro, 1994). Pigeon peas are used in intercropp ing and multiple cropping systems. In many tropical regions pigeon peas are cultivated in intercropping systems with crop s such as millet or corn. In Hawaii pigeon pea w as interplanted with pineapple to improve soil properties ( Valenzuela 2011). Mulch f rom pigeon pea residues can be effective for weed suppression (Ekeleme et al 2003). As a cover crop, pigeon peas have been used as cover in particular in coffee, corn, and other crops. Benefits of the pigeon pea cover crop includ e improved soil fertilit y, reducing weed competition, and increased arthropod diversity (Odeny, 2007). Some pigeon pea varieties have reported resistance to root knot nematodes, Meloidogyne incognita (Reddy et al., 1986b; Baldwin and Creamer, 2003). Pigeon peas are cultivated as forage as well. They have been evaluated in the South e astern of U.S. for their use as both cover and forage crop, in integrated crop
16 livestock systems (Franzluebbers, 2007). Overall the use of pigeon pea in multiple cropping systems resulted in greater res ource use efficiency, crop productivity, more stable or resilient systems over time and in less economic risks to small farmers in the tropics (Yadav et al, 1998; Waddington et al., 2007). Based upon these findings, conducting an experiment that is taken i nto consideration different planting management of pigeon pea and sorghum sudangrass as cover crops could be significant to evaluate their subsequent effects on vegetable cash crop s planted into their residues that are either left on the soil surface or in corporated into the ground. The general purpose of this research was to identify the best cover crop management strategy suitable for optimizing vegetable production in tropical environments. Specifically, our goals were to investigate the cover crop plan ting arrangement and tillage method that results in the greatest cabbage yield (Chapter 2 ) as well as to monitor the insect population s to determine how the cover crop planting arrangement and tillage method influences key insect pests and beneficial popul ations (Chapter 3 ). Cover Crops Cover crops, as defined by Allison (1968), are crops that are in general grown to protect the soil surface by providing living or dead mulch which is positively enhanced soil fertility, soil physical properties, and nutrien t management. Cover crops are crops including grasses, legumes, forbs, or other herbaceous plants established for seasonal cover and soil conservation purposes (NRCS Minnesota, 2007). Based on the cultivated purpose, cover crops may have several appellatio ns. They may be called:
17 disrupt insect pests; wind cetera. Originally cover crops were introduced into agriculture just to provide soil cover or protection (Allison, 1968) and therefore contribute d to the control of soil erosion, as well as to reduce runoff, improve infiltration, maintain soil moisture, and increase soil tilth (Dabney et al., 2001; Carof et al., 2007; Hoyt et al. 1994; Teasdale 1996; Mohler and Teasdale, 1993). Leguminous cover crops are basically rich in N and most of the time release sufficient amount of N that might replace chemical fertilizer (Thiessen Martens et al., 2005). Both legume and non legume cover crops contribute to scavenging and recycling the surplus of macro and micronutrients from the previous crop and therefore reduce the risk of nutrient leaching or surface run off to water bodies. Many researchers have determined that cover crops con tribute to weed suppression (Daniel C. et al., 2011; Treadwell et al., 2007; Williams et al. 2009), and according to Blackshaw (2001), a lot of cover crop species provide weed suppression both during growth and after termination. Cover crops with plant pa rts containing comparatively high C:N (greater than 20:1) and significant dry weight, such as grass and hard stem legumes, present increased weed control for a longer period of time through the growing season compared to cover crops with low C:N (less or e quals to 20:1) ratios (Cherr et al., 2006). Weed suppression may be maximized by using high
18 residue cover crops capable to provide at least 4,500 kg ha 1 of biomass as ground cover (Balkcom et al., 2007). Cover crops are often attractive ecological habitat s for beneficial insects (Reeves, 1994). Conservation tillage coupled with cover crops allows creating year round such an ambiance leading to interactions between natural enemy and insect pests. Because of this, c over crop management is becoming one of the Integrated Pest Management (IPM) strategies promoting the reduction of pest populations while encouraging beneficial populations in the cropping systems Cover crops also suppress nematode populations (Hill et al., 2006). Another potential benefit of cove r crops is the potential to increase subsequent crop yield. Cover crops may or may not increase yield of subsequent crops (Blanco Canqui et. al., 2012; Olson et al., 2010). Fertilized cover crops have increased weeds suppression and crops yield in celery ( Charles et al., 2006). Practical Farmers of Iowa (PFI) reported that yield of soybeans was increased when planted following winter rye ( Secale cereale L.) cover crop (Carlson and Anderson, 2010). Legume cover crop such as hairy vetch ( Vicia villosa L.) and crimson clover ( Trifolium incarnatum L.) are to a large extent more able to enhance crop yields than grass cover crops such as wheat based on the potentiality of legumes to provide nitrogen to the following crop, reducing therefore required nitrogen input s (Roberts et al., 1998). Charles (2006) showed that in hand weeding farming system on celery, cover crops can successfully improve weed management and yield, entailing reduced fertilizer inputs. Pigeon Pea a s a Cover Crop Pigeon pea, Cajanus cajan L. Mill sp. belongs to Fabaceae family along with soybean ( Glycine max L. ) field bean ( Phaseolus vulgaris L. ), and mungbean ( Vignata
19 radiate L. ). Pigeon pea is a widely grown legume especially on tropics and subtropics. Pigeon pea is a multipurpose legume with a long tradition of cultivation in Hawaii (Valenzuela and Smith, 2002). Pigeon peas appear among the top ten worldwide grown legumes, along with chick peas (Latin name needed for each of these please), broadbeans, peas, lentils, and common beans. Important characteristics of pigeon pea are that they are an excellent source of nitrogen, they are used to improve the soil, they are drought tolerant, they are an efficient nutrient scavenger, pigeon pea is a good forage for animal production systems, and finally pigeon pea is easily integrated in annual production systems (vegetables, herbs, cut flowers and ornamentals) intercropping systems and agroforestry systems. Pigeon pea is well adapted to low soil fertility because of its ability to fix atmospheric N and i ts deep root system (Gauchan et al. 2003). As a drought species, pigeon pea can withstand long term stress during its growth cycle (Sinclair, 2004). Pigeon pea varieties vary in the duration to harvest, ranging from less than 60 days (early varieties) to over 200 days (late varieties). Pigeon pea varieties may be determinate (short) or indeterminate (long) (Mligo and Craufurd, 2007). Pigeon pea blooms under short day conditions. Under long day and cold temperatures, flowering is delayed or does not occur ( Mligo and Craufurd, 2005). Pigeon pea is an excellent weed suppressive crop. Biomass production has been found to be roughly 87.5 tons ha 1 of fresh weight green matter and about 6.25 ton ha 1 of dry matter contributing about 57 kg of N per ton of dry matt er. Pigeon pea is effective at breaking soil compaction due to its deep root system. Pigeon pea develops a taproot that can go deeper than 2m (6ft). In India, pigeon pea in rotation contributed to a
20 reduction of bulk density, an increase in root volume and increase in root weight of the subsequent crop in rotation (Singh et al., 2005). Pigeon pea has the potential of maintaining adequate growth under low P conditions compared to the other crops, for instance, corn and soybeans (Sinclair, 2004). However, Adu Gyamfi (1998) found that the lower soil P levels may reduce N fixation in pigeon pea, more specifically in the short duration varieties. Pigeon pea exudes via its roots several organic acids such as citric, piscidic, and tartaric acid that contribute to m obilizing P in the soil (Sinclair, 2004). The intercropping of pigeon pea with grass species increased P uptake by the companion grass crops (Raghothama, 1999). The development of mychorrhizal associations by pigeon pea enhanced nutrient uptake efficiency (Chickowo et al., 2004). Based on its drought, heat, and low fertility conditions tolerance, pigeon pea could be an important crop or cover crop to alleviate the effects of climate change. Sorghum S udangrass as a Cover C rop Sorghum sudangrass hybrids can produce more organic matter per acre, and at a lower seed cost, than any major cover crop grown in the U.S.A. (Clark, A., 2007; Valenzuela and Smith, 2002). Sorghum sudangrass is a hybrid issued from forage type sorghum and sudangrass. Sorghum in general h as a narrow leaf area, numerous secondary roots, a waxy leaf surface, and other traits that contribute to drought tolerance (Sarrantonio, M., 1994). For best growth, sorghum sudangrass needs good soil fertility and supplemental N inputs (Clark, A., 2007). Sorghum sudangrass can produce up to 4,500 to 5,500 kg ha 1 of dry matter. Creamer and Balwin (2000) reported that sorghum sudangrass suppresses weed through physical and chemical interference. Sogoleone root exudate of sorghums which is active at extremely low concentration in comparison with some
21 synthetic herbicides. Sorghum sudangrass is renowned for being very effective at suppressing annual weeds such as, velvetleaf, large crabgrass, barnyardgrass (E inhelling, and Souze, 1992; Nimbal et al., 1996), green foxtail, smooth pigweed, redroot pigweed, common ragweed, and common purslane (Peet, 1995; Putman and DeFrank, 1983). Sorghum sudangrass is also an important tool in integrated pest management (IPM) p rogram. Planting sorghum sudandgrass in lieu of a host crop can help disrupt the life cycle of a stream of diseases, nematodes and other pests. According to an IPM specialist from Cornell Extension, John Mishanec, the use of sorghum sudangrass helps to con trol nutsedge infestation (personal communication). Soghum sudangrass attracts beneficial insects such as seven spotted lady beetles, Coccinella septempunctata and green lacewings, Chrisopa carnea (University of California CCWG, 1996). Sudangrass can contr ibute to N recycling, up to 210 kg ha 1 This potential for N recycling combined with the subsoiling action of its root systems and its effects on weeds and nematodes make sorghum sudangrass renowned for being able to restore soil fertility. On a low produ cing muck soil in New York where onion yields were registered less than one third of the local average, only one year of a dense planting of sorghum sudangrass restored the soil to an almost similar condition to that of newly cleared land (Jacobs, 1995). S orghum sudangrass was demonstrated to reduce pesticide cost, rejuvenate the soil, and increase the yield of onion in rotation on organic soil (Jacobs, 1995).
22 According to a group of researchers at Cornell University, reported by (Clark, 2007), sorghum suda ngrass was the best cover crop for breaking soil compaction in vegetable fields when planted in summer. Soil compaction slows root expansion, prevent nutrient uptake, stunt plants, retard maturity and increase the incidence of pests and diseases (Wolfe, 19 97). According to Wolfe (1997), slow growing cabbage directly seeded into compacted soil was vulnerable to flea beetle (Latin name of flea beetle) infestations. Sorghum sudangrass in Colorado contributed to enhancing irrigated potato tuber quality and tota l marketable yield ( Delgado, et al. 2007 ). Its use also increased nutrient uptake efficiency on high pH sandy soils ( Delgado, and Lemunyon. 2006). Cover Crop Mixtures Cover crop mixtures are combination s of at least two different cover crop species. For i nstance, planting involving a grass with a legume is a mixture. Mixtures have more benefits because each crop in the mix ed may respond differently to soil, pest and weather conditions according to the S usta inable Agriculture Network (2007). Associations of crops present considerable benefits in production systems. Some of positive impacts of cover crop mixtures are availability of nitrogen in appropriate quantities and ideal moment for following crops, attraction of several different species of beneficial i nsects, and providing adequate soil cover for a longer period of time. Under field conditions, a mixture of sorghum sudangrass and sunn hemp produced more dry weight biomass combined (2410 kg ha 1 ) compared to monoculture dry weight 2010 kg ha 1 for sorghu m and 290 kg ha 1 for sunn hemp. Once soil incorporated, a cover crop mixture that includes a grass and a legume can reduce the high C: N ratio of the grass thus facilitating decomposition of organic matter by bacteria In conjunction with that, Balkon et al. (2007) report ed that a mixture of hairy vetch and rye results in a C : N no
23 more than 25:1 while the C: N for 100% rye is between 30:1 and 66:1. Morse (2001) found that the use of winter rye in combination with hairy vetch terminated by a roller in th e spring was the best combination assessed for production of no till summer broccoli. Similarly, McNeill et al. (2012) also reported that a biculture mixture of sorghum sudangrass and velvet bean ( Macuna pruriens ) harbored a high number of syrphid flies ( S yrphid ae ) which contributed to reducing the aphid population in the subsequent squash ( Cucurbita moschata ) crop. Cover Crop Management System for Vegetable Production In vegetable production, cover crops may be managed either under conservation tillage or conventional tillage. The former is, in general, cover crops or/and crop residues dependent. According to Hebblethwaite (1997), conservation tillage, and in particular no til lage (NT) systems, have become normal method s of crop production for field corn an d soybean in some areas of the US. The use of cover crops in vegetable became frequent with the adoption of NT in vegetable crops in the 1990s. Despite the increase in adoption of NT for vegetable crops, many farmers are still reluctant to practice it espe cially those who cultivate small seeded crops (Morse, 1999). Morse stated that research is still needed to assess NT direct seeded for vegetable crops cultivated in rotation with a good stand and well managed high residue cover crops. The desire for farmer s to reduce chemical weed suppression, produce high value and quality crops in NT agronomic crops (Reeves et al., 1997) and transplanted vegetable crops (Morse,1995) have sparked innovation of improved practices for successful growth and management of cove r crop residues. The use of cover crops in NT systems initially had a unique objective to suppress weeds and reduce surface water runoff. Jointly, researchers and farmers showed that the combination of growing and keeping
24 uniformly distributed high residue covers and appropriate use of preemergence and postemergence herbicides provided better weed suppression than that obtained in conventional tillage systems (Abdul Baki et al., 1997). However, recent research conducted on NT vegetable crops showed that far ming practices can increase crop yield as well. In a study led by Abdul Baki et al. (1997), similar yields were found for fall broccoli planted on residues of forage soybean and foxtail millet than for broccoli cultivated conventionally. Hoyt (1999), resea rched the utilization of tillage and cover crops on vegetable yields, and concluded that yield of income generating crops was dependent on the appropriate selection of cover crop type and the amount of cover crop biomass. Mark and Morse (2007) stated that NT cover crop management optimizes cover crop biomass and soil cover, reduces the time between the cover crop termination and the subsequent vegetable crop planting, and contributes to suppression of annual weeds. Cover Crops in Integrated Pest Management (IPM) The use of cover crops is a cultural tactic that is used in IPM for reducing pest populations while encouraging beneficial insect populations in sustainable cropping systems. According to Liburd et al. (2008), cover crops are a key component of orga nic and sustainable agriculture. Back in 1991, Bugg stated that cover crops can be utilized in many ways for insect management practices. When incorporated with a cash crop, cover crops enhance the natural enemy populations (Liburd et al., 2008; Nyoike and Liburd, 2010). Cover crops have the ability to create resilient and balanced agroecosystems. In balanced ecosystems, insect pests remain in check by their natural enemies ( Sustainable Agriculture Network. 2005 ).
25 Besides its role of preventing soil erosio n, improving soil structure, and enhancing fertility, cover crops manage several pests including weeds, arthropods, nematodes and various other pathogens, cover crops can attract several groups of beneficial livings including natural enemies of insect pest s, pollinators and soil nutrient recyclers. Natural enemies attracted by cover crops that may benefit famers include hoverflies ( Syrphidae ), parasites and/or parasitoids, lady beetles ( Harmonia axyridis Pellas), lacewings ( Chrysoperla sp. ), spiders ( Aranea e ), ants ( Formicidae ), assassin bugs ( Platimeris biguttatus ), minute pirate bugs ( Orius sp. ), ground beetles ( Elaphrus viridis ), and big eyed bugs ( Geocoris sp. ). Insectary plants used as cover crops provide in food (nectar and pollen) that is indispensabl e for the survival, development and reproduction of a number of natural enemies including hoverflies and parasitoids (Hogg et al., 2011). Hogg et al. (2011), proposed seven criteria to consider when choosing cover crops for an IPM program: 1) attractivenes s to beneficial insects; 2) early and long blooming period; 3) low potential to host plant viruses; 4) ability to out compete weeds; 5) low potential to become a weed; 6) low attractiveness to pest species; and 7) low cost of seed and establishment. In Ha waii, IPM research conducted on cover crops to manage beneficial organisms both above and below ground provided useful tools to farmers (Koon Hui Wang, 2012). For instance, buckwheat ( Fagopayum esculentum Moench ) intercropped with zucchini ( Curcubita pepo L.), reduced population densities of whiteflies and aphids, as a result, reducing silver leaf symptoms and aphid transmitted viruses on zucchini (Hooks et al., 1998). Hooks and Johnson (2001) reported that intercropping yellow sweet clover ( Melilotus indic us ) with broccoli ( Brassica oleracea ) reduced the number of
26 imported cabbageworm and cabbage looper on broccoli but did not increase insect pest predation. Later, in 2004, they attested that intercropping involving yellow sweet cover with broccoli increase d the number of spiders that in turn considerably reduced the occurrence of lepidopteran pests on broccoli foliage. Wang et al. (2011) reported a significant increase abundance of soil mesoarthropods such as oribatid, predatory mites, collembola, and isopo ds under a strip till cropping system of sunn hemp and marigold (Latin of marigold). Jointly, McNeill et al. (2012) reported that biculture (mixture) sorghum sudangrass with velvet bean harbored high number of syrphid flies which contributed to lower aphid levels in squash as the subsequent cash crop. Nyoike et al. (2008) showed that the utilization of living mulches in combination with the insecticide imidacloprid lowered the number of whiteflies per leaf on zucchini. Key Pests in Cabbage In cabbage, like any other vegetable crop, insect pests are generally the main pest entity. Worldwide, the greatest insect issue for cabbage growers remains the diamondback moth (DBM), Plutella xylostella Diamondback moth is also known as the first major cabbage insect pe st in the state of Florida (Mossler et al., 2011). Other cabbage major insect pests are cabbage looper, Trichoplusia ni cabbageworm, Hellula rogatalis imported cabbageworm, Artogeia rapae silverleaf whitefly, Bemisia argentifolii, and aphids (turnip aph id, Hyadaphis erysimi ; green peach aphid, Myzus persicae ; cabbage aphid, Brevicoryne brassicae ). Whitefly and aphids are more significant in southern Florida where they are viewed as key pests (Hayslip et al., 1953). Diamondback moth became the main pest i n Florida on cabbage during the course of cabbage producers face annually (Leibee, 1996). Diamondback moth attacks cabbage
27 at all stage of growth. Generally, DBM feedi ng causes many small holes in the leaves, and the size of the feeding holes increases as larvae increase in size. They also feed on developing cabbage heads, resulting in shallow tunnels on the top of the heads. Diamondback moth damage may make the head an d leaves entry points prone to decay by secondary pathogens (Hayslip et al., 1953). From mid winter through the spring, DBM may cause losses of up to 70% when no control is taken (Nuessly et al., 1999). DBM are active at temperatures between 10 o C and 26.7 o C (Hyyslip et al., 1953). The economic thresholds for fresh market cabbage infested by DBM and other early heading to mature head (Foster and Flood, 1995). Cabbage lopper (CL) is also one among the most harmful annual pest for cabbage in Florida. Research on CL showed that adult populations tend to be highest in late spring and summer, and sometimes in the late fall (Nuessly et al., 1999). However, in central Florida, CL p opulations are highest during the course of early fall and late spring (Leibee, 1996). According to Mossler et al. (2011), cabbage looper is generally much more of an issue on Florida cabbage in the fall compared to the winter and spring months. Cabbage lo oper feed on cabbage leaves and developing heads. Research in Texas showed that control is necessary when population densities reach 0.3 larvae per plant (Capinera, 1999a). Establishment of an action threshold of 0.1 medium to large CL larvae per plant was effective In Florida for cabbage (Hayslip et al., 1953; Liebee, 1996). Their life cycle can be achieved at a temperature range between 21 o C and 32 o C (Hayslip et al., 1953; Liebee, 1996).
28 Cabbageworms (CW) as well as imported cabbageworms (ICW) may be cont rolled by treatments similar to that for DBM. Cabbageworms feed on cabbage in seedbeds and in the field (Hayslip et al., 1953). Cabbage head formation can fail and the plant appearance tends to be lopsided following feeding by CW (Hayslip et al., 1953). Im ported cabbage worm produces large holes in leaves and may attack heads up to head fill, causing damage similar to DBM (Workman, 1983). Whitefly (WF) is not known as major pest for cabbage, but it is very frequent on cabbage in southern Florida. Whiteflies extract plant sap by piercing and sucking. They excrete excess liquid in the form of honeydew that can give rise to the growth of sooty mold (Johnson et al., 1996). In a study conducted on zucchini squash, Nyoike et al. (2008) reported that living mulches were effective in reducing densities of WF on zucchini plants. Studies conducted on the evaluation of living mulches on WF and aphids showed a successful reduction in their population densities and a possible delay of the debut and distribution of associa ted insect borne diseases. Aphids are one of the most economically important pests for cruciferous crops in general, and for cabbage in particular. The three aphid species that attack cabbage in Florida include Turnip aphid, ( Hyadaphis erysimi ) ; green peac h aphid ( Myzus persicae ) and cabbage aphid ( Brevicoryne brassicae ) and are among the five more economically important aphid species for cruciferous crops in the U.S. Turnip aphid and green peach aphid remain the most common aphids on cabbage in Florida (We bb, 2003). With low pest density, honeydew and the black sooty mold fungus obtained as a result of their feeding may contaminate the crop and reduce its marketability. However, when population density is high, sooty mold can become very thick and block sun light thus
29 lowering photosynthesis and ultimately reducing yield. Aphid can be protected from insecticide applications within the curled leaves or inside the cupped leaves of cabbage heads (Hayslip et al. 1953 ). Alternatively, many researchers in organic a nd sustainable agriculture stated that cultural practices including use of cover crops contributes to reducing aphid population densities to a tolerable level in cruciferous crops (Wang et al., 2011). There is no scientific based economic threshold establi shed for aphids on any cruciferous crops. However, several empirical action thresholds were determined to evaluate the economic impact of aphid infestation (Liu and Spark Jr., 2001). For some researchers in cabbage, the effect of aphid infestation is more significant at cabbage early stage. Palumbo (2006) reported significant head contamination at a 10% action threshold (10% plants infested with 5 or more aphids) when aphids on cabbage were managed exclusively with reduced risk insecticides. Associated n at ural e nemies of i nsect p ests in c abbage Cover crops are renowned to be able to enhance natural enemy populations when intercropping with a cash crop (Frank and Liburd, 2005; Liburd et al., 2008; Nyoike and Liburd, 2010). The majority of associated natura l enemies of insect pests in vegetable production systems are effective for insect pest management in cabbage as well. These beneficial insects include beneficial arthropods, various parasitoids and predators, predatory wasps, lady beetles, ground beetles, lacewings, spiders, ants, big eyed bugs, damsel bugs, syrphid flies, et cetera. Hooks and Johnson (2004) reported that spiders contributed to considerably reducing lepidopteran pests on broccoli foliage. All stages of the DBM are attacked by a stream of p arasitoids and predators (Reddy et al., 2002). According to Romeis et al. (1997), emission of volatiles by sorghum ( Sorghum bicolor L.) attract and
30 capture Trichogramma chilonis that Muira and Kobayashi (1998) further reported as a particularly effective i n control of DBM. Areneae (Lycosiadae, Clubionidae, Oxyopidae), Coleotera (Carabidae, Coccinelidae, Staphylinidae), Neuroptera (Chrysopidae), and formicidae were the most abundant group of predatory beneficials that were captured in pitfall traps in cabbag e trial and correlated to important mortality of DBM (Furlong et al., 2004. According to Ramirez and Patterson (2011), damsel bugs are generalist predators that consume significant amounts of aphids and caterpillars. Cabbage Production and Management Th e U.S. fresh market cabbage production is consistently led by California, and along with New York, Florida, Texas and Georgia, constituted the top five cabbage producing states in 2011. Florida ranks third in terms of harvested acreage, yield, and market v alue (National Agricultural Statistics Service, 2012). Florida cabbage production and market value were estimated at 350 million kg and $74 million respectively in 2011 (NASS, 2012). According to NASS (2012), the total harvested acreage for the same year w as approximately 3,200 ha. In Florida, cabbage production is occurs during fall. First planting dates for cabbage in Florida are usually between August and March. In north Florida, first planting dates are between August and February, for central Florida b etween September and February, and for south Florida, between September and January (Maynard et al., 2003). Sargent (1999) reported that the maximum quality cabbage was produced during the late fall, winter and early spring months in Florida. This planting cabbage to areas of the U.S. where cabbage cannot be produced economically during that same period of the year.
31 Cabbage development is influenced by climatic hazards. For optimal developme nt, cabbage needs an ideal temperature range from 15 o C to 20 o C (UCDANR, dependent disorder consisting of switching from vegetative growth to reproductive growth) when temperatures exceed 24 o C (Guide to Commercia l Cabbage Production, 1999). Cabbage needs a significant amount of N during the early stage of development (Sanders, 2001). For instance, The University of IFAS) recommends that 25 to 50% of N be ap plied before planting or transplanting unmulched cole crops (Olson et al., 2013). The nitrogen requirement rate for cabbage in Florida is 200 kg ha 1 N (Olson et al., 2013). Westerveld et al. (2002) found that summer cabbage yields were better when N rates ranged between 220 and 260 kg ha 1 compared to the current recommended rate of 170 kg ha 1 N. Legume cover crops can play an important role in contributing to the supply of the early N requirement (Hoyt and Hargrove, 1986). Cover crops are usually used in No tillage (NT) production systems for their potential to control weeds and therefore have sparked the curiosity of a multitude of researchers to initiate the implementation of cover crops in vegetable production systems as a strategy to suppress weeds. T hat tendency also prevails when cover crops are integrated in brassicas, mainly in cabbage and broccoli production systems. In conventional systems, cover crop biomass is usually removed for animal forage purposes before the soil is tilled. In contrast, in NT systems cover crop residues remain as mulch on the soil surface. Previous studies conducted on cover crop effects on cabbage production showed that most of the time results are similar for NT cabbage compared to conventional tillage
32 (CT) management sy stems. In contrast, Knavel and Herron (1981) stated that spring cabbage yields were decreased in NT when compared to CT. Wilhot et al. (1990) attributed cabbage yield reduction to poor plant establishment and impeded crop growth that extended beyond the ef fect of NT production system alone. Although cover crop residues do reduce weed germination and growth, weed control in NT cabbage usually involved the use of pre emergence (PRE) herbicides. Bellinder et al. (1984) found similar yield to cabbage cultivated both under NT and CT systems when weed control methods and PRE were used. Weed management remains the main drawback of implementing of NT cabbage production systems. Therefore, the cover crop type is extremely important when implemented NT cabbage system. For instance, Morse and Seward (1986), corroborated later by Schonbeck et al. (1993), reported that hairy vetch and Austrian winter pea ( Pisum sativum L.) were better residue covers than winter rye for NT cabbage production, this was likely due to N relea sed by the legumes via decomposition of plant residues provided some additional benefit. In contrast, Masiunas et al. (1997) reported that the use of fall seeded winter rye was a more amenable mulch system in NT cabbage for weed management ; also, weed man agement using winter rye in NT system was comparable to that achieved in CT using trifluralin applied PRE. Morse (1999a) conducted research on broccoli and observed yield was greater in a NT cover crop mulch system in comparison to a NT bare soil system. M orse proposed that NT broccoli can be successfully achieved without incorporating herbicides, especially when proper high residue cover crop are correctly killed by flail mowing or rolling and broccoli transplants are appropriately placed and maintained in this uniformly distributed cover crop mulches.
33 Cover crop mixtures as mulches show promise for NT brassica production systems. Morse (2001) found that the use of winter rye in combination with hairy vetch that was rolled in the spring turned out to be th e best combination assessed for production of summer broccoli. However, Morse concluded that NT broccoli yield is inversely correlated with the amount of weed biomass produced. Conclusion s Cover crops are integrated into vegetable production systems for t heir ability to suppress weeds and scavenge nutrients that may be ultimately available to subsequent cash crops. Several researchers have attempted to implement cover cropping as a management strategy for weed suppression in vegetable production. However, few of those experiments were focused on determining the direct effect of cover crop management on both cash crop yields and insect pest and beneficial populations. Indeed, the incorporation of cover cropping systems to improve vegetable crop yields is cha llenging and research in this field is limited. Moreover, most research on cover cropping systems has been focused on winter cover crops, primarily in cotton, corn, wheat etc. and more often in temperate climates than in subtropical and tropical systems. T rials conducted on cover crops in vegetable production systems are primarily focused on cover crop efficacy on weed suppression and associated data on the cover crops ability to supply nutrient and reduce insect pest populations to subsequent crops is limi ted. To our knowledge, there have been no studies that involve the investigation of the subsequent effects of cover crops on insect populations and yield of cash crops cultivated into cover crops residues that are either incorporated or laid on the soil su rface.
34 The objective of this research was to investigate cover crop planting and management strategy that is suitable for optimizing vegetable production in tropical environments The specific objectives pursued were to: 1. Identify the cover crop planting st rategy and tillage method that results in the greatest cabbage yield 2. Determine via monitoring how the cover crop planting strategies and tillage method influence key insect pests and beneficial populations
35 CHAPTER 2 CABBAGE RESPONSE TO PIGEON PEA ( Ca janus cajan (L .) Millsp.) AND SORGHUM SUDANGRASS [ Sorghum bicolor (L.) MOENCH VAR. sudanense (PIPER) HITCHC.] COVER CROP FERTILTY AND RESIDUE MANAGEMENT In tropical and subtropical farming systems where soil erosion poses a significant threat to farm sus tainability, vegetable productivity and profitability can be improved by integration of cover crops in the farming system. For instance, intensive vegetable production systems are usually associated with removal of a considerable amount of nutrients from t he soil that is consequently impacted the soil surface layer that, when those nutrients are not readily replaced, may render it difficult to grow a next crop especially in tropical farming systems where nutrients are expensive. Other consequences of soil s urface layer impairing especially in conventionally tilled vegetable production systems, are microbial activity impediment and reduction of nutrient availability (Burke et al., 1989). Over time, repeated tillage has been shown to reduce soil organic matter (Karlen et al., 1990) and deteriorate soil structure (Reicosky et al., 1997 ) In research conducted on the use of cover crops in vegetable production systems, Creamer et al. (1996) and Cher et al. (2006) reported that the use of cover crops in vegetable p roduction systems is one way to replenish the soil surface layer with active soil organic matter and readily available nutrients. Therefore, inclusion of cover crops in the crop rotation turns out to be important to enhance soil quality and fertility and m aximize crop productivity. However, several factors need to be considered to integrate cover crops in a farming system. The type of cover crop (legume vs non legume), the species and sometimes cultivar, the season (winter vs summer), the site of cultivatio n (temperate vs tropical) and tillage management are among the most important factors to consider when incorporating cover crops in an agricultural
36 production system. This study was focused on the use of summer cover crops to improve vegetable production i n subtropical and tropical agro ecosystems. Summer cover crops have potential for enhancing soil quality, fertility and crop yield in subtropical and tropical pr oduction systems (Wang et al., 2003a; Wang and Waldemar, 2006). Nutrient retention can be enhan ced by the integration of summer cover crops. In tropical areas including Florida, heavy rainfall in summer months remain a major impediment to maintain nutrients within the surface layer area due to erosion and leaching (Wang et al., 2005). P igeon pea an d sorghum sudangrass are suitable summer cover crop species for tropical and subtropical farming systems because they generate significant biomass within a short period of time. For instance, top growth biomass production for pigeon pea has been reported t o be about 40 tons of fresh weight green matter per hectare (35 tons a 1 ) and up to 3 tons ha 1 of dry weight, contributing to about 57 kg N ha 1 per ton of dry weight (Valenzuela et Smith, 2002). In Florida, pigeon pea to growth has been found to be conta ined between 3.5 and 6.5 tons ha 1 Plant heights can reach up to 150 cm at 14 weeks at summer planting (Valenzuela and Smith, 2002). Sorghum sudangrass is very effective in adding soil organic matter, reducing nutrient leaching, and suppressing weeds. Vale nzuela and Smith (2002) followed by Clark (2007) reported that Sorghum sudangrass hybrids remain the number one cover crop species in terms of production of organic matter per acre and at a lower seed cost than any major cover crop grown in the United Stat es. Integration of sorghum sudangrass in a rotation can recycle up to 172 kg N ha 1 and 13.9 ton ha 1 of dry weight (Baldwin and Creamer, 2006 ). Jacobs (1995) found that on a low producing muck soil in New York where yields of onion were less
37 than one third of the local average, integration of sorghum sudangrass in only one year rejuvenated the soil to an almost similar condition to newly cleared land. Research conducted with sorghum sudangrass as a cover crop on potato in Colorado showed that sorghum sudang rass contributed to enhancing potato tuber quality and total m arketable yield (Delgado, et al., 2007). According to Delgado and Lemunyon (2006), sorghum sudangrass contributed to the increase in nutrient absorption efficiency on a high pH sandy soil. Pi geo n pea is a promising summer cover crop based on its cultural traits. Food and Agriculture Organization (FAO), 2008, reported that worldwide, pigeon pea farming increased at an annual rate from approximately 2.7 million hectares in 1961 to about 4.6 million hectares in 2007. Pigeon pea in the US is mostly cu ltivated in Hawaii. However, Li et al. ( 2012) reported that pigeon pea had potential for success in southern Florida agro ecosystems. Pigeon pea is also renowned as having the greater N fixation rate in c omparison to other legume species. In Florida, Reddy et al. (1986a) estimated N fixation by pigeon pea at approximately 250 kg N ha 1 atmospheric N as legume, Barber and Navarro, 1994 reported that pigeon pea released up to 40 kg N ha 1 and 80 kg ha 1 of Phosphorus (P) from root decomposition. The roots of pigeon pea exude organic acids such as citric, piscidic, and tartaric, that help to mobilize P in the ground by making it readily available for plant uptake (Sinclair, 2004 ) In addition, Raghothama (1999) added that the intercropping of pigeon pea with a grass species increased P uptake by the companion grass crop. In the tropics, pigeon peas are cultivated in intercropping systems along with crops such as corn, sorghum and millet. Pigeon pea is a multi purpose crop, and is also used as a food crop for both
38 people and livestock. Several groups of researchers have observed that inclusion of pigeon pea resulted in greater resource use efficiency, more stable or resilient s ystems in the long term and less economic risk to small farmers in the tropics (Waddington et al., 2007; Yadav et al., 1998). Long term yield failure, low soil structure and fertility problems were reversed by including pigeon pea in the rotation sequence system (Singh et al., 2005). In the United States (US), particularly in Hawaii, pigeon pea was first intercropped with pineapple to restore soil organic matter (Valenzuela and Smith, 2002), and performed well in a comparison of summer cover crop species in North Carolina (Creamer and Baldwin, 2000). D espite these outstanding and exceptional performance and cultural traits of both pigeon pea and sorghum sudangrass as cover crops above described, documentation of their utilization in vegetable production syst ems either as single planting or in mixture is very limited. Research on the integration of these two promising summer cover crops on vegetable crop yields could be an asset for the promotion of sustainable and cost effective vegetable production systems t hroughout the south. Therefore, the objective of this study was to assess different planting combinations of sorghum sudangrass and pigeon pea under two tillage strategies with and without additional fertilizer on cabbage yield and quality. It was hypothes ized that a cover crop ping system that included a biculture of sorghum sudangrass and pigeon pea could result in the greatest yield of cabbage in comparison to monocultures of sorghum sudangrass or pigeon pea. Materials and Methods Experimental S ite The ex periment was conducted in Live Oak, Florida at the U niversity of F lorida IFAS North Florida Research and Education Center Suwannee Valley during the
39 summer and fall 2011 and was repeated during the same period in 2012. The soil type was a find deep sandy l oam (websoilsurvey.nrcs.usda.gov), Blanton Foxwort Alpin complex soil series. The average monthly temperature and rainfall of the experimental location during the growing season for 2011and 2012 are presented in Figure 2.1 Experimental Design Treatments were arranged in a split split plot design and were replicated four times. The experiment contained 4 main plots, 16 subplots, and 64 sub subplots. The main plot treatments were randomized within each block and consisted of three cover crop plantings: 1) pigeon pea Cajanus cajan L. Millsp. monoculture (PP); 2) sorghum Sudangrass ( Sorghum bicolor L. Moench.) (SS) monoculture; and 3) a biculture of pigeon pea ( Cajanus cajan L. Millsp.) and sorghum Sudangrass, ( Sorghum bicolor L. Moench.) (SP). These cover cr op plantings were compared to a fourth treatment of no cover crop (NC) as a control (Table 2.1). Subplots were constituted four weeks after cover crops emergence by dividing the main plot factor in half with an application of fertilizer (10 10 10) One hal f of the plot received 57 kg N ha 1 (FERT) and the other half received no fertilizer (NO FERT). The fertilizer analysis was 10% nitrogen (N), 10% phosphorus (P 2 O 5 ) and 10% potassium (K 2 O), and was applied at a rate of 57 kg N ha 1 16 kg P ha 1 and 47.2 kg K ha 1 At cover crop termination, sub subplots were established by splitting subplots with one of two cover crop termination strategies. Cover crops were either mowed with a rotary mower and soil incorporated in a single pass with a rototiller (CT) or c rimped and rolled with a roller crimper (NT constituting thus tilled or no till plots. Main plots measured 12.2 by 70 m (subplots measured 1.5 by 15 meters and sub subplot measured 1.5 by 7.5 m (Figure 2.2). Cabbage was utilized
40 as a test crop to determine effect of fertilized cover crop planting arrangement and tillage management on cabbage quality and yield. Cover Crop Management Prior to planting the cover crops, the experimental site was in native vegeta tion composed predominantly of b ahia grass ( Paspal um notatum ). Plots were disked with a rolling disk harrow. In 2011, cover crops were seeded on August 8 with a Great Plains No Till Grain Drill (model 606 NT, Wichita, KS) 7. 5 in row spacing at a rate of 22.8 kg h a 1 for SS and 57 kg h a 1 for PP The SP wa s seeded using half of the seeding rate for each of the single species: SS 11.4 kg h a 1 and PP 28.5 kg h a 1 In 2012, the seeding rate for SS was doubled in response to insufficient biomass production in 2011 and consequently the SP seeding rate became SS 22.8 kg h a 1 and PP 28.5 kg h a 1 With the same implement used in 2011, cover crops were seeded on July 18 2012. In 2012, fertilizer treatment was assigned four weeks after cover crops emergence in the same manner as 2011. Two weeks before cabbage transpla nting on November 14 cover crops were terminated in the same manner as 2011 (Table 2.2). Cabbage Management Cabbage transplants were produced in the greenhouses on the farm in 72 cell plastic trays and Fafard Superfine Germination mix that consisted of pe at, vermiculite, dolomitic limestone, wetting agent, and a starter charge (Conrad Fafard Inc. Agawam, MA) Seeds were planted on October 24 2011 and September 10 2012. Cabbage transplants were managed for insects and diseases dur ing both years, twice each y ear with Dipel ES ( Libertyville, IL ) at the rate of 28 grams per gallon. Cabbage transplants received 120 ppm N within one week of transplanting. Cabbage (cv. Bravo F1, Harris Seeds, Rochester, NY) was transplanted by hand on November 30, 2011 and October
41 24, 2012 at a density of about 35,000 plants per hectare Sub subplots consisted of two rows of cabbage 7.5 m in length with plant and in sub subplot contained 40 plants. Cabbage was harvested on April 2, 2012 and Februar y 27, 2013. Fertilizer (Super Rainbow Plant Food, Agrium Denver, CO) was applied at tra nsplanting at the rate of 85 kg N ha 1 Liquid ammonium fertilizer was applied to the soil as a drench 4 and 8 weeks after transplanting (WAT) at a rate of 85 kg/ha ( 11% N, 35% P 2 O 5 0% K 2 O, Simplot, Hempstead, TX). Overhead irrigation was used to irrigate when necessary based on soil moisture Insecticides were applied three times during the two year experiment. Aphid infestations threatened the crop each year in the early part of the season. Fulfill 50 WG (Syngenta Canada Inc., Guelph, ON) was applied once in week 8 during the 2011 growing season, and twice (week 6 and week 7) during the 2012 season. In order to control black spot disease cause by a fungus ( Alternari a sp p .) that occurred in both growing season s 10 WAT, fungicides [Bravo (1.7 kg h a 1 ), Endura (9oz h a 1 ), Cabrio (14 oz h a 1 ), Quaris (15 oz h a 1 ), and Maned (2.3 kg ha 1 )] were alternately applied on a weekly basis from 10 WAT to one week before harvest. Weed removal was performed weekly by hand during 2011 and by plowing 8 WAT in 2012 in conventional tillage plots. Data Collection Cover c rop biomass At cover crop termination and before mowing and rolling operation s cover crop and weed biomass were samp led in all sub subplots. A 1 m 2 quadrat was randomly placed perpendicular to the bed in sub subplots and cover crops and weeds were cut at the soil level using hand clippers. Cut plant material was separated by cover crop
42 species, broadleaf weeds and grass weeds. Biomass was dried in a forced air drier at 70 o C for at least 48h until constant weight, and then weighed. Soil nutrients S oil samples were taken at harvest in fall 2011and three times during fall 2012 growing season s: at cover crop termination, 6 WAT and at harvest. During fall 2011, soil samples were sorted into two categories from 32 points of fertilized and unfertilized sub subplots. In order to increase precision, during the 2012 growing season, 10 samples were taken each time and grouped into four categories: 1) four samples from unfertilized sub subplots from four replicates; 2) four from fertilized sub subplots from 4 replicates; 3) one sample from 32 points of unfertilized sub subplots; 4) one sample from 32 points of fertilized sub subplots Samples were collected using a hand probe that was 5 cm in diameter to a soil depth of 15 cm. Six cores were collected in each sub subplot, combined in a bucket and thoroughly mixed prior to submission for analysis. Samples were submitted to Waters Agri cultural Laboratories, Inc. (Camilla, GA) for analysis. Soil samples were analyzed using Mehlic h 1 method for soil nutrient content including nitrate nitrogen (Table 2 3). Weed b iomass in t ransplanted c abbage Weeds removals were performed by hand during f all 2011 growing season and by plowing during fall 2012 one, both at week 8 AT. Prior to the weeding operation, weed biomass was sampled using a 0.5 m 2 quadrat randomly placed along the width within all sub subplots. At harvest a second set of weed samples was collected within every sub subplot. Weed biomass was dried and weighed according to the procedure previously described for cover crop biomass.
43 Cabbage y ield and y ield p arameters The harvest operation was performed on April 2, 2012 for the first growin g season and on February 21, 2013 for the second one. 15 plants were harvested in the middle of each sub subplot. Plants were pulled up, then cut to remove wrapper leaves and weighed to determine fresh weight. Head height, head diameter, and head core widt h were measured and recorded as well. Cabbage yield were determined on a head weight basis. Cabbage head weight ranging within 0.5 kg (1 pound) or mor e was considered as marketable according to the US Standards for Grades of Cabbage (Shelton et al., 1982 ). Statistical Analysis Data from cover crop biomass, weed biomass, cabbage yield and yield parameters were analyzed using repeated measures analysis (PROC GLIMMIX, SAS 9.3, version 2006 2010 by SAS Institute Inc., Cary, NC, USA) in order to determine ma in effects of cover crops planting, fertilizer, and tillage management as well as their possible interactions. Means separation was performed using least squares means (LSMeans). Results were considered significant at P Due to significant interaction s between years and main effect factors, the results are presented by year. Results and Discussion Weather conditions Weather conditions were different between years. Cabbage harvest was delayed in both years due to cold temperatures. During fall 2011, min imum and maximum temperatures (T) were 1 and 26.9 o C; respectively, at the beginning of cabbage growing season, and 6.2 and 33.8 o C at the end of the season. In contrast, during the fall 2012 season, minimum and maximum T were 4.4 and 32.9 o C at the begin ning of
44 the season and 6 and 17 o C at the end, respectively (Figure 2.1). This weather condition may be contributed to decreasing cabbage yields during both years. However, the fact that the weather was cooler in 2012 than 2011, this yield decrease observ ed in cabbage was more important in fall 2012 than fall 2011 as well (Tables 2.11, 2.12, 2.14, 2.15, and 2.16). Soil N itrogen (nitrate) At the end of the fall 2011 season, soil nitrate (NO 3 ) content in fertilized subplots was less than unfertilized plots Inversely, in fall 2012, soil nitrate was greater in fertilized subplots than unfertilized plots (Table 2.3).This may be attributed to improved mineralization and N uptake in fall 2011 than fall 2012. Effect of Fertilizer on Cover Crop and Weed Biomass Cover c rop biomass In 2011, cover crop biomass recorded as dry weight was greater for both SS and SP than PP within both fertilized and unfertilized subplots (Table 2 5). Sorghum sudangrass dry weight was 32% greater within fertilized subplots than unferti lized subplots. Mixture dry weight was similar with SS dry weight within fertilized subplots and was slightly greater within unfertilized subplots. P igeon pea dry weight was not different within both fertilized and unfertilized subplots. In 2012, except fo r PP where dry weight within fertilized subplots was greater than unfertilized subplots, results were the same as for 2011 among and between cover crop species. However, although SP dry weight (4.1 and 1.2 ton ha 1 ) was slightly greater than SS dry weight (3.7 and 1.1 ton ha 1 ) under both fertilization rates, both SP and SS dry weight increased in 2012 compared to 2011 (Table 2 5). This increase observed in SS and SP dry weight may be explained by the fact that their seeding rates were increased in 2012. P i geon pea dry weight
45 increased in 2012 as well. In this case, as PP was seeded at the same seeding rate than 2012, this increase in biomass over that period seemed to be linked with planting date and increase in air temperature during 2012 season (Figure 2. 1). In 2011, during the cover crop growing period the lowest monthly air temperature was below 2 o C. At such a low temperature, PP could not achieve its optimum growth. The optimal growing temperature for PP ranges between 18 30 o C (Valenzuela and Smith, 2002). Based on that, it can be inferred that the lower the minimum monthly air temperature during the growing season, the lower the biomass production for PP. However, because both SS and PP are not cold tolerant, the greater biomass production of SS comp ared to PP biomass may be attributed to a greater potential for SS to scavenge nutrients due to its expansive root system and produce greater biomass. This observation is also corroborated by Clark A. (2007) reporting that SS has potential to produce more organic matter per acre, and at a less expense than any major cover crop cultivated in the US. The greater biomass production observed within SS fertilized subplots than SS unfertilized subplots is in accordance with Clark (2007) who reported that SS usual ly required supplemental N for optimum growth. Though not significant, the mean dry weight observed in SP subplots was numerically greater compared to the other subplots is in accordance with previous studies, in particular those of Treadwell D. et al., 20 08; Balkcom et al., 2005, who concluded that cover crop combinations have the potential to increase biomass production compared to monoculture cover crop plantings. Weed biomass at cover crop termination Grass species, particularly large crabgrass ( Digitar ia sanguinalis ), crowfootgrass ( Dactyloctenium aegyptium ) and nutsedge ( Cyperaceae spp. ) were predominant during cover crop growth period over both years. Cover crop species and fertilizer interaction
46 effects were significant over both seasons for grass an d total weed dry weight at CC termination ( P value= 0.0005 and 0.0001 for one and two; respectively). In both growing seasons, total weeds dry weights were reduced within SS and SP subplots compared to PP subplots at CC termination independently of the pre sence of N added in week four after CC emergence ( T ables 3 6 and 3 7). Sorghum sudangrass and SP weed suppression potential seemed to be independent of the addition of fertilizer. Grass weed dry weights among unfertilized subplots were similar in 2011 and 2012. Additionally, total weeds dry weights were similar among fertilized SS and SP subplots and unfertilized SS and SP subplots; respectively (Table 2 6 and 2 7). During both years, there was biomass in PP fertilized plots (1, 750 kg ha 1 and 630 kg ha 1 respectively, 2011 and 2012) co mpared to PP unfertilized plots (630 kg ha 1 and 250 kg ha 1 respectively, 2011 and 2012) The addition of fertilizer to the legume cover crop benefited weed growth more than the addition of fertilizer to SS. Wee d biomass during cabbage production Following cabbage transplanting, there was a predominance of broadleaf species compared to grass species. Florida pusley ( Richardia scabra L.) was more abundant among broadleaf species observed in transplanted cabbage du ring both growing seasons. Because weeds removal was not performed in all subplots after cabbage transplanting, results on weed dry weight are represent data collected 8 WAT than weed dry weight obtained at harvest. In fall 2011, except within SS subplots where weed dry weight was lower than the control of no cover crop, there were no significant main effects of cover crops or fertilizer on weed dry weight compared to the control 8 WAT (Table 2 8). However, cover crop termination method did affect weed biom ass in transplanted cabbage. Weed dry weight was reduced in subplots where cover crops
47 were incorporated compared to subplots that were crimped and rolled (Table 2 8). The greatest weed dry weight was recorded within NT sub subplots. The increase in weed b iomass may be the result of a continued progression of weed growth in these sub subplots after cover crop termination. The lower weed biomass recorded in CT sub subplots may be due to the fact that weed seeds were buried by tillage and, moreover the crit ical weed free period for cabbage is between 3 WAT and 4 WAT (Ontario CropIPM, 2009) and that weeds emerging after that critical weed free period were smothered by well established cabbage canopies in those sub subplots. In fall 2011, broad leaf dry weigh t or total weeds dry weight were not influenced by main effects of cover crops or fertilizer at 8 WAT. However, cover crop termination method and fertilizer did influence grass (monocots) weed dry weight. Weed (monocots) dry weight was lower within unfer tilized CT sub subplots than fertilized CT sub subplot weight was lower within CT sub subplots than NT sub subplots (Table 2 9). This is consistent with observations made in fall 2011. It may be inferred that the ability of the cover crops to suppress weeds were not fertilizer dependent when cover crop biomass was incorporated. However, among NT systems, the addition of N fertilizer to cover crops during the early growth stage resulted in the production of more biomass, more surface residue, and thus more weed suppressive ability compared to systems that included tillage and incorporation of cover residue. Cabbage Yield and Yield Parameters Cover crop planting and fertilizer main effects did not influence cabbage yield or yield parameters in 2011 (Table 2 4) In 2011, there were two significant two way interactions (cover crop x cover crop termination method, and fertilizer x cover crop
48 termination methods) for cabbage yield a nd yield parameters. In 2012 the main effect of cover crop did not affect marketable yield, percent of head weight, and wrapper leaves However, in 2012, there was a significant three way interaction (cover crop x fertilizer x cover crop termination metho ds) for every parameter studied ( T able 2 4) In fall 2 011, total yields ranged from 30 to 54 ton ha 1 averaged across all treatments, in fall 20 12, total yields ranged from 15 to 47 ton ha 1 Market able head weight ranged from 6 to 38 ton ha 1 in fall 201 1 and from 3 to 17 ton ha 1 in fall 2012. The percent of head weights relative to head weight divided by total plant weight ( sum of head and wrapper leaves weights ) ranged from 41.7% to 65.7% in fall 2011 and from 6.7% to 48.5% in fal l 2012.Total yield, pe rcent of heads, and marketable heads were greater in fall 2011 than in fall 2012 (Tables 2 4, 2 10, 2 11 and 2 16; respectively). This difference in both years may generally be due to the fact that it was cooler in fall 2012 than fall 2011 (Figure 2 1). Th e main effect of Pigeon pea in sub subplots was associated with in an increase in yield consistently both years. This is resulted to the greater amount of readily available soil NO 3 released within these sub subplots. Yields were lowest in SP NT plots in f all 2011 and in SS NT plots in fall 2012. Interaction Effects on C abbage Y ield and Y ield P arameters Fall 2011 Cover crop (CC) x Land preparation [ cover crop termination methods (CTM) ] and fertilizer x CTM interactions effect s significantly impacted total yield (TY), percent of head weight ( PHW), and marketable heads (MH ). Cover crop x fertilizer did not a ffect yield or yield parameters (Table 2 4). Therefore, it can be inferred that CTM had more influence on yield than CC and fertilizer. Yields were signi ficantly greater in all CT sub subplots than NT sub subplots. Cover crops did not influence yields in CT sub subplots (Tables 2 10, 2 11, 2 12 and 2 13). The higher yield production observed in CT
49 sub subplots may be attributed to a better mineralization r ate of incorporated residues and therefore resulted in more readily available soil NO 3 for cabbage uptake. However, TY and PHW within SS CT sub subplots were not significantly different than TY and PHW within PP NT sub subplots. This may be explained by a possible immobilization of soil nitrogen within SS NT sub subplots by soil microbes representing main engine of the soil mineralization. As a result, less soil NO 3 was available in these sub subplots for plant uptake compared to PP sub subplots. Balkcom et al. (2007 2011 ) pointed out that the presence of high carbon to nitrogen ration referring to nitrogen immobilization by grass cover crop spec ies incorporated into the soil, m ay be due to nitrogen to carbon ratio as reported by Balkcom et al. (2007 2011 ). Within NT treatments, yields from sub till system, the legume cover crop contributed to an increase of cabbage yield compared to the grass cover crop. Cabbage total yiel d, percent of head weight, and marketable yield were all influenced by the interaction effects of fertilizer x CTM (Table 2 4). However, yields were significantly higher within all CT sub subplots than NT sub subplots which means incorporated residues was a more important influence on yields than fert ilized residues on the surface ( Tables 2 14 and 2 15). Within fertilized CT sub subplots, yields were greater than unfertilized CT sub subplots. In contrast, although not significant, yields from unfertilized N T sub subplots trended greater than fertilized NT sub subplots. Fertilized cover crops managed as NT with residues remaining on the soil surface had minimal influence on total cabbage yield compared to unfertilized cover crop NT sub subplots. The lack of y ield response attributed to cover crop fertilizer treatments among
50 NT systems may be explained by cooler soil temperatures under the dense fertilized CC residue that possibly reduced cabbage growth and, as a result, decreased yields. Yield Parameters Y ield parameters wrapper leaf, head height, and head core width generally reflected yield results. Cover crop x CTM interaction effects were significantly influenced yield parameters (Table 2 4). Also, CTM main effect was significant. That means CTM main effect counts for more variability than cover crops. In other words, CTM was a more important influence on yield parameters. Head diameter (HD) was similar among CT sub subplots and NT sub subplots. Among the NT sub subplots, HD was greater from plots planted to PP and SS monocultures than the SP mixture. Head height (HH) was similar among CT sub subplots. Head height was significantly higher within NT PP, SS, and NC sub subplots than NT SP sub subplots. Head core width (HCW) was not significantly different wi thin CT sub subplots and PP and SS NT sub subplots. HCW within CT sub subplots was greater than HCW within NT PP and SS sub subplots (Tables 2 12, 2 13, 2 14, and 2 15). Based on these results, it can be inferred that HD and HH parameters were better indic ators of yield in cabbage than HCW. Fall 2012 Significant three way interaction effects (CC x CTM x fertilizer) were recorded for every measured parameter in fall 2012 (Table 2 4). Thus, results are presented only for the three way interaction effects exce pt for marketable heads. In that instance, the 3 way interaction ( P value= 0.0343) was deemed weak because CC, CTM and fertilizer factor influences on head weight were predominantly influenced by the two way interaction of CC x CTM. Consequently, the two w ay interaction (CC x CTM) effect (P<0.0001) was presented instead for MH.
51 Cover crop x c over crop termination methods interaction effect on MH M arketable head was significantly greater within CT sub subplots than NT sub subplots. This may be explained by t he fact that it was cool during fall 2012 growing season, and that soil temperature was lower under residues cover crops even within sub subplots where residues were incorporated into the soil. This result is in accordance with Walters and Young (2008) fin dings on zucchini with winter rye mulch in cool weather M arketable head yield was improved in PP and NC sun sub plots regardless of tillage compared to SS and SP sub subplots. This may be attributed to the fact that soil NO 3 was more accessible within the se plots. C over crop x f ertilizer x CTM interaction effects on TY, PHW, and WW Total yield was better within PP and NC plots when all the three main effects were present. TY was in general tend to be better within plots were cover crop residues were incorp orated than plots where cover crop residues were rolled on the soil surface. T otal yield was also great er when fertilized CC residues were absent within sub subplots with PP and NC both within CT and NT sub subplots (Table 3 15). TY was similar within CT sub subplots with fertilized PP residues, no till sub subplots with fertilized PP residues, and CT sub subplots with fertilized NC residues. T otal yield was similar within CT fertilized sub subplots with NT fertilized with PP residues. Inversely, TY was s ignificantly greater within NT fertilized SS sub subplots than CT fertilized sub subplots. This may be due to N confiscation via dense incorporated SS residue biomass. Although, within PP and SP subplots, tillage did not significantly influence TY when fer tilizer was present, the inverse was observed with PHW where PHW were significantly higher within CT fertilized PP and SP sub subplots, respectively ( T able 3 15). That means tillage played anyway an important role in
52 cabbage head formation. CC x fertilize r x CTM had a similar influence on wrapper leaves weight. However, a significant difference between WW issued from fertilized CT SP sub subplots and NT fertilized sub subplot was recorded. The lowest yields were observed with SS residues when tillage and f ertilizer were absent. C over crop x f ertilizer x CTM interaction effects on yield parameters C over crops x Fertilizer x CTM interaction effects for yield parameters were similar with 3 way interaction effects for yields. However, unlike yield, there were n o significant differences on HD when all the three factors were present than when either tillage or fertilizer was absent within sub subplots with PP (Table 2 16). P igeon pea and NC were significantly influence HD, HH, and HCW, respectively either when all the three factors were present or when tillage was absent. There was a general trend, independently of the CC main effect, for results to be significantly influenced by tillage (incorporated cover crop residues) than no till (cover crop residues laid on t he soil surface) either in presence or absence of fertilized residues. Overall, yield parameters as well as yields were lowest within SS residues sub subplots when tillage and fertilizer were absent. Conclusions There were several environmental differences between both growing seasons. For instance, c over crop biomass residues were denser in fall 2012 than fall 2011; fall 2012 growing season was cooler than fall 2011 ; and an extra 34 kg of N per hectare were added to transplanted cabbage in fall 2012 growin g season that provided additional nutrients to bolster cabbage recovery following unseasonably cold temperatures.
53 Overall, c abbage total and marketable yields were greater (44% to 50% for TY and 50% to 86% for MH) in fall 2011 than fall 2012. In fall 2011, PP, SP, and NC coupled with CT produced greater cabbage yield s In fall 2012, PP and NC produced greater yield s in presence of CT and fertilizer. Cabbage yield was greater within NT PP sub subplots than SS, SP, and NC sub subplots Within NT PP sub subplo ts, cabbage yield was greater when fertilizer was present. It can be concluded that the addition of 57 kg N ha 1 beforehand during cover crop growth benefited cabbage yield even with PP legume cover crop It can be concluded as well that incorporation of C C by tillage promoted mineralization and therefore, resulted in greater cabbage yield than when residues cover crops were laid on the soil surface as mulch. Overall, for a better result, i t would be enviable for vegetable grower s working on cover crop ping systems to incorporate cover crop residue s into the soil instead of laying them on the soil surface. It would be beneficial as well whether a portion of fertilizer would apply beforehand to cover crops during cover crop growth. Finally, when the cultural o bjective within especially NT systems is yield increased, the use of PP could be the better option.
54 A B Figure 2 1. Monthly air temperature at a height of 60 cm, relative humidity, and rainfall at a height of 2m ; A) Data related to 2 011 growing season; B ) Data related 2012 growing season; both downloaded from Florida Automated Weather Network (FAWN) for Live Oak, Florida.
55 Table 2 1. Cover crops repartition in kg ha 1 and seeding rate establishment for summer 2011 and 2012 growing sea sons in Live Oak Florida Growing season Pigeon pea (PP) Sorghum sudangrass (SS) Mixture (PP xSS) PP SS 2011 50 20 25 10 2012 50 40 25 20
56 Table 2 2. Main effect treatments arrangement according to the experimental design established during growing season 2011 and 2012 in Live Oak Florida. z Even numbers correspond to no till and odd numbers to tillage. NC: no cove r (control); PP: pigeon pea (legume); SS: sorghum sudangrass (grass); SP: mixture b/w PP and SS. Treatment Z Cover Crop y Fertilization x Tillage Methods w 1 NC Y CT NC N CT 2 NC Y NT NC N NT 3 PP Y CT PP N CT 4 PP Y NT PP N NT 5 SS Y CT SS N CT 6 SS Y NT SS N NT 7 SP Y CT SP N CT 8 SP Y NT SP N NT
57 Figure 2 2. Sketch of the split split plot design of the experiment laid out in Live Oak, Florida
58 Table 2 3. Soil chemica l properties (0 15 cm depth) of the experimental site in Live Oak Florida during fall 2011 and 2012. Fall 2011 P K Mg Ca pH S B Zn Mn Fe Cu Nitrate N Fert. Soil composite At harvest 204 105 69 720 6.1 68 0.8 5.1 8 40 2.3 11.16 Unfert. Soil composite At harvest 165 91M 73 699 6.1 58 0.6 3.5 7 33 2.1 20.32 Fall 2012 Fert. Soil composite At cover crop termination 120 44 40 593 5.5 43 0.2 2.8 8 31 1.6 7.23 Week 6 after transplanting 120 110 38 572 5.8 15 0.3 2.6 7 24 1.1 16.97 At harvest 117 132 42 682 5.4 22 0.7 3.5 11 30 1.5 52.95 Unfert. Soil composite At cover crop termination 106 34 43 586 6.1 6 0.2 2.4 7 25 1.5 3.39 Week 6 after transplanting 103 73 35 526 6.0 6 0.3 1.9 6 27 1 19.47 At harvest 11 0 124 40 560 5.5 28 0.6 2.6 9 30V 1.3 28.04
59 Table 2 4. Analysis of varian ce summary for cover for cover crop dry weight, weed dry weight, cabbage total head weight, marketable head, percentage of head weight, wrapper leaf, head diameter, head height, and head core width as affected by cover crop planting type, fertilizer, and c over crop termination methods. z Cover crop; y single Piegon pea and single sorghum sudangrass planting, biculture of pigeon pea and sorghum sudangrass, and fallow no c over x treatment consisting of addition of 57kg/ha to half of each cover crops planting plot; w At cover crop termination, one part of each cover crop planting was mowed and incorporated into the soil and the other part was crimped and rolled on the soil sur face. ACT: at cover crop termination; WAT: week after transplanting; G: grass; BL: broad leaf; Tot.: total; THW: total head w eight MH: marketable head ( 0.5 kg) ; PHW: percentage of head weight; WW: wrapper leaf; HD: head diameter; HH: head height; HCW: head core width Season Source df CDW z Weeds dry weight Yield and yield parameters ACT 8 WAT THW MH PHW WW HD HH HCW G BL Tot. G BL Tot. Fall 2011 Replication 3 Planting y 3 *** *** ns *** ns ns ns ns ns ns ns ns ns ns Fertilization x 1 *** *** ns *** ns ns ns ns ns ns ns ns ns Land P w 1 n/a n/a n/a n/a ns *** *** *** *** *** *** *** 2 way interactions PlantingxLand P 3 n/a n/a n /a n/a ns ns ns *** ** *** ** ** PlantingxFertilization 3 *** ** ns ns ns ns ns ns ns ns ns ns ns Land PxFertilization 1 n/a n/a n/a n/a ns ns ns ** *** *** *** *** ** 3 way interactions PlantingxLand Pxfert. 3 n/a n/a n/a n/ a ns ns ns ns ns ns ns ns ns ns Fall 2012 Replication 3 Planting 3 ** ** ** ** ns ns ns ** ns ns ns ** ** ** Fertilization 1 *** ns ns ns ns ns *** *** *** *** *** *** *** Land P 1 n/a n/a n/a n/a ns ns ns *** *** *** *** *** *** *** 2 way interactions PlantingxLand P 3 n/a n/a n/a n/a ns ns ns *** *** *** ns ** ** PlantingxFertilization 3 *** ns ns ns ns ns ns ns ns ns ns Land PxFertilization 1 n/a n/a n/a n/a ns ns ns ns ** 3 way interaction s PlantingxLand Pxfert. 3 n/a n/a n/a n/a ns ns ns ** ** ** ** ** **
60 A B C Figure 2 3. View of the experiment before and at cover crop (CC) termination. A) CC field one week before termination; B) CC field after mowing and rolling crimping; C) exp erimental site during incorporation of CC residues by tillage.
61 Table 2 5. Interaction effects of cover crop species and fertilizer on cover crop dry weight in g m 2 dried at 70 o C for 48 hours. Data sampled at cover crop termination in summer 2011 and 2 012 in Live Oak Florida. Summer 2011 Summer 2012 Fertilization z PP SS SP PP SS SP 57 0.2 Bc 2.5 Aa 2.5 Aa 1.9 Bb 3.7 Aa 4.1 Aa 0 0.2 Bc 0.8 ABbc 1.1 Ab 1.1 Ac 1.1 Ac 1.2 Ac PP= pigeon pea; SS= sorghum sudangrass; SP= mixture between pigeon pea and sorghum sudangrass z fertilization in kg/ha added week 4 after cover crops emergence. Mean within rows having same uppercase letters and means within columns having same lowercase l etter s
62 Table 2 6. Interaction effects of cover crop species and fertilizer on weed dry weight in g m 2 dried at 70 o C for 48 hours. Data sampled at cover crop terminat ion in summer 2011 in Live Oak Florida. Grass Total Fertilization z PP SS SP NC PP SS SP NC 57 165 Bb 15 Cc 42 Cc 249 Aa 175 Bb 16 Cd 43 Ccd 264 Aa 0 55 Ac 9 Ac 8 Ac 73 Ac 63 ABcd 9 Bd 9 Bd 90 Ac S.E. 23 23 23 23 24 24 24 24 PP: pigeon pea; SS: sorghum sudangrass; SP: mixture between pigeon pea and sorghum sudangrass NC: no cover crop (control); z fertilization in kg/ha added wee k 4 after cover crops emergence; S.E.: standard error Mean within rows having same uppercase letters and means within columns having same lowercase l etter s ces
63 Table 2 7. Interaction effects of cover crop species and fertilizer on weed dry weight in g.m 2 dried at 70 o C for 48 hours. Data sampled at cover crop termination in summer 201 2 in Live Oak Florida Grass Total Fertilization z PP SS SP NC PP SS SP NC 57 48 Bb 4 Cc 9 Cc 123 Aa 63 Bb 7 Cd 14 Ccd 145 Aa 0 18 Ac 11 Ac 12 Ac 48 Ac 25 ABcd 17 Bd 16 Bd 89 Ac S.E 16 16 16 16 14 14 14 14 PP: pigeon pea; SS: sorghum sudangrass; SP: mixture between pigeon pea and sorghum sudangrass NC: no cover crop; z fertilization in kg/ha added week 4 after cover crops emergence. SE: standard error Mean wi thin rows having same uppercase letters and means within columns having same lowercase l etter s
64 Table 2 8. Effects of cover crops, fertilizer, and tillage on weed dry weight in g m 2 in cabbage (Brassica oleracea cv. Bravo). Data sampled week 8 after transplanting in fall 2011 in Live Oak, Florida. Main effects Grass Broadleaf Total Cover crops treatment Pigeon pea 0.01 0.84 ab 0.85 ab Sorghum sudan. 0.01 0.44 b 0.45 b Mixture 0.10 1.63 ab 1.8 ab No cover 0.00 2.44 a 2.44 a S.E.M. 0.06 0.59 0.60 P value 0.2612 0. 0932 0.0793 Fertilization treatment Yes z 0.02 0.99 1.02 No 0.06 1.68 1.74 S.E.M. 0.04 0.42 0.41 P value 0.5851 0.2512 0.2237 Tillage treatment Till 0.01 0.62 b 0.63 b No till 0.07 2.1 a 2.13 a S.E.M. 0.04 0.42 0.41 P value 0.3149 0.01 93 0.0139 z 57 kg of N/ha added week 4 after cover crops emergence. Means separation within columns grouped by LSMeans at P
65 Table 2 9. Interaction effects of fertilizer and cover crop termin ation method; cover crop species and cover crop termination method on weed dry weight in transplanted cabbage (Brass ica oleracea cv. Bravo) in g.m 2 dried at 70 oC for 48 hours. Data collected in 2012 in Live Oak Florida. Grass z YES x No Broad leaf y Termination Yes No PP SS SP NC Till w 0.9A a 0.1Bb 3.5 Ac 1.2 Ac 3.2 Ac 4.1 A c 0.0 Bd 7.2 Ac No till v 0.00Ab 0.3 Aab 17.8Bb 49.6 Aa 24.0Bb 30.5Bb 18.6Bb 61.7Aa SE 0.3 0.3 3.3 3.3 4.7 4.7 4.7 4.7 z Data collect ed week 8 after transplanting; y data collected at harvest; w cover crop incorporated into the soil; v cover crop crim ped and rolled on the soil surface ; x 57 kg of N (10 10 10) added to half of the experiment week 4 after cover crop emergence; SE: standard error; PP: pigeon pea; SS: sorghum sudangrass; SP: mixture between pigeon pea and sorghum sudangrass NC: no cover (co ntrol); m ean within rows having same uppercase letters and means within columns having same lowercase l etter s .05 based on LSMeans.
66 Table 2 10. Interaction effects of cover crop species and cover crop termination met hod on cabbage ( Brassica oleracea cv. Bravo) total yield and percent of head weight at harvest in fall 2011 in Live Oak, Florida. Total yield ( ton ha 1 ) Proportion of head weight (%) Ter mination PP SS SP NC PP SS SP NC Till z 53 Aa 47 Aab 54 Aa 54 Aa 67.3 Aa 63.6 Aab 67.5 Aa 65.3 Aa No till y 44 Abc 38 ABcd 30 Bd 41 ABcd 59.2 Abc 55.5 ABcd 41.7 Bd 52 .0 ABcd z Cover crops mowed and incorporated into the soil by tillage; y cover crops crimped and rolled as mulch on the soil surface; PP: pigeon pea; SS: sorghum sudangrass; SP: mixture between pigeon pea and sorghum sudangrass NC:no cover (control); m ean s within rows having same uppercase letters and means within columns having same lowercase l etter s P value interaction (planting*Land) P =0.0055 for total yield and 0.0006 for proportion of head weight.
67 Table 2 11. Interaction effects of cover crop species and cover crop terminati on method on cabbage ( Brassica oleracea cv. Bravo) wrapper leaf and marketable head at harvest in fall 2011 in Live Oak, Florida. Wrapper leaf ( ton ha 1 ) Marketable head ( ton ha 1 ) Termination PP SS SP NC PP SS SP NC Till z 15 Aa 15 Aab 17 Aa 15 Aa 33 Aa 30 Aab 38 Aa 36 Aa No till y 15 Abc 14 ABcd 12 Bd 14 ABcd 24 Abc 8 ABcd 6 Bd 9 ABcd z Cover crop s mowed and incorporated into the soil by tillage; y cover crops crimped and rolled as mulch on the soil surface; PP: pigeon pea; SS: sorghum sudangrass; SP: mixture between pigeon pea and sorghum sudangrass NC:no cover (control); m ean s within rows having s ame uppercase letters and means within columns having same lowercase l etter s P value interaction (planting*Land) P =0.0094 for wrapper leaf and 0.0003 for marketable head.
68 Table 2 12. Interaction effects of cover crop species and cover crop termination method on cabbage ( Brassica oleracea cv. Bravo) head diameter and head height at harvest in fall 2011 in Live Oak, Florida. Head diameter (cm) Head height (cm) Termination PP S S SP NC PP SS SP NC Till z 13.7 Aa 13.4 Aab 14.3 Aa 13.6 Aa 12.4 Aa 12.2 Aa 12.4 Aa 12.4 Aa No till y 11.9 Abc 11.5 Ac 9.7 Bd 10.4 ABcd 10.8 Ab 10.2 Ab 8. 7 Bc 9.5 ABbc z Cover crops mowed and incorporated into the soil by tillage; y cover crops crimped and rolled as mulch on the soil surface; PP: pigeon pea; SS: sorghum sudangrass; SP: mixture between pigeon pea and sorghum sudangrass NC:no cover (cont rol); m ean s within rows having same uppercase letters and means within columns having same lowercase l etter s are not significantly different at P P value interaction (planting*Land) P =0.0002 for head diameter and 0.0037 for head height.
69 Table 2 13. Interaction effects of cover crop species and cover crop termination method on cabbage ( Brassica oleracea cv. Bravo ) head core width at harvest in fall 2011 in Live Oak, Florida. Head core width (cm) Termination PP SS SP NC Till z 3.0 Aa 2.9 Aab 3.0 Aa 2.9 Aab No till y 2.6 Aabc 2.5 Abc 2.1 Bd 2.3 ABcd z Cover crops mowed and incorporated into the soil by tillage; y cover crops crimped and rolled as mulch on the soil surface; PP: pigeon pea; SS: sorghum sudangra ss; SP: mixture between pigeon pea and sorghum sudangrass NC:no cover (control); m ean s within rows having same uppercase letters and means within columns having same lowercase l etter s P value interaction (planting*Land) P =0.0033.
70 Table 2 14 Interaction effects of fertilized cover crop residues and cover crop termination method on cabbage ( Brassica oleracea cv. Bravo) yields and yield parameters at harvest in fall 2011 in Live Oak, Flo rida. TY PHW HD HH HCW Termination 57 z 0 y 57 0 57 0 57 0 57 0 Till x 54 Aa 51 Bb 66.8Aa 65.1Aa 14.3Aa 13.2Bb 12.8Aa 11.9Bb 3.0Aa 2.9Aa No till w 35 Ac 41 Ac 46.3Bc 57.9Ab 10.2Bd 11.5Ac 9.3Bd 10.2Ac 2.3Bc 2.5Ab z 57 kg N ha 1 (10 10 10) added to half of the experiment week 4 after cover crop emergence; y the other half with no fertilizer (0 kg N ha 1 ) ; x Cover crops mowed and incorporated into the soil by tillage; w cover crops crimped and rolled as mulch on the soil surface; TY: total yield in ton ha 1 ; PHW: proportion of head weight in % ; HD: head diameter; HH: head height; and HCW: head core width; respectively in cm. M ean s within rows having same uppercase letters and means within columns having same lowercase l etter s are not significantly differ
71 Tab le 2 15 Interaction effects of fertilized cover crop residues and cover crop termination method on cabbage ( Brassica oleracea cv. Bravo) wrapper leaf weight and marketable yield in ton ha 1 at harvest i n fall 2011 in Live Oak, Florida. WW MH 57 z 0 y 57 0 Till x 17 Aa 15 B b 38 Aa 30 Bb No till w 14 Ac 11 A c 18 Ac 21 Ac z 57 kg of N (10 10 10) added to half of the experiment week 4 after cover crop emergence; y the other half with no fertilizer; x Cover crops mowed and incorporated into the soil by tillage; w cover crops crim ped and rolled as mulch on the soil surface; WW: wrapper leaf; MH: marketable head; m ean s within rows having same uppercase letters and means within columns having same lowercase l etter s s
72 Table 2 16 Interaction effects of cover crop species, fertilizer, and tillage on cabbage ( Brassica oleracea cv. Bravo) total yield and wrapper leaf in ton ha 1 and proportion of head in % at harvest in fall 2012 in Live Oak, Florida. Interaction effects z PP SS SP NC 57 kg of N/ha Total Yield Till y 44 AaA 27 BdB w 30 AcdB 47 AaA No till x 39 AabA 32 AbcAB 26 AdC 30 BcdBC 0 kg of N/ha Till 33 AbcA 24 AdeB 23 AdefB 35 AbA No till 26 BdA 15 BfC 20 AefBC 23 BdefABC 57 kg of N/ha Wrapper leaf Till 23 AaA 20 AbAB 21 abA 21 abA No till 21 AabA 21 AabA 17 cdB 17 cdB 0 kg of N/ha Till 18 AbcA 17 AcdA 17 AcdA 18 AbcA No till 17 BcdA 14 AdA 15 AdA 15 BdA 57 kg of N/ha Prop. of head weight Till 40.9 AaA 22.0 AdeB 24.7 AdB 48.5 AaA No till 38.9 BbcA 24.3 AdB 19.3 BeC 26.8 BcdAB 0 kg of N/ha Till 38.8 A bcB 20.7 AdeC 21.3 AdeC 39.1 AabA No till 28.2 AcdA 6.7 BfC 14.4 AeB 23.9 BdA z Three wa y interaction significant P=0.0 046,0.001 2 & 0. 0031 total yield wrapper leaf & proportion of head respectively. Nitrogen fertilizer (1 0 10 10) was added in half of the experiment at the rate of 57 kg/ha week 4 after cover crop emergence. y Cover crops mowed and incorporated into the soil by tillage; x cover crops crimped and rolled as mulch on the soil surface. PP: pigeon pea; SS: sorghum sudangrass; SP: mixture (PP+SS); NC: control (no cover); w Pair means within columns having same left uppercase letters, means within rows having same right uppercase lette rs, and
73 Table 2 17 Interaction effects of cover crop species, fertilizer, and tillage on cabbage ( Brassica oleracea cv. Bravo) head diameter, head heigh t, and head core width in cm at harvest in fall 2011 and 2012 in Live Oak, Florida. Fall 2011 z PP Fall 2012 y SS SP NC Interaction effects PP SS SP NC HD 57 kg of N/ha Till x 35.3 32.2 33.2 34.1 26.2 AaA v 14.8 AcC 17.2 AbcBC 27.8 AaA No till w 26.5 25.8 20.9 23.9 24.5 AaA 17.8 AbcB 12.7 BdC 17.5 BbcB 0 kg of N/ha Till 29.4 31.3 34.4 30.3 23.2 AaA 14.8 AcB 14.8 AcB 24.9 AaA No till 29.9 29.4 25.1 25.4 18.7 BbA 5.5 BeB 10.0 BeB 16.1 BbA 57 kg of N/ha HH Till 32.0 30.0 29.4 31.3 22.5 AabA 14.2 AdeB 15.6 AcdB 24.5 AaA No till 24.0 23.0 19.2 22.3 22.0 AabA 15.4 AdeBC 11.1 BfC 15.6 BcdB 0 kg of N/ha Till 26.6 29.2 30.3 27.7 19.9 AcA 12.7 AbB 14.2 AdeB 21.0 AbcA No till 26.6 25.7 22.3 22.8 15.4 BdeA 4.7 BgB 8.8 BfgB 13.3 BeA 57 kg of N/ha HCW Till 7.6 7.1 7.1 7.1 6.4 AaA 4.7 AcdB 4.7 AcdB 6.4 AaA No till 5.9 5.7 4.7 5.4 5.9 AaA 4.7 AcdB 3.3 BefC 4.7 BcdB 0 kg of N/ha Till 7.1 7.1 7.3 6.8 5.5 AbcA 4.3 AdeB 4.3 AdeB 5.7 AabcA No till 6.4 6.2 5.5 5.5 4.7 AcdA 1.5 BgC 2.6 BfgC 4.0 BeB z Three way interaction not significant P=0.2775, 0.2589 & 0.5330 for head diameter, head height & head core width, respectivel y. y Three way interaction s ignificant P=0.02 75,0.0082 & 0.0045 for head diameter, head height & head core width, respectively. Nitrogen fertilizer (10 10 10) was added in half of the experiment at the rate of 57 kg/ha week 4 after cover crop emergence. x Cover crops mowed and incorporated into the soil by tillage; w cover crops crimped and ro lled as mulch on the soil surface. PP: pigeon pea; SS: sorghum sudangrass; SP: mixture (PP+SS); NC: control (no cover); HD: head diameter; HH : head height; HCW: head core width; v Pair means within columns having same left uppercase letters, means within r ows having same right uppercase letters, and means within columns having
74 Figure 2 4. Cabbage pictures collected at harvest for fall 2012 in Live Oak, Florida. A) Represented ca bbage issued from sub subplots with cover crop residue biomass incorporated in the soil by tillage (CT); B) Displayed cabbage issued from sub subplots with cover crop residue biomass rolled and laid as mulch on the soil surface (NT). In each single picture cabbage on the left was issued from unfertilized residue biomass sub subplots and cabbage placed on the right from fertilized residue biomass. PP: pigeon pea; SS: sorghum S.; SP: mixture (SSxPP); ans NC: no cover (control).
75 CHAPTER 3 PIGEON PEA ( Cajanus cajan (L .)Millsp.) AND SORGHUM SUDANGRASS [ Sorghum bicolor (L.) MOENCH VAR. sudanense (PIPER) HITCHC.] MANAGEMENT CHANGES THE POPULATION OF PEST AND BENEFICIAL INSECTS IN CABBAGE. Benefits obtained from the use of cover crops include increasing soil biolog ical activity, creating or reconciling environmentally friendly and sound sustainable ecosystems, and contributing to weed, disease and insect suppression ( Snapp et al. 2005) The bottom line in cover crop integration is an overall enhancement of farm ecol ogy. Cover crops remain important to improve crop quality and t o lower production costs. Cover crops have become a pillar on North American farms. In controlled tillage systems with a suitable variety choice and sufficient biomass, cover crops have potenti al to suppress weeds, diseases, nematodes and insect pests. Farmers and researchers who view the farm as an agro ecosystem have made the use of cover resources. Well tho ught sustainable pest management commences with establishment of healthy soils. However, building healthy soil is not limited to increasing soil organic matter. Soil organic matter increases with the incorporation of animal based residues and crop residues into the soil. Integration of cover crops can lower soil erosion, reduce runoff, enhance water infiltration, soil structure, soil organic matter, and increase soil flora and fauna (Reeves; 1994 ). Research in South Georgia reported that crops grown on biol ogically active soils resist pest pressure far better than those cultivated on low fertility soils. In balanced ecosystems, insect pests can be managed by remained in control by their natural enemies (Sustainable Agriculture Network, 2005). N atural enemie s or
76 beneficial insects include predators, parasitoids, and parasites. Beneficial insects can be attracted by a diversity of cover crop species. Brunson (1991 ) reported that 13 known beneficial insects associated with cover crops were identified during t he vegetable production season in South Georgia. Brunson (1991) identified more than 120 species of beneficial s including arthropods, spiders and ants in cotton fields that were managed with cover crop residues on the soil surface and no insecticides were applied. In Mississippi, Georgia and Alabama research on summer vegetables planted in residues of cool season cover crops illustrated that many beneficial insects relocated from adjacent areas to surface residues to attack crop pests ( Bugg, 1992 ) In con junction with these findings, Tumlinson et al. (1993 ) reported that when crop s are attacked by pest s they transmit chemical signals that attract beneficial insects that are active predators. Cover crop management strategies may also be important tool s lea ding to the modif ication of insect populations and enhance ment of crop productivity. Following this rationale, Altieri (1994) and Reeves (1994) reported that conservation tillage and cover crops can contribute to lower production costs via enhanced soil re lationships and long term soil productivity, increased niche for beneficial insects and greater agro ecosystem stability. Conservation tillage along with cover crops promot es year round natural enemy and pest interactions by providing alternate prey or hos ts, reproductive sites and shield against adverse conditions. Sorghum sudangrass hybrid has been in us e in the US as a summer cover crop on many southeastern farms Sorghum suda n grass has been documented to attract beneficial insects and in particular lad y beetles that help control aphids Epieru (1997) found that cotton grown in combination with various crops including sorghum increased
77 the occurrence of common predators such as coccin e llidae, anthocoridae, spiders, ants, earwings, rove beetles, chrysopid s, and syrphids. Sharma et al. (2004 ) found that sorghum harbored more natural enemies of cotton bollworms than other crops and gave evidence of the migration of predators between sorghum and cotton. Pigeon pea, on the other side, has been found efficient in attracting predator s (arthropods) when intercropped ( Odeny, 2007 Valenzuela and Smith, 2002). Despite cover crops appear ance of play ing a leading role in IPM by maximizing natural enemy pest interactions, research in that area is limited Many publishe d accounts are focused on cover crops and natural enemy pest interactions have been conducted in the north with winter species. C urrently, research on cover crops in conservation tillage systems is conducted primarily in row crop systems such as cotton, co rn, wheat etc. and more often in temperate climates than in subtropical and tropical agro eco systems. McCutcheon et al., (1995) Ruberson et al. (1995) and McCutcheon (2000) stated that further research needs to be focused on cover crops with conservati on tillage in cropping systems in the south to increase beneficial insects. I t is true that cover crops in conservation tillage systems promote a simple approach to managing pest s but more information on the effects of cover crops on key pest and benefici al insect populations are needed to facilitate appropriate decision making. The objective of this 2 year field experiment was to determine how pigeon pea and sorghum sudangrass planting arrangement and tilla ge method influences key pests and beneficial ins ects in cabbage ( Brassica oleracea L.) It was hypothesized that pigeon pea and sorghum sudangrass planting arrangements and termination strategies would
78 different iall y influence the density and diversity of insect pest s and beneficial s in fall cabbage. M aterials and Methods Experimental S ite The experiment was conducted in Live Oak, Florida at the U niversity of F lorida IFAS North Florida Research and Education Center Suwannee Valley during the summer and fall 2011 and was repeated during the same period i n 2012. The soil type was a find deep sandy loam (websoilsurvey.nrcs.usda.gov), Blanton Foxwort Alpin complex soil series. The average monthly temperature and rainfall of the experimental location during the growing season for 2011and 2012 are presented in Figure 2.1 Experimental Design Treatments were arranged in a split split plot design and were replicated four times. The experiment contained 4 main plots, 16 subplots, and 64 sub subplots. The main plot treatments were randomized within each block and consisted of three cover crop plantings: 1) pigeon pea Cajanus cajan L. Millsp. monoculture (PP); 2) sorghum Sudangrass ( Sorghum bicolor L. Moench.) (SS) monoculture; and 3) a biculture of pigeon pea ( Cajanus cajan L. Millsp.) and sorghum Sudangrass, ( Sor ghum bicolor L. Moench.) (SP). These cover crop plantings were compared to a fourth treatment of no cover crop (NC) as a control (Table 3.1). Subplots were constituted four weeks after cover crops emergence by dividing the main plot factor in half with an application of fertilizer (10 10 10). One half of the plot received 57 kg N ha 1 (FERT) and the other half received no fertilizer (NO FERT). The fertilizer analysis was 10% nitrogen (N), 10% phosphorus (P 2 O 5 ) and 10% potassium (K 2 O), and was applied at a r ate of 57 kg N ha 1 16 kg P ha 1 and 47.2 kg K ha 1 At cover crop termination, sub subplots were
79 established by splitting subplots with one of two cover crop termination strategies. Cover crops were either mowed with a rotary mower and soil incorporated in a single pass with a rototiller (CT) or crimped and rolled with a roller crimper (NT constituting thus tilled or no till plots. Main plots measured 12.2 by 70 m (subplots measured 1.5 by 15 meters and sub subplot measured 1.5 by 7.5 m (Figure 3.2). Cab bage was utilized as a test crop to determine effect of fertilized cover crop planting arrangement and tillage management on cabbage quality and yield. Cover Crop Management Prior to planting the cover crops, the experimental site was in native vegetation composed predominantly of bahia grass ( Paspalum notatum ). Plots were disked with a rolling disk harrow. In 2011, cover crops were seeded on August 8 with a Great Plains No Till Grain Drill (model 606 NT, Wichita, KS) 7.5 in row spacing at a rate of 22.8 kg h a 1 for SS and 57 kg h a 1 for PP The SP was seeded using half of the seeding rate for each of the single species: SS 11.4 kg h a 1 and PP 28.5 kg h a 1 In 2012, the seeding rate for SS was doubled in response to insufficient biomass production in 2011 an d consequently the SP seeding rate became SS 22.8 kg h a 1 and PP 28.5 kg h a 1 With the same implement used in 2011, cover crops were seeded on July 18 2012. In 2012, fertilizer treatment was assigned four weeks after cover crops emergence in the same mann er as 2011. Two weeks before cabbage transplanting on November 14 cover crops were terminated in the same manner as 2011 (Table 3.2). Cabbage Management Cabbage transplants were produced in the greenhouses on the farm in 72 cell plastic trays and Fafard S uperfine Germination mix that consisted of peat, vermiculite, dolomitic limestone, wetting agent, and a starter charge (Conrad Fafard Inc. Agawam,
80 MA) Seeds were planted on October 24 2011 and September 10 2012. Cabbage transplants were managed for insects and diseases during both years, twice each year with Dipel ES ( Libertyville, IL ) at the rate of 28 grams per gallon. Cabbage transplants received 120 ppm N within one week of transplanting. Cabbage (cv. Bravo F1, Harris Seeds, Rochester, NY) was transpla nted by hand on November 30, 2011 and October 24, 2012 at a density of about 35,000 plants per hectare. Sub subplots consisted of two rows of cabbage 7.5 m in length with plant and in sub subplot contained 40 plants. Cabba ge was harvested on April 2, 2012 and February 27, 2013. Fertilizer (Super Rainbow Plant Food, Agrium Denver, CO) was applied at transplanting at the rate of 85 kg N ha 1 Liquid ammonium fertilizer was applied to the soil as a drench 4 and 8 weeks afte r transplanting (WAT) at a rate of 85 kg/ha (11% N, 35% P 2 O 5 0% K 2 O, Simplot, Hempstead, TX). Overhead irrigation was used to irrigate when necessary based on soil moisture. Insecticides were applied three times during the two year experiment. Aphid infes tations threatened the crop each year in the early part of the season. Fulfill 50 WG (Syngenta Canada Inc., Guelph, ON) was applied once in week 8 during the 2011 growing season, and twice (week 6 and week 7) during the 2012 season. In order to control bl ack spot disease cause by a fungus ( Alternaria sp p .) that occurred in both growing seasons 10 WAT, fungicides [Bravo (1.7 kg ha 1 ), Endura (9oz ha 1 ), Cabrio (14 oz ha 1 ), Quaris (15 oz ha 1 ), and Maned (2.3 kg ha 1 )] were alternately applied on a weekly b asis from 10 WAT to one week before harvest. Weed removal was performed weekly by hand during 2011 and by plowing 8 WAT in 2012 in conventional tillage plots.
81 Data Collection Sampling Sampling methods were similar during both years. Key cabbage insect pests and beneficial insects were sampled using in situ count s unbaited (TRC Inc.) yellow sticky cards, and pitfall traps (Figure 3 .3) In both years, sampling started two week after cabbage transplanting, continuing every two weeks until cabbage head fill. Sampling started on December 19, 2011 and was terminated on March 12, 2012 for the 1 st year. During the 2 nd year, sampling started on November 12, 2012 and finished on January 14, 2013. Systematic sampling was established by collecting samples every other week from a starting point randomly chosen d uring the setting of the first traps (Figure 3 .4). In the visual (in situ) count, a total of five plants were sampled from the two rows of each sub subplot. The youngest cabbage l eaves were carefully obser ved (F igure 3 .3C) for aphids, whiteflies and worms including (Diamondback moth and Cabbage looper). Pitfall and yellow sticky traps were placed in the field for four days and then collected, taken back to the laboratory at horticultural sciences department of University of Florida for counting and identification. In the field, yellow cards were vertically attached on stakes, randomly placed in each sub subplot, at a height greater tha n 0.30 m and less than 1 m (Figure 3 .3A). For pitfall traps, transparent solo cups were put in previously dug holes in each sub subplot (Figure 3 .3B), and filled with water mixed with detergent to disrupt the surface tension (MCNeill et al., 2012; Webb et al., 1994). At the lab, a subsampling technique was applied to assess mas sive flying aphids collected on the yellow sticky cards by randomly selected six small squares on each side of the yellow card which was beforehand wrap ping with a transparent paper (Figure 3 .5) (Liburd et al., 2009). This sampling tactic excludes
82 errors f rom counting and decreases the time allocated per trap (Liburd et al., 2009). A 40X electronic microscope was used to identify microscopic insects. Statistical Analysis Data from all sampling strategies were analyzed using repeated measures analysis (PROC GLIMMIX, SAS 9.3, version 2006 2010 by SAS Institute Inc., Cary, NC, USA) in order to determine mean effects of cover crops planting, fertilizer, and tillage management as well as their possible interactions. Means separation was performed using least squ ares means (LSMeans). Results were considered significant at P Results and Discussion Effect of Cover Crops and Tillage on Insect Populations from Pitfall T raps Species collected in the pitfall traps were predominantly natural enemies during both gr owing seasons. Groups of species captured included spiders ( Oxyopidae Licosidae and A raneae ), fire ants (FA), wasps (mostly Braconidae Aphidiidae and T richogrammatidae ), syrphid flies (SF) particularly hover flies, and ground beetles ( Carabidea and Staph ynilidae ). Aphids, including green peach ( Myzus persicae ) and turnip ( Lipaphis erysimi ) were the only insect pests recorded from pitfall traps during the experiment. Statistical analysis revealed no interactions between cover crops planting, fertilizer, a (GB) in fall 2011 and FA in fall 2012; respectively, where a two way interaction between fertility and tillage was recorded (Table 3 3). A significantly greater number of SF and a phids were recorded in fall 2011 in sorghum sudangrass subplots compared to other treatments. Syrphid flies were found in significant number as well in fertilized plots in fall 2011. Aphid populations were greater in fertilized plots in fall 2012. This may be due to
83 the decrease of SF population in these plots compared to fall 2011growing season (Table 3 4). However, there was a general tendency in both years for SF populations to be greater in plots where aphid populations were also greater. This may be ex plained by the affinity of SF species to feed on aphids. In conjunction with that trend, Tumlinson et al. (1993 ) reported that when crop s are attacked by pest s they transmit chemical signals that attract beneficial insects A predominance of aphids in tr ansplanted cabbage was observed mainly before heading, an observation also noted by Mossler et al. ( 2011). These authors reported that green peach aphids are attracted to cabbage immediately prior to heading. It is important to notice that the greatest num ber of syrphid flies were observed where the aphid population was greater but seemed to be insufficient to regulate aphid density (improperly density related factor; MC neill et al., 2012 ). Spiders were abundant within NT subplots, and were present in grea ter numbers than CT (Table 3 4). The strong occurrence of natural enemies in pitfall traps in cabbage may be due to the presence of decaying cover crop residues. Effect of Fertilizer and T illage on GB a nd FA P opulations The addition of fertilizer to cover crops affected GB populations during fall and the FA population during fall 2012. Ground beetle populations were greater in NT fertilized plots. However, there was no significant difference between GB populations in NT and CT unfertilized subplots and fert ilized CT subplots (Table 3 5). This result showed that ground beetles were more active in cropping systems involving residue mulches. This observation is in acco rdance with Eyre et al. (2009) who reported that some ground beetles species were significan tly more active in weedier fields Prasifkaet al. (2006) also found that living mulches increased the occurrence of GB population s and improved predation within corn soybean forage rotation systems.
84 Fire ant population s w ere significantly greater in unfer tilized NT sub plots compared to unfertilized CT subplots (Table 3 5). This observation is supported by previous reports that ground dwelling species prefer botanically diverse ( weedy ) environments. Although cultural techniques and sampling strategy were th e same within CT plots and NT plots, this tendency for ground insect populations from pitfall traps to be greater in NT plots than CT plots is consistent with previous research conducted in this area that document s a general trend for ground dwelling speci es to have affinity with weedy fields or systems with soil surface residues Effect of Cover Crops and Tillage on Insect Populations from Yellow Sticky T raps Insect populations captured from active yellow sticky cards (YSC) included the pest diamondback m oth (DBM), and beneficial lady bugs (LB), wasps and SF in fall 2011. In addition to species recorded during the previous season, adult flying aphids and damsel bugs (DB) were also captured during fall 2012. There was no interaction effects of treatments on pests or beneficial populations recorded from the yellow sticky traps (Table 3 3). In both years, any of the treatments significantly affected pest or beneficial insect populations except for SF in fall 2012 when a significant greater number was recorded in CT plots compared to NT plots (Table.3 6). This behavioral trend observed among yellow sticky card insect data may be attributed to the absence of a buffer zone between treatment plots, and that flying insects may easily move from one plot to another a t any given time. Except for SS NT plots, Aphid population means were inversely higher within NT and CT plots (Table 3 6) within yellow sticky cards compared to results obtained with pitfall traps (Table 3 4) and in situ counts (Table 3 7); respectively. Based on that observation, it could be attested that this inconsistency concerning the results obtained from yellow sticky cards in
85 comparison with the two others sampling strategies may be explained by the following reasons: 1. There was no buffer zone separating CT and NT plot which means insects could intentionally fly from one plot to another; 2. There was a periodical wind blowing during sampling dates for both years meaning as a result, insect s could unintentionally travel over the neighbor and ad jacent plots; and 3. Concerning aphids particularly, a subsampling technique was applied during the counting procedure where 6 squares from each side of the YSC were randomly which ma y to a lesser extent played on the results as well. These results consisting of a non significant effects of treatments obtained on insect populations captured with YST were similar to those obtained by Bhan in 2007 and 2008 respectively using the same sa mpling technique to monitor aphids and whitefly populations under cover crops and intercropping growing systems in organically grown sweet corn and bell pepper in Florida (Bhan, 2010) Effect of Cover Crops and Tillage on Insect P opulations from in Situ C o unt In situ count (ISC) sampling strategy was carried out on every insect found on cabbage leaves during all sampling times. However, statistical analysis was performed uniquely on species that showed a relatively analyzable number. Aphids. In 2011, aphi d populations were not significantly different within cover crops and fertilized plots. However, SS and SP had higher number of aphids than PP and NC. In fall 2012, aphid population was significantly higher in SS plots than PP plots. SP and unfertilized pl ot however showed higher mean than NC plots. For both years, aphid populations were significantly higher within NT plots than CT plots ( T able 4 7). The highest aphid numbers, in both years were recorded in SS and SP plots. This is obvious, in view of the f act that SS is well known as a tolerant plant species for aphids.
86 In comparison with other grass species evaluated, Rustamani and Kanehisa (1992) reported that sorghum in general tend to tolerate aphids due to their low aconitic acid (less than 200 g/wet weight) considered as moderate anti feedent to aphids. Results obtained from ISC showed consistency with results obtained with aphids from the pitfall trap sampling strategy (Table 3 4 and 3 7). Sorghum sudangrass subplots were associated with more aphids than SP subplots. This is in accordance with results obtained during 2007 and 2008 by Bhan who observed that within the summer cover crop mixtures of sorghum sudangrass and velvetbean, aphids, thrips and whitefly populations were less than the other tream entsin sweet corn and bell pepper (Bhan, 2010) Whitefl ies. In both years, whitefly was not a problem in comparison with aphids. No significant difference was recorded in any treatment in both years. In the first year, all treatments displayed similar aver age numbers of whitefly. However, during the second year, the greatest number of whitefly was recorded within SP, fertilized and unfertilized plots and CT plots (Table 3 7). This result suggests that PP and SS reduced whitefly numbers more than other treat ments in fall 2012. The lowest whitefly counts observed in SS plots is in accordance with results found with SS by McNeill et al. (2012) on effects of cover crops on aphids and whiteflies. It is hard to explain this change observed in whitefly population b etween treatments in fall 2012. However, it may be attributed to a possible uneven distribution of whitefly movement during that specific growing season. Also, the non significance difference observed on whitefly populations during both year between treat ments is corroborated by Bhan (2009) in a research
87 conducted on cover crops included SS on whitefly population in sweet corn and bell pepper (Bhan, 2010) Conclusion s In summary it is obvious that pigeon pea and sorghum sudangrass summer cover crop residu e biomass, when either incorporated by tillage or laid on the soil surface as mulches, may change population of som e key cabbage pests such as aphids as well as some associated natural enemies such as syrphid flies, spiders, ground beetles, and fire ants t o a lesser extent. However, we do not have sufficient evidence to attest that change would be resulted in pest suppression in cabbage based on the non significant presence of DBM population and the relative abundance of natural enemies considering that sev eral parameters such temperature, soil fertility and quality, plant antixenosis, antibiosis and tolerance properties may also contribute to slowing down insect populations. It is also important to point out that aphids accounting among key cabbage pests in Florida were found in significant number over both growing seasons within most of the treatment. However, only pigeon pea among cover crops planting showing the lowest number of aphids during both years. Therefore, we can come up with the assumption that although more data is necessary before advancing any solid recommendation, growers dealing with organic and sustainable vegetable production could be willing to use pigeon pea as cover crop in their production systems in the agro ecosystems where aphids would be considered as a frequent insect pest. At the same time, having regard to the lowest number of whitefly in sorghum sudangrass although not significant in comparison with the other treatments, we may advance that a special regard could be attributed to sorghum sudangrass in an agro ecosystem where whitefly would be a
88 problem. These results also suggest that the cover crops used could harbor important insect predators and parasitoids for vegetable production in general and cabbage in particular. At la st, this study could serve as beginnings to any organic and sustainable vegetable production schemes in tropical and subtropical environments where insect pests constantly remain an issue.
89 Table 3 1 Cover crops repartition and seeding rate establis hment for summer 2011 and 2012 growing seasons in Live Oak Florida Growing season Pigeon pea (PP) Sorghum sudangrass (SS) Mixture PP SS 2011 50 20 25 10 2012 50 40 25 20
90 Figure 3 1 Sketch of the split split plot design of the experiment laid out in Live Oak, Florida
91 Table 3 2. Main effect treatments arrangement according to the experimental design established during growing season 2011 and 2012 in Live Oak Florida. z Even numbers correspond to no till and odd numbers to tillage. NC: no cover (control); PP: pigeon pea (legume); SS: sorghum sudangra ss (grass); SP: mixture b/w PP and SS. Treatment Z Cover Crop y Fertilization x Tillage Methods w 1 NC Y CT NC N CT 2 NC Y NT NC N NT 3 PP Y CT PP N CT 4 PP Y NT PP N NT 5 SS Y CT SS N CT 6 SS Y NT SS N NT 7 SP Y CT SP N CT 8 SP Y NT SP N NT
92 Figure 3 2 Sampling methods used during the experiment for both years. A) Unbaited yellow sticky card setting up at a height contained between 0.30 1m; B) pitfall trap put in the groun d with top end level with the soil surface; C) In situ count scouting for pests; D) a view of the experiment after traps installation.
93 Figure 3 3 A) Stand point where systematic visual counting had lieu every other week; B) Gridded used to count aphids on unbaited yellow sticky traps.
94 Table 3 3. Analysis of variance summary for beneficial and insect pest populations as affected by cover crops mulches, fertilizer and tillage during fall 2011 and 2012 growing seaso ns. Season Main effects d.f. Pitfall traps x Yellow traps y In situ count z SP FA W SF A GB LB DB W SF A DBM WF A Fall 2011 Planting1 3 NS NS NS ** *** NS NS NS NS NS NS NS NS NS Fertilization 1 NS NS NS NS NS NS NS NS NS NS NS NS NS Land P 1 NS NS NS NS NS NS NS NS NS NS NS NS Planting x Land P 3 NS NS NS NS NS NS NS NS NS NS NS NS NS NS Planting x F ert. 3 NS NS NS NS NS NS NS NS NS NS NS NS NS NS Land P x Fert 1 NS NS NS NS NS *** NS NS NS NS NS NS NS NS Plant. x Land x Fert. 3 NS NS NS NS NS NS NS NS NS NS NS NS NS NS Fall 2012 Planting1 3 NS NS NS NS NS NS NS NS NS NS NS NS NS NS Fertilization 1 NS NS NS NS NS NS NS NS NS NS NS NS NS Land P 1 NS NS NS NS NS NS NS NS NS *** NS NS NS Planting x Land P 3 NS NS NS NS NS NS NS NS NS NS NS NS NS N S Planting x Fert. 3 NS NS NS NS NS NS NS NS NS NS NS NS NS NS Land P x Fert 1 NS *** NS NS NS NS NS NS NS NS NS NS NS NS Plant. x Land x Fert. 3 NS NS NS NS NS NS NS NS NS NS NS NS NS NS x SP= spiders; FA= fire a nts; W= wasps; A= aphids; GB= ground beetles; y LB= lady beetles; DB= damsel bugs; DBM= diamondback moth; z WF= whitefly. *, **, and *** Significant at P< 0.05, 01, and 0.001 respectively
95 Table 3 4. Effect of Cover crops, fertilizer, and tillage on insect pest and beneficial populations captured in cabbage from passive pitfall traps during fall 2011 and 2012 growing seasons. Mean SEM no. insects per pitfall trap in cabb age for all sampling dates; Mean SEM no. insects per pitfall trap in cabb age for all sampling dates Spiders Fall 2011 Syrphid Aphids Spiders Fall 2012 Syrphid Aphids Main effects Fire A. Wasps Ground Wasps Flies beetles Flies Cover crops treat. Pigeon pea 1.10.2 4.4 1.3 1.10.2 0.40.1b 0.10.1ab 1.30.3 0.70.1 0.71.8 0.30.1 0.90.3 Sorghum S. 1.00.2 3.81.3 1.30.2 0.90.1a 0.30.1 a 1.00.3 0.70.1 4.01.8 0.10.1 1.30.3 Mixture 0.80.2 5.51.3 0.70.2 0.50.1b 0.20.1ab 1.70.3 0.50.1 1.41.8 0.50.1 1. 30.3 Control 0.80.2 4.91.3 1.30.2 0.50.1b 0.00.1 b 1.00.3 0.70.1 0.51.8 0.30.1 1.30.3 P value 1 0.3062 0.7937 0.3569 0.0140 0.0013 0.3380 0.3311 0.4865 0.3465 0.5979 Fertilization treat. Yes 0.90.1 4.20.8 1.20.1 0.70.1a 0.2 0.0 1.30.2 0.60.1 2.71.3 0.20.1 0.90.2b No 1.00.1 5.20.8 1.00.1 0.50.1b 0.20.0 1.20.2 0.70.1 0.51.3 0.30.1 1.60.2a P value 0.5680 0.3550 0.1254 0.0457 0.7571 0.6411 0.1228 0.2145 0.2935 0.0048 Tillage treatment Till 0.80.1 b 4.00.8 1.10.1 0.60.1 0.10.0 1.30.2 0.70.1 2.81.3 0.30.1 1.10.2 No till 1.10.1a 5.30.8 1.20.1 0.70.1 0.20.0 1.20.2 0.60.1 0.51.3 0.20.1 1.40.2 P value 0.0320 0.2600 0.5245 0.1761 0.1228 0.6766 0.3304 0.2032 0.3940 0.2679 50lbs o f N/acre (57 kg /ha) applied week 4 after cover crops emerg ence; 1 Mean separation within colunms by Student's Least S quares Means followed by the same letter are not significantly different
96 Table 3 5. Effect of ferti lizer, and tillage on ground beetles and fire ants populations captured in cabbage from passive pitfall traps during fall 2011 and 2012 growing seasons. Mean SEM no. insects per pitfall trap in cabb age for all sampling dates 1 Ground beetle (ground and rove beetles); 2 fire a nts. Mean within rows having same uppercase letters and means within columns having same lowercase letters are not GB 1 / fall 2011 FA 2 / fall 2012 Main effect 57kg ha 1 N 0 kg ha 1 N 57kg ha 1 N 0 kg ha 1 N Till 0.31.8 Ab 0.41.8 Ab 12.11.8 Aa 6.91.8 Bb No till 1.21.8 Aa 0.41.8 Bb 9.11.8 ABab 13.51.8 Aa
97 Table 3 6. Effect of Cover crops, fertilizer, and tillage on insect pest and beneficial populations captured in cabbage from active yellow sticky traps during fall 2011 and 2012 growing seasons. Me an SEM no. insects per yellow sticky trap in cabb age for all sampling dates 50lbs of N/acre (57 kg /ha) applied week 4 after cover crops emerg ence; 1 Diamondback moth; 2 Mean separation within colunms by Student's Least S quares Means followed by the same letter are not significantly different DBM 1 Fall 2011 Syrphid Aphids Fall 20 12 Syrphid Main effects Lady B. Wasps DBM Wasps Damsel Flies bugs Flies Cover crops Pigeon pea 0.40.7 0.30.9 1.90.3 0.50.1 0.10.0 1.40.2 0.10.0 0.90.2 0.50.2 Sorghum sudangrass 0.20.7 0.30.9 2.00.3 0.70. 1 0.10.0 1.30.2 0.00.0 1.00.2 0.80.2 Mixture 0.20.7 0.40.9 2.10.3 0.70.1 0.10.0 1.40.2 0.10.0 1.10.2 0.90.2 Control 0.20.7 0.40.9 2.10.3 0.60.1 0.10.0 1.40.2 0.10.0 1.00.2 0.80.2 P value 2 0.4501 0.5463 0.8937 0.6517 0.7668 0.9 702 0.7232 0.9138 0.4140 Fertilization Yes 0.30.5 0.40.6 2.20.2 0.60.1 0.10.0 1.40.2 0.10.0 1.00.1 0.90.1 No 0.20.5 0.30.6 2.00.2 0.60.1 0.00.0 1.30.2 0.10.0 1.00.1 0.70.1 P value 0.7921 0.3360 0.2245 0.9582 0.1241 0.76 59 0.5067 0.9733 0.1639 Tillage Till 0.30.5 0.30.6 2.00.2 0.60.1 0.10.0 1.50.2 0.10.0 1.20.1 1.00.1a No till 0.30.7 0.40.6 2.00.2 0.60.1 0.10.0 1.20.2 0.10.0 0.80.1 0.50.1b P value 0.4472 0.1093 0.5911 0.8751 0.5378 0.2 341 0.7398 0.0668 0.0007
98 Table 3 7. Effect of Cover crops, fertilizer, and tillage on insect pest and beneficial populations captured in cabbage from in situ count during fall 2011 and 2012 growing seasons. Mean SEM no. insects per sample of 5cabbage plants for all sampling dates Fall 2011 Fall 2012 Main effects Aphids Whitefly Aphids Whitefly Cover crops Pigeon pea 0.00.2 0.10.1 11 .96.5 b 0.30.2 Sorghum sudangrass 0.30.2 0.10.1 33.56.5 a 0.20.2 Mixture 0.30.2 0.10.1 22.06.5 ab 0.40.2 Control x 0.20.2 0.10.8 20.26.5 ab 0.50.2 P value y 0.7636 0.9632 0.1372 0.6437 Fertilization Yes y 0.10.1 0.10.1 16.64. 6 0.40.1 No 0.20.1 0.10.1 27.24.6 0.40.1 P value 0.4840 0.2897 0.1056 0.8516 Tillage Till 0.10.1 b 0.10.1 14.84.6 b 0.40.1 No till 0.40.13 a 0.10.1 28.94.6 a 0.30.1 P value 0.0277 1.0000 0.0307 0.3759 50lbs of N/acre (57 kg /ha) applied week 4 after cover crops emerg ence; 1 Mean separation within colunms by Student's Least S quares Means (LSMeans) test at Means followed by the same letter are not significantly different
99 CHAPTER 4 CONCLUSION S The main objective of this research was to identify the best cover crop planting and management strategy that is sui table for optimizing vegetable production in tropical environments. Specifically, it aimed at, on one hand, evaluating effects of grass legume planting arrangement and tillage method (cover crop termination method) on yield of subsequent cash crop And on the other hand, determining how the cover crop planting arrangement and tillage method influences key insect pest and beneficial populations. To achieve these purposes, two summer cover crops, pigeon pea, Cajanus cajan L. and sorghum sudangrass hybrid, Sor ghum bicolor var. Sudanense were for that end evaluated. The effect of cover crop on yield of subsequent cash crop has been well documented in conservation tillage in both organic and sustainable production. However, those researches have been conducted mo stly on agronomic crops than vegetable crops and much more in temperate climates than subtropical and tropical agro ecosystems. This research provid ed insights on subsequent effects of these two summer cover crops on yield as well as insects populations of subsequent cash crops in subtropical and tropical farming systems. Results showed that out of low air temperature conditions, farming systems involving a combination of sorghum sudangrass and pigeon pea could be promising for growers in the tropics consi dering growing organic or sustainable vegetables. Under adequate temperature conditions, pigeon pea can produce high biomass residue for conservation tillage production systems. Results from this research showed that pigeon pea was the best cover crop to i ntegrate in sustainable vegetable production systems.
100 From the point of view of conservation tillage, all considered, pigeon pea was the best cover crop species among those evaluated to integrate within conservation tillage vegetable production schemes. F rom a tillage perspective in general, cabbage yields were better when cover crop residues were incorporated into the soil. Another interesting aspect of the results was residues biomass previously fertilized before incorporated by tillage resulted in great est yield in every case except with sorghum sudangrass during the second year of the experiment the opposite was recorded. Also, with yield of subsequent cash crop was not tillage dependent only when fertilized pigeon pea residues were used. On the IMP asp ect of the research, a lot of beneficial insect populations were harbored during the growing seasons. Dimondback moth, a potential pest for cabbage was not found in significant number during the growing season. However, aphids which are also cabbage key pe st in Florida were found in significant numbers on the other side during plots. Thus, growers in the tropics growing vegetables that are susceptible to aphids should avoid u tilized sorghum sudangrass as cover crops. Pigeon pea would be a better alternative in that case. At last, this study could serve as beginnings to any organic and sustainable vegetable production schemes in tropical and subtropical environments where insec t pests constantly remain an issue. Overall, In Tropical farming systems, like in the Caribbean where the climate is more or less constant, No ti ll vegetable production with pigeon pea and biculture between pigeon pea and sorghum sudan grass as cover crop could be promising.
101 Further study is needed to evaluate pigeon pea potentiality in comparison with other summer legume cover crops commonly used throughout the south both in no till and conventional vegetable farming.
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114 BIOGRAPHICAL SKETCH Dakson Sanon was born in Aquin, South Haiti. He is father of a beautiful 4 year old girl named Daknishael Bezaleel Sanon. Dakson did his Bachelor of Science in a gronomy in 2003 at State university of Haiti. He did two in service training in Israel back to Aquin and began w orking for Agronomist and Veterinarians without Borders (AVSF) as Assistant Coordinator of a Project for Production and Marketing of Fruit. In 2007, Dakson contributed to introducing new cultivars of watermelon and eggplant seeds in the agro ecosystems of Aquin. From 2007 to 2009 he worked for Funds for Economic and Social Assistance as an a gronomist responsible for implemented economic project in rural communities. Before granting the scholarship to start his n hired as extension agent for Ministry of organizations in the southern region of Haiti. includes promoting and improving organic and sustainable agriculture in the south.