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1 DETERMINING THE AGRONOMIC AND PH YSIOLOGICAL CHARACTERISTICS OF THE CASTOR PLANT (RICINUS COMMUNIS L.): DEVELOPING A SUSTAINABLE CROPPING SYSTEM FOR FLORIDA By DAVID NEIL CAMPBELL A THESIS PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORID A IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE UNIVERSITY OF FLORIDA 2013
2 2013 David Neil Campbell
3 To my Wife and Loving Family
4 ACKNOWLEDGMENTS Firstly I would like to thank the Universi ty of Florida, IFAS and Dr. Rowland for giving me the opportunity to continue my education in possibly one of the most important fields, Agronomy. I would like to thank Dr. Diane Rowland for her knowledge, continued guidance and encour agement; Dr. Schnell for his cropping system and offsite support; Dr. Jason Ferrell for his in-depth analysis and intellectual curiosity; Dr. Ann Wilkie for her bioenergy enthusiasm and outsi de perspective; and Dr. Jerry Bennett for his generous time commitments and dedication to graduate student excellence. I would like to thank Dr. Arnold Saxton for his statisti cal assistance. I would like to thank Dr. Dick Auld for providing the seeds and conti nued consultation throughout the project. I am grateful for the advice and reliability of Jim Boyer, PSREU Research Coordinator, the farm managers at the WFREC, staff at PSREU and WFREC, and the many inmates that helped with field work. I could not have completed this project without the help from my colleagues and co-workers and would li ke to give a special recognition (in alphabetical order) to Seth Byrd, Adam Cook, Blaire Co lvin, Scott Edmundson, Megan Mears, Justin Mize, Bishow Poudel, Andy Schreffler, Cody Smith, Josh Thompson, and Reggie Toussaint. Finally, I would like to t hank my family for their continued support and especially my lovely wife, Catherine. Without her suppor t I would not have been able to complete this degree and I am gratef ul for her editorial and emotional support.
5 TABLE OF CONTENTS page ACKNOWLEDG MENTS .................................................................................................. 4LIST OF TABLES ............................................................................................................ 7LIST OF FI GURES .......................................................................................................... 8LIST OF ABBR EVIATIONS ............................................................................................. 9ABSTRACT ................................................................................................................... 11 CHAPTER 1 LITERATURE REVIEW .......................................................................................... 13Prospects of Castor Cult ivation in Florida ............................................................... 13Botanical and Agronomic Char acteristics of Castor ................................................ 16Cropping System Considerations for Castor in Florida ........................................... 192 EFFECTS OF PLANT GROWTH RE GULATOR, CULTIVAR, AND HARVEST AID ON CASTOR PRODUCT ION IN FL ORIDA ..................................................... 30Chapter Abst ract ..................................................................................................... 30Introducti on ............................................................................................................. 31Materials and Methods ............................................................................................ 34Field Preparation and Crop Maint enance ......................................................... 34Plant Growth Regulator .............................................................................. 35Harvest Aid ................................................................................................ 36Yield, 100 Seed Weight and Oil Perc entage .............................................. 36Phenological and Physiolo gical Measur ements ............................................... 37Season long m easurement s ...................................................................... 37Physiological responses to PGR applic ation .............................................. 38Statistical A nalysis ............................................................................................ 39Results .................................................................................................................... 40Yield, 100 Seed Weight and Oil Perc entage .................................................... 40Phenological and Physiolo gical Measur ements ............................................... 41Physiological responses to PGR applic ation .............................................. 42Effectiveness of Harves t Aid treat ment ...................................................... 43Discussio n .............................................................................................................. 573 ASSESSING SAP FLOW RATES AND DETERMINING KC CURVES FOR CASTOR PRODUCTION IN FLOR IDA ................................................................... 63Chapter Abst ract ..................................................................................................... 63Introducti on ............................................................................................................. 64
6 Materials and Methods ............................................................................................ 67Field Preparation and Crop Maint enance ......................................................... 67Soil Evaporation Measurement s and Data Analysis ......................................... 68Sap Flow and Meteorological Meas urements and Data Analysis ..................... 68Results and Discussion ........................................................................................... 714 SUMMARY ............................................................................................................. 80LIST OF RE FERENCES ............................................................................................... 83BIOGRAPHICAL SKETCH ............................................................................................ 90
7 LIST OF TABLES Table page 1-1 2010 average castor seed production area, seed yield, and total seed production in ten major producin g countries wo rldwide ...................................... 291-2 Yields across US regi ons from 1 941 to 2003...................................................... 292-1 ANOVA of Yield, 100 Seed Weight and Oil Percentage. F values for treatment effects on oil percent age in PSREU and WFREC in 2011 .................. 442-2 Mean values for Yield, 100 Seed Weight and Perc ent of Oil .............................. 442-3 ANOVA of Nodes to First Raceme. F values for treatment effects on LAI in PSREU and WFREC in 2011 and 2012 ............................................................. 452-4 Mean values for nodes below first raceme ......................................................... 452-5 ANOVA of Racemes. .......................................................................................... 452-6 ANOVA of LAI. .................................................................................................. 452-7 ANOVA of Height. ............................................................................................. 462-8 ANOVA of Root Ar chitecture ........................................................................... 462-9 ANOVA of leaf level ph ysiological tr aits. .......................................................... 472-10 Mean values for Photosynthetic Effects on Brigham in PSREU in 2011 and 2012 ................................................................................................................... 482-11 ANOVA of Post Harv est Aid Appl ication ............................................................. 493-1 Sap Flow Regre ssion of 2011 and 2012. ............................................................ 753-2 Florida 10-day Kc Av erage ................................................................................. 753-3 Florida Kc Values bas ed on FAO Time frames ................................................... 76
8 LIST OF FIGURES Figure page 2-1 PSREU 2012 Weekly yield colle ction ................................................................. 502-2 Total Number of Race mes .................................................................................. 512-3 Leaf Area Index. ................................................................................................. 522-4 Plant height ........................................................................................................ 532-5 Root Length by soil depth zone .......................................................................... 542-6 Root surface area by soil depth zoneP. .............................................................. 552-7 Harvest Aid effects in PSREU 2011 and PR SEU 2012. ..................................... 563-1 2012 Daily versus Histori cal Solar Radi ation. ..................................................... 763-2 Average daily s ap flow ra tes ............................................................................... 763-3 Average daily so lar radiat ion .............................................................................. 773-4 Seasonal Sap Flow and ETo meas urement s ..................................................... 783-5 Regression of crop wa ter flow per area .............................................................. 783-6 10 Day Average Kc Values and ETo ................................................................... 79
9 LIST OF ABBREVIATIONS ai Active ingredient AOAC Association of Offici al Analytical Chemists, now AOAC International Ci CO2 concentration inside the leaf Cv. Cultivar DAP Days after planting DAT Days after treatment DOY Day of year, Julian calendar ETc Crop evapotranspiration ETo Reference evapotranspiration E Evaporation FAO Food and Agriculture Organization of the United Nations FAWN Florida Automated Weather Network Fv/Fm Variable chlorophyll fluore scence over maximum chlorophyll fluorescence measures photosynthetic efficiency HA Harvest aid Kc Crop coefficient LAI Leaf area Index PGRs Plant growth regulators Pn Photosynthesis PSREU Plant Science Research and Educ ation Unit, University of Florida RWC Relative water content SPAD Special Products Analysis Divis ion (a division of Minolta) SLA Specific leaf area Tc Crop transpiration US United States of America
10 WFREC West Florida Research and Educ ation Unit, University of Florida
11 Abstract of Thesis Pres ented to the Graduate School of the University of Florida in Partial Fulf illment of the Requirements for t he Degree of Master of Science DETERMINING THE AGRONOMIC AND PH YSIOLOGICAL CHARACTERISTICS OF THE CASTOR PLANT (RICINUS COMMUNIS L.): DEVELOPING A SUSTAINABLE CROPPING SYSTEM FOR FLORIDA By David Neil Campbell May 2013 Chair: Diane Rowland Major: Agronomy Castor ( Ricinus communis L.) oil is valuable comm odity for the US government and private industries and currently all castor oil is imported. In order to promote domestic castor production, research on cro pping systems throughout the US is needed to determine regions and management system s that are able to support sustainable production of the crop. Effective contro l of excessive vegetative growth, crop termination, and efficient water use are nec essary system components for production in a semi-tropical environment such as Florida. To ex plore Florida cropping system components, research was conducted in t he north central and panhandle regions. For two castor cultivars, yiel d, phenological characteristi cs, root architecture, and physiological traits were studied in response to a plant growth regulator and harvest aid, and a crop coefficient for irrigation management was developed. Castor yields, seed weights, and oil percentages we re lower than production repor ts from southwestern US regions, possibly linked to increased diseas e presence in Florida. While the plant growth regulator was ineffective in c ontrolling plant height, one harvest aid was successful at terminating and defoliating the crop in the absence of a freeze. Crop
12 water use was measured with sap flow collars and appropriate Kc values were determined for efficient irrigat ion practices for castor grown in Florida. This study demonstrated that a castor production system is possible in Florida but yield potential is limited, likely due to increased disease pressure.
13 CHAPTER 1 LITERATURE REVIEW Prospects of Castor Cu ltivation in Florida Evidence of castor seeds in tombs as ear ly as 4000 B.C. (Weiss, 1971) suggests that castor oil has been a valuable commodity throughout mu ch, if not all, of human history with scholars projecting a much earlier date of cultivat ion. The oil is still used today and is considered a strategic material for national defense for use as a lubricant for military equipment in the United States of America (US). Currently commercial domestic production does not exist, but previ ous research efforts have shown that castor can be grown domestically with yields at and above reported international yields. Therefore, agricultural states such as Florida, should conduct preliminary tests to determine the feasibility of production to me et strategic needs and ex plore the potential for domestic production. Castor oil was historically used as a purgative, skin ointment, and lamp oil (Weiss, 2000). Castor oil is in high demand because it can be chemically broken down into unique subunits which are incorporated in a variety of marketable goods such as paint, coatings, inks, lubricants and a wide variety of other products (Ogunniyi, 2006). In addition, its high oil content (48.2% o il by weight) (Wang et al., 2010) makes it an attractive crop of choice for farmers. India, China, Brazil and Mozambique currently lead the world in castor production, with Par aguay, Thailand, Ethiopia, Angola, Vietnam, and South Africa contributing relative ly minor amounts (FAOSTAT, 2013). Manufacturers and companies in the US almost exclusively purchase castor from India because India contributes approximately 90% of the total inter national export trade market (Kumar, 2012). In 2010, world castor production exceeded one million tons, with
14 an average yield of 999 kg ha-1 (Table 1-1). Although t he US does not currently commercially produce castor oil, it has been repor ted that yields of ir rigated castor from Texas range from 2,242 to 3,363 kg ha-1, with some fields producing 4,035 kg ha-1 (Brigham, 1993), indicating that the US potential yield c ould easily exceed existing global yields. Although the US is not currently invest ed in commercial production of castor, there has been a history of US production du ring World War I (WWI ) and World War II (WWII) with preliminary research on castor in Florida as early as 1917 (Rolfs, 1917). Due to the high viscosity of t he oil, the US military found t hat castor oil was especially useful in hydraulic fluids, greases, and lubric ants for military equipmen t. As a result, the US government started initiative s to explore the feasibility of growing castor in the US and later passed legislation to officially rec ognize the importance of castor oil for wartime needs. In 1984, congress passed Agricu ltural Materials Act P.L. 98-284 which classified castor oil as a st rategic material and Public Law 81-774 requires that strategic materials be acquired and stored in the US fo r national defense pu rposes (Roetheli et al. 1991). The US is required to keep 5 million pounds of cast or oil with stocks managed by the Department of Defense (Congre ss, 1991). Attempts to grow castor domestically started as early as the 1850s, but until the early 1900s varieties were excessively tall, prone to shattering, and har vested by hand. Agronomic efforts during WWI identified the most productive castor cultivation area as an oval-shaped area extending from the Panhandle of Texas on the Southwest to t he southern tip of Ohio on the Northeast. This area was delineated on the West by too little rainfall, on the North by
15 too few frost-free days, and on the South and Ea st by a disease hazard resulting from excessive rainfall and humid ity (Domingo, 1953). A collaboration between the Baker Castor Oil Company and the US government advanced castor breeding and cultivation effo rts especially during WWII by improving site and cultivar (Cv.) selections. Connor Doughty II, and Kentucky 38 were the highest yielding cultivars without irrigation wit h the highest yields above 2,390 kg ha-1 (Table 12). By comparison, in the same study yields from the same cultiv ars grown in Florida never exceeded 766 kg ha-1 (Table 1-2). In 1943, approxim ately 2,428 ha of castor was grown domestically (Domingo, 1953), and the pr oduction area rose dramatically to over 19,830 ha by 1951. In the 1960s, Texas alone had over 29,947 ha in castor production (Brigham, 1993). But in 1972, castor produc tion stopped due to a confluence of factors such as: the elimination of government pric e support, low castor oil prices, contractual price disagreements, and compet itive prices for competing crops (Brigham and Spears, 1996). Since then, castor plantings in the US have been largely conducted by academic research units. Currently, one high yielding cultivar grown in Texas, Hale, has yielded an average of 2,242 to 3,363 kg ha-1 with slightly lower yields in the southeastern US (Table 1-2). This prior research has identified high yiel ding castor varietie s, but Florida has historically been considered an undesirable production area fo r castor due to excessive rainfall and humidity bringing increased diseas e pressure. However, with the advent of improved fungicide products, new cultivar s, and improved cropping systems combined with the recent severe drought conditions suffered by many of the highest castor
16 producing areas in the US, the potential of growing this valuable oil seed crop in high precipitation regions of the US, in cluding Florida, should be reexamined. Botanical and Agronomic Characteristics of Castor Castor is an oil seed crop from the Euphorbiaceae family. Castor has been commonly referred to as a "bean" but it is not a legume and is toxic if eaten raw. Most scholars agree that castor or iginated in the tropics of Ethoipia where it grows as a perennial up to 12 m tall and will defoliate a nd die when temperatures reach -4C for four hours (Weiss, 1971). Dwarf cultivars gr own in the Texas High Plains and TransPecos region are 1 to 2 m in height (B righam 1993) as compared to the normalinternode varieties, which range from 1.8 to 3.7 m tall (Brigham, 1970). The cotyledon leaves are oval shaped and directly opposite on the stem, but true leav es are alternately arranged and born on long and sturdy petiole s (Weiss, 1971). The reproductive structure of castor is a raceme, specifical ly a monoecious inflorescence. The raceme usually bears pistillate (female) flowers on the distal (30-50% ) end of the spike and staminate (male) flowers on the proximal (70-50%) end of the spik e. The ratio of pistillate to staminate flowers can vary depending on raceme length and environmental conditions, and hybrids are being developed to increase vigor and pistillate flower counts (Severino et al., 2012). The first, or primary, ra ceme is typically the largest and can be found between the 6th and 16th node with subsequent racemes arising from branches below the primary raceme (Brigham, 1993). It has been observed that two or three branches can occur at the same time or staggered throughout the growing season and as a result, it is likely that a plant will have racemes at each stage of development in the mid to late growing season. Nodal position of the first raceme is important when c onsidering varieties
17 better suited for mechanical cultivation to ensure the combine is built and set to an appropriate height to effectively harvest and capture most, if not all, of the seeds (Weiss, 1971). Pollen is discharged from the anthers and is carried to the stigmas mainly by wind (Brigham and Spears, 1960), but the pr esence of bees and other pollinators in Florida may suggest multiple means of po llination. After pollination, the stamens become dry and fall off, leaving only the pistillate flowers which develop into a spiny or spine-less capsule. Each capsule contains three carpels and each carpel contains a single mottle-patterned seed which varies in color and size depending on the cultivar and region of production. Castor seed is an endospermic dicotyledon and, as opposed to storing oil in the embryo, castor has a sm all embryo and stores o il in liposomes which occupy a large portion of the endosperm of the seed. After maturation, the dried carpels become brown and, as opposed to earlier varieties that forcefully dehisced and scattered seeds, recent dwarf cultivar s have been bred to reduce shatter. Castor is a diploid (2n=20) with few natural polyploids and demonstrates no loss of vigor when self-pollinated (Moshkin, 1986). Approximately 11,300 accessions of castor seed can be found in germplasm banks in 11 countries with the most extensive collections in India, China, Brazil and the US (Severino et al., 2012). Evaluation of and breeding from these accessions has produced two promising varieties: a high oleic acid mutant (Muoz et al., 2004) and low ricin cultiv ars (Auld et al., 2009). High oleic acid mutants are better suited for biodiesel product ion and low ricin varieties are less toxic. Castor naturally produces three toxins: ricin (RCA60), Ricinus communis agglutinin (RCA120), and ricinine (Severino et al., 2012). Ricin is not found in the
18 processed castor oil because it is insoluble in oil, but is retained in the meal after the refining process. Seed maturation takes approximately 44 days and ricin loading begins around 28 days after pollination (Barnes et al., 2009). Ricin is present in the endosperm of the seed until approximately 6 days after the radicle emer ges (Barnes et al., 2009). Because of the high toxicity of ricin (Audi et al., 2005; Balint, 1974) low ricin cultivars inherently result in a reduced risk for grow ers and processers of castor seed and meal. A low ricin cultivar, Brigham, was bred from castor lines t hat originated from the former Soviet Union (Auld et al., 2009). The average ricin content for the Brigham cultivar ranges from 0.10-5.60 mg g-1 (Auld et al., 2009) as co mpared to one of its genetic parents and a commonly studied cultivar, Hale, which averages 12.2 mg g-1 ricin (Pinkerton et al., 1999) Studies on low ricin cultivars are needed as any adoption of castor production will likely be most successf ul with a less toxic cr op that will inherently confer reduced potential health risks for gr owers, processors and those living near processing plants (Garcia-Gonzalez et al., 1999; Raju et al., 2005). The percentage of oil in castor seed is high, ranging from 37.2-60.7% with an average of 48.2% oil by weight when m easured with NMR technology 40C at a resonance frequency of 9.95 MHz (Wang et al ., 2010). By comparison, the soybean the largest cultivated oilseed crop in the USwhich com poses 58% of the world oilseed production in 2010 (Callanan, 20 11), averages only 20% oil in its seed. In standard castor varieties, the oil is over 90% ri cinolenic acid (Sanfor d, 2009) with 900 g kg-1 ricinolenic acid (C18 H34O3; 12-hydroxyl-cis-9-octadecenoic acid) and 30 g kg-1 oleic acid (C18H34O2; octadec-9-enoic acid) (Muoz et al., 2004). Due to the unique chemical structure of ricinolenic acid, the oil c an be easily broken down and introduced into many
19 industrial processes. The oil is extracted from the seed by mechanical and chemical processes resulting in a separat ion of the crude oil fr om the meal (Akpan et al., 2006). The crude oil is processed and used in mult iple forms, for example: hydrogenated oil, dehydrogenated oil, blown oil, cold pressed oil (ACME HARDESTY, 2012), and as a potential feedstock for biodiesel production (Scholz and Nogueira da Silva, 2008). Currently the price for castor oil is higher fo r industrial processes than biodiesel, but the potential for use as a straight vegetable oi l or biodiesel are possible and should be reexamined as cultural and technological advances are achieved (Scholz and Nogueira da Silva, 2008). Castor is a unique plant with the potential to be a pr oductive oilseed crop. Breeding advances have resulted in cultiv ars that are better suited to modern day mechanized production. Although toxic element s of the castor se ed have yet to be completely bred out, we could be optimistic simply due to the high-yielding nature of castor. By starting with a baseline of knowledge r egarding growth patterns, physiological responses to production methods and cultivar responses to regional conditions, researchers can develop more sustainable cropping systems that will be suitable to regional variability. Cropping System Considerations for Castor in Florida Transplanting a crop that originated in the tropics to the semi-tropical environment of Florida will require changes in agronomic management in order to achieve high yields. Tropical plants can live as perennials in their native environment, with hand-harvesting of the seeds occurring multip le times per year, as is the case for some farmers of castor in regions of Africa Perennial cropping syst ems for castor such as this require time-consuming harvests wit h the potential to produce very tall plants
20 with large woody stems (Weiss, 1971). Excessi ve vegetative growth is undesirable for annual cropping systems due to r educed yield and harvest efficiency. In addition, annual crops as compared to perennials need to develop a fully functional root system quicker and irrigation may be required to meet the water needs of a highly productive crop grown in a single season. Therefore, two important growing considerations for developing a sustainable castor cropping syst em in Florida include: (1) control and termination of vegetative growth, and (2) effe ctive water application. However, there has been no research examining these two syst em components in castor production for the state of Florida. To address the first production require ment, the control and termination of vegetative growth, plant growth regulators (P GRs) and harvest aids are likely essential components of a castor cropping system in Fl orida. Although most types of castor planted today are dwarf cultivars, the semi -tropical environment of Florida may still promote excessive vegetative growth. Applic ations of certain PGRs may help control excessive height and internode length and increase the harvest index. Plant Growth Regulators are exogenously applied chemicals that affect plant hormones with the goal of reducing overall canopy growth and inte rnode length. The plant hormone gibberellic acid increases internode length in plants (T aiz and Zeiger, 1998), so many PGRs that function as gibberellic acid inhibitors ar e effective in reducing internode length, especially in cotton (Reddy et al., 1996; Gencso ylu, 2009). However, the castor height reduction efficacy of giberellic acid inhibi tors has been inconclusive in preliminary studies in Texas (Trostle et al., forthcom ing) and effective in others (Ostwalt, 2008),
21 whereas yield reduction is directly correla ted with increased internode length (Stafford, 1971). The semi-tropical temperatures and high rain fall of Florida can also make harvest timing difficult. Mechanical harvest of the cr op would require termination of the crop to insure some level of standard maturity for th is indeterminate crop in Florida. Previous research has shown that harvesting approx imately 10 days after a killing freeze (Brigham, 1993) will result in minimal loss of yield due to shattering. Due to the irregularity of a killing freeze in Florida, research regar ding the effectiveness of a harvest aid may be necessary to ensure maximu m yield. Harvest ai ds are applied with the goal of desiccating and/or defoliating the crop thereby increasing mechanical harvest efficiency and yield. Defoliation percentage, leaf area index (LAI) and leaf browning are good metrics to assess harvest aid effectiveness in cotton (Supak and Snipes, 2000) and are likely to be useful meas urements in castor. Some harvest aids used in the southeast for cotton production ar e tribufos (Supak and Snipes, 2000) and paraquat (Brecke et al., 2001) and are good test candidates for castor production. Due to the lack of information available, it is e ssential that the use of PGRs and harvest aids in a Florida castor cropping system be carefully researched and evaluated. Along with the effect of PGRs and harve st aids, varietal phenotypic expression may differ between the two cultivars of inte rest, Brigham and Hale. Hale and Brigham were registered in 1970 and 2003, respective ly (Brigham, 1970; Auld et al., 2003). Because Hale has been available commerciall y for a longer time, more research has been conducted on the yield potential and general growth habits as opposed to Brigham. Hale is a dwarf cult ivar with the potential for high yields in the US. Original
22 breeding efforts crossing Hale and a known reduced ricin cultivar culminated in the Brigham line which has a r educed RCA 120 and ricin content as well as average heights between 0.3-1.25m (Auld et al., 2003). Research on Hale and Brigham has not been conducted in Florida, and research is needed to determine baseline information on the performance of these cultivars in Florida. Although the semi-tropica l climate of Florida w ould normally provide adequate moisture for successful castor production, there may be some years or periods during the growing season when plant water availabi lity is scarce. Depending on the soil type and rainfall, castor will normally produce the highest yields with supplemental irrigation, but can be grown without it. A study on ca stor conducted in Italy showed a positive response between yield and percent of evapotrans piration (ET) replaced with irrigation (Laureti et al., 1995). Al though the highest yields in this study were achieved with full ET replacement, depending on cost and availability irrigation above 66% ET replacement may not be financially or otherwise desirable. In addition, trials carried out at the same time found the adjusted mean yiel ds of irrigated versus non-irrigated castor grown in the US to be 32 to 49 % higher (Weiss, 2000). Under non-irrigated farming systems in Kansas, Oklahoma, and Texas, castor grew most successfully when exposed to 38-51 cm of rain between Apri l and September (Domingo, 1945). Current research suggests that maximally yielding ca stor has an annual requirement of 20.6 to 24.7 cm ha-1 to produce the highest yields in parts of Texas and can be irrigated every 10-14 days without measureable water stre ss occurring (Brigham, 1993). Because castor yield responds positively to irrigation, a better understanding and quantification of how much water is used th roughout the growing season in Florida will
23 ultimately result in higher yields and r educed water consumpti on. Measuring plant transpiration at full canopy and during optimal conditions (optimum r adiation levels as well as void of water stress, nutrient def iciency, and weed stress) will provide data on water use at peak transpiration times under good agronomic managem ent. Total water used in any agricultural field can be quantif ied as the additive factors of evaporation from the soil surface (E) and transpiration (Tc) of the crop, collectively called evapotranspiration (ETc) (Allen, 1998) (see Equation 1-1) In a one-step procedure, ETc can be calculated and is the pr oduct of a reference ET (ETo) and a crop coefficient (Kc) for different phenological stages (Allen, 1998) (see Equation 1-2). Calculations of ETo vary between location, season and crop chosen. Currently, the standard ETo is based on a hypothetical grass crop in local climatol ogical conditions and is calculated using the Penman-Monteith m odel (Monteith, 1965). Kc values indicate the relative difference in water use between the crop and the reference; for example, a Kc value above 1 indicates that the crop is using mo re water than the reference and Kc values below 1 indicate that the crop is using less water. ETc = E + Tc (1-1) ETc = ETo x Kc (1-2) Growers can collect free ETo values on the Internet fr om the Florida Automated Weather Network (FAWN), which is the co mpilation of information gathered from 37 weather stations across the state (FAWN, 2013). With appropriate Kc values for castor, growers can easily make the one-step ca lculation to determine the crop water requirement and use it to apply supplemental i rrigation above rainfall to meet crop water demand. It is important to note that Kc values are relative to the specific environment (latitude, weather patterns, so il type, etc.) and should only be used for crops grown in
24 similar environments, theref ore making evaluation of Kc values specific for Florida environments essential. Due to the semi-tropical nature of the Florida gro wing conditions, testing a sustainable castor cropping system in this region requires: (1) applying PGRs, (2) applying harvest aids, and (3) evaluating grow th patterns and phenology. In addition, because irrigation is often a component of many Florida farms, it is essential to develop crop coefficients that could be used to irrigat e efficiently in this particular regional climate. Assessing the Physiological Im pacts of Cultural Practices The success or failure of a cropping syst em is usually evaluated solely by analyzing yield differences among treatments. However, truly understanding the causal factors behind yield performance can be evaluated by measuring relevant crop physiological responses to system elements. Evaluating a castor cropping system in Florida would likely include measurem ents of: (1) phenology, canopy, and root architecture development; (2 ) assimilation capacity and efficiency; and, 3) seasonal water use. Of utmost importance is the collect ion of overall phenology and seasonal development of the crop bec ause cropping systems need to effectively control growth patterns in order to maximize yield for a spec ific environment. Research on crop growth has been conducted with many different variet ies of castor in locations outside of Florida with results that are possibly applicab le only to that particular cultivar and /or location. Past research has characterized t he following growth patterns: identification of the highest yielding raceme(s) (Brigham 1993; Weiss, 1971; Russell et al., 2003); optimal growing season length (typically 140 to 160 days; Weiss, 2000); and the optimal
25 height for mechanization (typical ly 0.3-1.25m; Auld et al., 2003). However, none of this information is available for the growing regi ons within Florida; t herefore, phenological assessment of the LAI, total number of racemes and yield of mature racemes throughout the season will provide valuable information for determining optimum harvest times and crop termination to achi eve the highest yield. In addition, an assessment of the root architectural c hanges throughout the season will be useful to determine cultivation and cultivar differences that may provide val uable information for a cropping system. Plant height assessment throughout the growing season will be useful to determine suitability for mechani cal harvesting and effectiveness of PGR application. PGRs may also increase yi eld with the potential for photoassimilate allocation to seed development as opposed to vegetative structure development. Any cultural practice that impacts the phot osynthetic capacity of the crop should be identified because a reduction in photosynt hesis will likely result in a reduction in yield. In addition to controlling height by reducing internode length, PGRs and plant hormones may also affect the photosynthetic capacity of the crop. Zhao and Oosterhuis (1997) found higher stomatal conductance and photosynthesis in water-stressed cotton that was treated with PGR-IV (a plant growth regulator that has been shown to increase yield and growth containing 0.0028% (w/v) gibberellic acid and 0.0030% (w/v) indolebutyric acid). In a later study, Zhao and Oosterhuis (2000) found reduced plant height, improved leaf carbon dioxide exchange rate, and increased leaf starch content of PGR treated plants. Kumar et al. (2001) found that foliar application of giberrellic acid on cotton countered the effects of wa ter stress by increasing photosynthesis, stomatal conductance and transpiration. St omatal conductance and transpiration are
26 inherently linked to photosynthesis due to th e overall gas exchange processes at the leaf level (Taiz and Zeiger, 1998). These pr ocesses can be measured with an infrared gas analyzer (IRGA) that is capable of simultaneously measuring photosynthesis, stomatal conductance, and transpiration (Z obiole et al., 2000; Akhkha et al. 2011; Millan-Almaraz, et al. 2009). Due to the pa ucity of research focusing on the possible side effects of PGRs, this pr oject will include the collection of photosynthetic capacity data after the last PGR appl ication. This data will provide much-needed information regarding the effect of PGRs on photosynt hetic capacity and will help by providing preliminary baseline information for future re search relating to castor production in Florida. In addition to photosynthesis, other related leaf level photosynthetic aspects that might be impacted by PGR application include: chlorophyll fluorescence, chlorophyll content, stomatal conductance, and transpi ration. Chlorophyll fluorescence often increases with stress (Genty et al., 1989; Sc hreiber, 1986). Fv/Fm is a measure of photosynthetic efficiency that decreases with increasing stress (Burke, 2007; Burke, 2010). Chlorophyll amounts are also related to photosynthetic capacity and relative chlorophyll content can be reflected in SPA D chlorophyll meter readings (Bullock and Anderson, 1998; Goffar t et al., 2008). Assessment of crop water use or ETc is another vital pi ece of information for managing water application in general but especially for developing Kc values specifically for the Flori da environment. Determining ETc values has historically been, and is still currently, determined by weighing lysimeters in fields and greenhouses. An alternative method that can be employed in the field uses direct measurements of
27 transpiration and soil evaporation separately (Sakuratani, 1981; Ham et al., 1990). Logged measurements of transpi ration are possible through the use of sap flow technology (Sakuratani and Abe, 1985; Ha m et al., 1990) and measurements of soil evaporation can be carried out in the fiel d using micro-lysimieters (Boast and Robertson, 1982). Plant transpiration collected using the sap flow technology has been proven to be accurate to withi n 10% of the transpiration of the crop when compared to studies utilizing weighing lysimeters (Baker and Bavel, 1987; Smith and Allen, 1996; Hattan et al., 1990). Soil evaporation measur ements using the micro-lysimeter method are reliable when assessing water loss over 1-2 days with measurem ents consistently within a 0.5 mm range (Boast and Robertson, 1982). This study will measure the transpirati on of the castor crop at full canopy coverage in the field under optimal conditions using sap flow collars attached to the stem below all branches of the plant. The collars utilize the heat balance method (Baker and Bavel, 1987) and are indexed to the stem diameter (Smith and Allen, 1996) to determine sap flow. A heating strip (source of the heat pulse) is located between two thermocouples and the difference in temperat ure between the thermocouples is used to calculate total amount of water transpired (Tc). Evaporation (E) can be determined in the field using a mini-lysimeter (Boast and Robertson, 1982) and the combination of E and Tc can result in an ETc measure. Calculated ETo data from FAWN can be related to the measured ETc to determine Kc values. Typically, the growing season is br oken into three primary timeframes characterized by varying Kc values as provided by the Food and Agriculture Organization of the United Nations (FAO). These timeframes, based on phenological
28 observations in the field, include initial, mid, and late season, all of which has a separately calculated Kc value (Allen, 1998). The FA O has published preliminary results for the Kc values for many crops, including ca stor. But, as recommended by the FAO, studies should be conducted in specific environments to determine Kc values that are appropriate for a given location (Allen, 1998). Appropriate cr op coefficients for the highest water use period during the growing s eason will be calculated for castor growing in the north central region of Florida. Summary In conclusion, castor oil has been a valuable resource to humans for over 4,000 years and is still highly prized today. The US has publically stated that the oil is necessary for public defense as a lubricant and various industries have chosen to incorporate the oil as a feedstock for many manufactured goods today. Castor is not currently commercially grown in the US, but past research efforts have shown promise for domestic production. Due to the nati onal need, high yield potential, new and improved cultivars, availabili ty of irrigation, and new cult ural techniques and chemicals, research efforts are needed to develop a sustainable cropping system in agricultural states such as Florida. This research will provide preliminary information needed to develop a sustainable castor cropping system in the State of Florida. The specific research objectives are to: Determine the effect of PGRs on plant height, photosynthetic capacity, yield and other physiological traits of two cu ltivars of castor, Hale and Brigham Determine the effectiveness of harvest ai ds for crop termination by quantifying leaf browning, leaf drop, and LAI on two cultivars of castor, Hale and Brigham Quantify seasonal water use and create a Kc curve for castor in Florida for Brigham
29 Table 1-1 2010 average cast or seed production area, seed yield, and total seed production in ten major produc ing countries worldwide Country Harvested Area 2010 (ha) Yield 2010 (kg/ha) Total Production 2010 (MT) India 910,000 1,2641,149,967 China 210,000 857179,991 Brazil 149,803 62193,028 Mozambique 149,100 25938,602 Paraguay 11,000 1,18213,000 Thailand 12,780 95412,197 Ethiopia 6,800 1,2358,400 Angola 24,800 3027,500 Vietnam 8,000 7506,000 South Africa 7,800 7055,500 World 1,537,773 9991,535,479 Table 1-2 Yields across US regions from 1941 to 2003 Location Latitude Yiel d (kg ha-1) Year Mesa, AZ 1 33.4N 2,390 1942 State College, NM 1 32.5N 2,299 1943 Columbia, TN 1 35.6N 2,270 1941 Columbia, TN 1 35.6N 2,121 1942 State College, NM 1 32.5N 2,036 1942 Tuscon, AZ 1 32.2N 1,981 1941 Mesa, AZ 1 33.4N 1,968 1941 Bard, CA 1 32.8N 1,928 1942 Leesburg, FL 2 28.8N 766 1942 Gainesville, FL 2 29.7N 375 1942 Quincy, FL 2 30.6N 198 1941 Brooksville, FL 2 28.5N 102 1941 Memphis, TN 3 35.1N 1,945 2002 Starkville, MS 3 33.5N 1,944 2002 Shubuta, MS 3 31.9N 1,160 2003 Poplarville, MS 3 30.8N 427 2003 1 Yields above 1900 kg ha-1 (adapted from Domingo, 1945) 2 Yields from Florida (adapted from Domingo, 1945) 3 Highest yields recorded, latitude and year fo r Cv. Hale (adapted from Baldwin et al., 2009)
30 CHAPTER 2 EFFECTS OF PLANT GROW TH REGULATOR, CULTIVAR AND HARVEST AID ON CASTOR PRODUCTION IN FLORIDA Chapter Abstract Castor ( Ricinus communis L.) oil is essential to the US government and private industries for paints, coatings, inks, lubr icants and a wide variety of other products. However, the US must currently import a ll castor oil because there is no commercial scale domestic castor production. Therefore, it is important to develop and research castor cropping systems customized to specific US geographic locations in an effort to establish a domestic source of castor oil and reduce imports. Cropping systems in Florida represent a model of castor producti on in a semi-tropical climate. Effective control of excessive vegetative growth and crop termination with a plant growth regulator (PGR) and harvest aid, respecti vely, will be necessary components in this environment. In an effort to explore components of a sust ainable castor production system in Florida, research was conducted at two locations, Plant Science Research and Education Unit in Citra, FL and West Fl orida Research and Education Center in Jay, FL. Yield components, phenological c haracteristics (height, raceme number, LAI, and root architecture), plant response ( height and photosynthetic capacity) to a mepiquat chloride based PGR and plant response (L AI decrease, leaf browning and leaf defoliation) to different harvest aids were measured. Yields, seed weights, and oil percentages were lower than values reported from other US regions. Treatment with a PGR did not result in an overall decrease in plant height. Further, PGR resulted in an increase in photosynthesis (Pn) by 8.8% but only in 2011. In cont rast for 2012, there was no effect of PGR on Pn but stomatal conductance, SPAD, and Fv/Fm were lower for PGR applied plants by 7.1%, 3.1%, and 0.5%, respectively. The harvest aid
31 paraquat led to over 6 times more leaf br owning and drop within 11 days after treatment and was more effective overall t han the tribufos harvest aid. Introduction The United States (US) government and private industries are currently dependent on foreign countries for castor oil. The US government required to keep 5 million pounds (Congress, 1991) of castor oil in stock for wartime needs (Roetheli et al. 1991). Private industries use castor oil in paints, coatings, inks, lubricants and a wide variety of other products (Ogunniyi, 2004). India, China, Brazil and Mozambique currently lead the world in ca stor production, with Paraguay, Thailand, Ethiopia, Angola, Vietnam and South Africa contributing rela tively minor amounts (FAOSTAT, 2013). In 2010, world castor production exceeded one m illion tons, with a maximum yield of 1,264 kg ha-1 (FAOSTAT, 2013). Although the US does not commercially produce castor oil, research has shown that yields of irrigat ed castor grown in Texas, on average, range from 2,242 to 3,363 kg ha-1, with some fields producing 4,035 kg ha-1 (Brigham, 1993). These results indicate that the US potentia l yield could easily exceed existing global yields. Most scholars agree that castor origi nated in the tropics of Ethiopia where it grows as a perennial up to 12 m tall and will defoliate and die when temperatures reach -4 C for four hours (Weiss, 1971). Dwarf ca stor cultivars grown in the Texas High Plains and Trans-Pecos region are 1 to 2 m in height (Brigham 1993) as compared to other varieties which range from 1.8 to 3.7 m tall (Brigham, 1970). Two dwarf cultivars, Brigham and Hale, were bred in the arid environment of Texas and registered in 1970 and 2003, respectively (Brigham, 1970; Auld et al., 2003). Hale has demonstrated the
32 potential for high yields in the US and was us ed as a parental line for the later released Brigham cultivar, which was bred for reduced ri cin seed content (Auld et al., 2003). Despite being considered as dwarf gr owth types, the cultivars Brigham and Hale still have the potential to produce ex cessive vegetation under conditions of ample rainfall. Applications of certain plant growth regulators (PGRs) may help control excessive height and internode l ength and increase harvest index of the crop overall. Plant growth regulators are exogenously applied chemicals that affect endogenously produced plant hormones, normally with the goal of reducing internode length. The plant hormone giberellic acid increases inte rnode length in plants (Taiz and Zeiger, 1998), so many PGRs that functi on as giberellic acid inhibitors are effective in reducing internode length, especially in cotton (Reddy et al., 1996; Gencsoylu, 2009) and can result in a yield benefit (Stafford, 1971). Ho wever, using giberellic acid inhibitors has shown mixed results (Oswalt, 2008; Trostl e et al., 2011). In addition to reducing internode length, giberellic acid inhibitors also have the potential to affect the photosynthetic capacity of t he crop, and ultimately yield (Zhao and Oosterhuis, 2000). Further, other related leaf level physiologi cal traits may also be impacted by PGR application including chlorophyll fluoresc ence, chlorophyll content, stomatal conductance, and transpiration. Mechanical harvest of castor will likely r equire not only limiting crop stature, but also the chemical termination of the crop to insure some level of standard maturity because of its indeterminate developmental habit. Natural crop termination occurs during freezing temperatures below -4C (Weiss, 1971) and a minimal loss of yield due to shatter can be achieved if harvested wit hin 10 days (Brigham, 1993). However, due
33 to the irregularity of a killing freeze in many regions of the southeast, a harvest aid that will desiccate and/or defoliate the crop ma y be necessary when pr oducing the crop in these areas. Some effective harvest ai ds used in southeast cotton production are tribufos (Supak and Snipes, 2000) and paraquat (Brecke et al., 2001) and would be good test candidates for crop termination in castor production. These chemicals are good preliminary test candidates because paraquat is a non-selective cell membrane disruptor and hormone regulators, like tribufos, have been shown to affect castor growth (Weiss, 2000). Defoliation percentage, leaf area index (LAI) and l eaf browning are good metrics to assess harvest aid effectivene ss in cotton (Supak and Snipes, 2000) and are likely to be useful meas urements in castor. When considering producing the crop in a southeastern region such as Florida, much of the agronomic, developmental, and physi ological assessment of the crop must be studied carefully and specifically for c onditions within this humid region. The potential for excessive height and continued growth late into the season in Florida is high and would likely require the use of pl ant growth regulators and harvest aids; therefore, determining their efficacy in the Fl orida environment is essential. Along with the effect of PGRs and harvest aids, vari etal phenotypic expression may differ between the two cultivars of interest, Brigham and Hale within this southeastern region as well. These cultivars need to be studied in this semi-tropical environment under different cultural management techniques to determine the suitability and optimal design of a castor production system in Florida. To as sess the suitability of producing castor in Florida, field trials were established at two locations within north Florida to test the use
34 of PGRs and harvest aids and quantify the effect s on phenology, physiology, maturity, LAI, rooting architecture, and yield components of both the Brigham and Hale cultivars. Materials and Methods Field Preparation and Crop Maintenance Field trials in 2011 and 2012 were conduct ed at two locations, the Plant Science Research and Education Unit (PSREU) near Citra, FL, (latit ude 29.408813N, longitude 82.173041W, altitude 21m) in a Sparr Fi ne Sand (loamy, siliceous, subactive, hyperthermic Grossarenic Paleudults); and the West Florida Research and Education Center (WFREC) near Jay, FL, (latitude 30.775999N, longitude 87.1400W, altitude 10m) in a Red Bay sandy loam (fine-loamy, kaolinitic, thermic Rhodic Kandiudults). Data was not reported for WFREC in 2012 du e to crop failure. Both sites were arranged in a completely randomized block desi gn with 3 replications and 24 plots. The plots at PSREU consisted of 6 rows within each plot with two border rows, while the plots at WFREC consisted of 4 rows within ea ch plot and one border row. Plots in both locations were 7.62 m long with 0.91 m betw een rows. Bare soil alleys, 7.32 m wide, surrounded all plots in PSREU, while at WFRE C, all but 4 of the alleys between plots were planted. Both sites were conventionall y tilled and well irrigated prior to planting. Plots were planted on 5 and 1 May 2011 and 2012, respectively, in PSREU and on 18 May 2011 in WFREC. Seed was planted at a 4 cm depth with a two-row Monosem vacuum planter using a large edible bean pl ate (Edwardsville, KS) in PSREU; and a four-row John Deere vacuum planter with a peanut plate (Moline, IL) in WFREC. All seed was provided by Dr. D.L. Auld from Texa s Tech University. Sites were thinned to an intra-row density of 6 plants m-1 (120,000 plants ha-1) at both sites in 2011. Due to
35 low yields in 2011, intra-row density was decreased to 3 plants m-1 (60,000 plants ha-1) in 2012. In 2011, PSRUE plots were broadcast fe rtilized with nitrogen (N) at 112 kg N ha-1 at 25 days after planting (D AP) and again with 33.6 kg N ha-1 at 89 DAP. In 2011, WFREC plots were broadcast fertilized once with 112 kg N ha-1 at 16 DAP. In 2012 at PSREU, fertilizer amounts remained the same, but were side dressed: 11.2 kg N ha-1 at planting, 67.2 kg N ha-1 28 DAP, and 67.2 kg N ha-1 49 DAP. Phosphorous, potassium, and other minor nutrients were added based on the recommendations for the region. For weed control, an application of 561.24g active ingredient (ai) ha-1 of trifluralin (DOW AgroSciences, Indianapolis, IN) was incorpor ated pre-plant at WFREC in 2011 and at PSREU in 2012. At both sites in both years, plots were cultivated by tractor at least twice after planting and hand weeded approximately ever y two to three weeks thereafter. Plant Growth Regulator The mode of action chosen for the PGR was a giberellic acid inhibitor with the active ingredient, mepiquat chloride. The PGR was foliarly applied at both PSREU and WFREC: Pix (BASF, Ludwigshafen, Germ any) and Stance (Bayer CropScience, Monheim am Rhein, Germany) at PSREU an d WFREC, respectively. In 2011, PGR applications were initiated when 50% of the crop was at the 6th node stage (with 2 racemes); while in 2012, the first applicat ion was applied when 50% of the crop had one flower. In 2011 at PSREU, 105.68 g ai ha-1 and 35.23g ai ha-1 of mepiquat chloride was applied 49 and 83 DAP, respectively; wh ile at WFREC, 98.78 and 37.04g ai ha-1 mepiquat chloride was applied 41 and 70 DAP, respectively. In 2012 at PSREU, 23.48g
36 ai ha-1, 58.71g ai ha-1, 58.71g ai ha-1 of mepiquat chloride was applied at 41, 51, and 62 DAP, respectively. Harvest Aid Crop defoliation and termination was accomplished with two harvest aids (HA): Def 6 ai tribufos, (Bayer CropS cience, Monheim am Rhein, Germany) and Gramoxone Extra, ai paraquat, (Zenica Agro chemicals, Deleware, US). In 2011, plots were sprayed 126 and 143 DAP in PSREU and WFREC, respectively with tribufos (rate of 1,509.72g ai ha-1) and paraquat (rate of 670.99g ai ha-1). In both years, Leaf Area Index (LAI), leaf browning, and leaf drop were a ssessed 2, 4, 7, and 11 days after HA application at the PSRUE location only. Yield, 100 Seed Weight and Oil Percentage Yield was collected by hand from the tw o inner rows at both locations and occurred twice in 2011 and weekly in 2012. The yield from the harvest(s) during the growing season included matu re brown capsules and the last harvest also included green capsules that were enlarged and showi ng signs of oil-filling. In 2011, PSRUE plots were harvested 105 and 138 DAP and WF REC plots were harvested 109 and 155 DAP. Due to high shatter losses noted befor e the first harvest in 2011, seed production over the season was followed more closel y in 2012 at PSREU, with the first yield collection at 86 DAP and additional harvests c onducted weekly thereafter until the final collection at 157 DAP. In both years, yield was determined by first drying in an oven at 60 C for a minimum of 72 hours (resulting in seeds approximately 2-3% water content) followed by completely hand threshing a r andom sub sample of approximately 20 g and applying this seed to hull weight ratio to determine final 100 seed weight and yield for each plot. In 2011, the seed oil percent age was determined by sending samples to
37 Advanced Precision Laboratories, LLC in Su mner, GA where the samples were ground and analyzed in triplicate. T he laboratory followed the AOAC Official Method 948.22 Fat (crude) in Nuts & Nut Products using a Soxtec 2050 Automated Extractor by Foss. The extraction cups were heated in a 100C ov en for more than 1 hr and then cooled in a desiccator to assure the cups are completely dry prior to extraction. The extracted oil samples were dried at 100C for 30 minutes to fully evaporate the petroleum ether from the sample and then cooled in a desiccator prio r to weighing the final sample. It was noted by the laboratory t hat the soluble starch concentrati on in the sample was minimal, thus avoiding a second extraction by water. Phenological and Physiological Measurements Season long measurements In both 2011 and 2012, LAI was measured from late May through midto late September approximately every two weeks fo r both Hale and Brigham using the nondestructive LiCor 2200 instrument (LI-CO R Environmental, Lincoln, NE). LAI measurements began 42, 21 and 35 DAP an d concluded on 119, 143 and 88 DAP in PSREU 2011, PSREU 2012, and WFREC, re spectively. One LAI measurement included regularly spaced measurements un derneath the canopy spanning the distance between rows with the sensor head held both parallel (4 readings) and perpendicular (4 readings) to the crop row with each ori entation paired with one reading above the canopy. To determine changes in total height, number of racemes, and nodes to the first raceme, ten randomly selected plants per pl ot were tagged and reassessed throughout the growing season. Total hei ght was measured to the nearest 1 cm of the tallest plant structure. The number of ra cemes included structures at initial flower formation and all
38 intermediate developmental stages through ma ture racemes. In 2011, racemes were omitted from the count if whole raceme failu re (failure to produce a harvestable capsule) was observed to better relate reproductive stru cture to yield; while in 2012, all racemes were counted regardless of raceme failure to better understand the total number of racemes possible. Nodes below the first raceme included a count of all nodes above the soil surface and below the insert ion point of the first raceme. Root architecture and growth was assess ed by regularly recording root images in the rooting zone to a dept h of almost 80 cm for both Hale and Brigham in 2011 and 2012 at PSREU. Clear plastic mini-rhizotron tubes (182.88 cm in l ength) were inserted in-row and parallel to the crop at a 45 angle with the soil surfac e. Roots were imaged along the entire length of the tube using a mini-rhizotron came ra system (Bartz, Carpinteria, CA). Images were taken 4 to 6 times throughout the growing season and analyzed using the WinRhizoTron softwar e (Regent Technology, Canada) which calculates root length and surface area for ea ch image. Analyses of root architecture (length and surface area) were separated into approximately 10 cm increments corresponding to 7 soil depth zones in 2011, and due to a deeper tube depth, 8 total depth zones in 2012. Physiological responses to PGR application To assess the impact of PGR application on leaf level physiological responses, field measurements were conduc ted on the Brigham cultivar 1 day after PGR treatment (DAT), 8 DAT, and 15 DAT. At each of these time points, field physiological measurements were taken between 0900 and 1100 EDT on the two first fully expanded leaves from two different plants within each plot. Just prior to gas exchange measurements, leaves were dark adapted fo r at least 30 minutes and the ratio of
39 variable to maximal fluorescence (Fv/Fm) for the dark adapted leaves was measured and calculated using an OS-1 fluorometer (Opt iSciences Inc., Hudson, NH). Relative chlorophyll content was then measured on t hese same leaves using a SPAD meter (Spectrum Technologies Inc.; Plainfield, IL). These same leaves were again used in gas exchange measurements while the leaves were still attached to the plants. Gas exchange was measured using a LI6400XT infra-red gas analyzer (LiCor Environmental Sciences; Lincoln, NE); leaf conditions were kept constant within the cuvette at 1800 microm oles PAR, 360 ppm CO2, and ambient temperature and atmospheric humidity. After measuring the gas exchange on a leaf, it was collected and transferred immediately to a plastic bag and stored under cool temperatures for subsequent measurement of relative water content (RWC) in the lab. At the lab, a leaf sect ion of approximately 1 cm2 was cut while avoiding the midrib for analysis (results not shown). For the remainder of the le af, the petiole was removed and leaf area was determined using the Li Cor model 3100 leaf area meter (LiCor Environmental Sciences; Lincoln, NE). The leaf was then weighed to determine fresh weight, and after soaking the leaf in distil led water under grow li ghts for approximately 3 hours, the leaf was weighed agai n to determine turgid weight. The leaf was dried at 60C for at least 72 hours and weighed again to determine dry weight. RWC was calculated using the Equation (2-1) accordi ng to Weatherly (1950). Specific Leaf Area (SLA) was calculated as the ratio of leaf area to dry weight. RWC = [fresh weight-dry weight]/[turgi d weight-dry weight] (2-1) Statistical Analysis Because management practices were di fferent between locations and years, each location/year combination (PSREU 2011, PSREU 2012, and WFREC 2011) was
40 analyzed as a separate factor and heretofore will be referred to as location/year. Multivariate and univariate repeated measur es along with ANOVA were used to analyze each of the yield, phenological and physiological characteri stics measured (JMP Pro 9 software, SAS Institute Inc., Cary, NC). Depending on the type of measurement, the following fixed factors and interactions were analyzed: location/year, plant growth regulator (PGR), cultivar (Cv.), date a fter treatment (DAT), and date after planting (DAP). A preliminary multiv ariate repeat measures MANOVA test was run and if the data passed the test of spher icity (SAS Institute, 2010) t he data were rearranged and a univariate repeated measures an alysis was conducted identifying statistically significant findings with further separation usi ng Tukeys multiple comparison test. Results Yield, 100 Seed Weight and Oil Percentage Yield, 100 seed weight, and oil percent age differed among each location/year, while yield and 100 seed weight differed among cultivars (Tabl e 2-1). All other effects and most interactions had no impact on these yield components. The highest yields were seen at PSREU 2011 and the lowest at PSREU 2012; in contrast, the highest 100 seed weights were found at WFREC 2011 and the lowest for PSREU 2011 (Table 2-2). Overall, Hale out-yielded Brigham and had a higher 100 seed weight at each location/year. By examini ng weekly yield collection in 2012 at PSREU, Hale yielded more than Brigham on a weekly basis unt il the end of the season when less than 40 kg ha-1 was collected at each harvest time (Figur e 2-1). In 2012, peak yield occurred 107 DAP and 100 DAP for Hale and Brigham, respec tively. Oil percentage was highest at WFREC 2011, averaging nearly 46% ac ross both cultivars (Table 2-2).
41 Phenological and Physiological Measurements Phenological measurements showed incr easing seasonal growth trends with some cultivar differences. Node numbers bel ow the first raceme was different among cultivars (Table 2-3) with Hale consist ently having between 1.6 and 5.2 more nodes below the first raceme than Brigham (Table 2-4). Raceme number was not affected by PGR at any location/year but was differ ent between cultivars and increased during all location/years as the season progressed (T able 2-5). Brigham produced between 3 and 8 more racemes than Hale by the end of the season, depending on location/year (Figure 2-2). LAI was also not affected by PGR but differences across dates reflected an increasing overall canopy development (Tabl e 2-6). In 2011, a par abolic LAI curve was observed both in PSREU and WFREC; whereas an increasing LAI trend through the end of the season was observed in PSREU 2012 (Figure 2-3). Peak LAI in PSREU 2011 and WFREC 2011 was observed approximat ely 76 DAP with values of 2.01 and 2.87, respectively (Figure 2-3); while at PSREU 2012, LAI reached a maximum of 2.10 at 143 DAP. Cultivars differed in LAI at PSREU 2012, when Hale averaged a higher LAI than Brigham (Table 2-6; Figure 2-3). Contrary to expectations, PGR had no si gnificant effect on plant height at PSREU in either year (Table 2-7), but actually increased height for plants in WFREC 2011 (Figure 2-4). Regardless of PGR treatm ent, plant height increased nearly linearly across the season, except for WFREC 2011 where it reached a plateau at 76 DAP (Figure 2-4). Cultivars had minimal differences for plant height with Hale significantly taller than Brigham only for WFREC 2011 (Figure 2-4).
42 Root architecture were also not affect ed by PGR, but only showed differences among dates and soil depth zones fo r both cultivars (Table 2-8). Cumulative root length (Figure 2-5) and surface area (Figure 2-6) were lower during the first date compared with all other dates. Roots we re not well developed in the top layer at soil depth zone 1 (approximately 0-10 cm below the soil surf ace) with values for both root length and surface area being lower in this zone co mpared to all other zones. However beyond this depth, the root system was fairly uniform and reached the maximum limits of the measuring tubes at a depth of 73.4 cm in 2011 and 83.9 cm in 2012 (Figure 2-5; Figure 2-6). Physiological responses to PGR application The applications of PGR had a limited e ffect on most of the physiological processes measured in this study but did increase Pn in 2011 (Table 2-9; Table 2-10) with rates at 24.71 and 22.72 mol CO2 m-2 s-1 for PGR treated and non-treated plants, respectively (Table 2-10). However, a ll other measurements (conductance, Ci, transpiration, SPAD, Fv/Fm, RWC, leaf area, and SLA) were not affected by PGR in this year (Table 2-9; Table 2-10). Although DA T had an effect on Pn and SPAD, there were no obvious increasing or dec reasing trends evident (Table 2-10). These effects on photosynthesis were not present in 2012 but PGR lowered conductance, SPAD, and Fv/Fm (Table 2-9; Table 2-10). Conduc tance for PGR treated and non-treated plants was 0.98 and 1.05 mol H2O m-2 s-1, respectively; while SPAD for PGR treated and nontreated plants was 39.84 and 41.06, respective ly (Table 2-10). In the case of conductance readings had not obvious trend with DAT, but with SPAD, readings increased with increasing DAT. Fv/Fm fo r PGR treated and nontreated plants was 0.817 and 0.821, respectively with no obvious trend with DAT.
43 Effectiveness of Harvest Aid treatment In both years, the type of harvest aid and days after treatm ent did affect LAI, leaf drop and leaf browning, but prior PGR application and cult ivar did not influence the response to HA treatment (Table 2-11). Pa raquat was overall more effective than tribufos in desiccating and defoliating the crop during both years as indicated by greater decreases in LAI and substantially higher l eaf browning and leaf drop percentages. By 7 DAT paraquat decreased LAI 1.3 and 1.7 time s more than tribufos when compared to the pre-treatment value duri ng 2011 and 2012, respectively (Figure 2-7). The slight increase in LAI at 11 DAT is likely due to leaf regrowth that was visually noted in the field. Regardless of HA product, leaf brow ning was observed at 2 DAT, whereas leaf drop lagged and was observed starti ng at 4 DAT. As with LAI, by the end of the season paraquat had substantially increa sed levels of visually ra ted leaf browning and drop over tribufos with 26.7 and 6.64 times more leaf browning and 117.1 and 9.3 times more leaf drop in 2011 and 2012, res pectively (Figure 2-7).
44 Table 2-1 ANOVA of Yield, 100 Seed We ight and Oil Percentage. F values for treatment effects on oil percent age in PSREU and WFREC in 2011 Yield 100 Seed Weight Oil Percentage Effect df F Value df F Value df F Value Location/year 2 15.0916* *2 21.9179**1 77.4129** Cv. 1 6.0342* 1 18.0244**1 1.1936 PGR 1 1.9776 1 0. 0264 1 2.4749 Harvest Aid 1 0.4502 1 0.4918 1 0.1553 Location/year *Cv. 2 2. 4633 2 0.3477 1 0.2139 Location/year *PGR 2 1.0859 2 1.3067 1 2.3851 Location/year *HA 2 0. 2132 2 1.3687 1 1.7273 Cv*PGR 1 0.1097 1 0.1806 1 0.2551 Cv.*HA 1 0.4802 1 0.1383 1 4.6386* PGR *Harvest Aid 1 0. 0835 1 0.0003 1 0.5010 Location/year *Cv. *PGR 2 0.3824 2 1.2367 1 5.7043* Location/year *Cv.*HA 2 0.0272 2 1.4347 1 0.4938 Cv.*PGR *HA 1 0.9485 1 0.4447 1 0.0144 Location/year *PGR *HA 2 0.1749 2 0.0866 1 0.3666 Location/year *PGR*HA*Cv. 2 0.2616 2 0.3349 1 1.8719 ** Indicates P < 0.01 Indicates P < 0.05 Table 2-2 Mean values for Yield, 100 Seed Weight and Percent of Oil Location Year Cv. PGR Yield (kg ha-1) 100 Seed Weight (g) Percent of Oil PSREU 2011 Brigham Yes 1311.24ab 17.79c 43.43bc PSREU 2011 Brigham No 1403.29a 18.03c 43.56bc PSREU 2011 Hale Yes 1238.31abc 19.25bc 42.71c PSREU 2011 Hale No 1382.78a 19.79bc 42.90bc PSREU 2012 Brigham Yes 645.61c 21.27bc n/a PSREU 2012 Brigham No 725.55bc 21.55bc n/a PSREU 2012 Hale Yes 1094.22abc 22.36a n/a PSREU 2012 Hale No 942.26abc 23.49a n/a WFREC 2011 Brigham Yes 746.1babc 19.29ab 45.63a WFREC 2011 Brigham No 960.26abc 19.52ab 45.64a WFREC 2011 Hale Yes 1236.30abc 22.72a 45.66ba WFREC 2011 Hale No 942.26abc 20.71a 46.20a Columns not connected by same le tter are significantly different
45 Table 2-3 ANOVA of Nodes to First Raceme F values for treatment effects on LAI in PSREU and WFREC in 2011 and 2012 PSREU 2011 PSREU 2012 WFREC 2011 Effect df F Value df F Value df F Value Cv. 1 151.3588* 1 69.8386* 1 108.0846* Indicates P < 0.01 Table 2-4. Mean values for nodes below first raceme Location Year Cv. Nodes PSREU 2011 Brigham 6.9 PSREU 2011 Hale 12.1 PSREU 2012 Brigham 6.6 PSREU 2012 Hale 8.2 WFREC 2011 Brigham 7.3 WFREC 2011 Hale 11.6 Locations and years were analyzed separately Table 2-5 ANOVA of Racemes. F val ues for treatment e ffects on number of racemes in PSREU and WFREC in 2011 and 2012 PSREU 2011 PSREU 2012 WFREC 2011 Effect df F Value df F Value df F Value PGR 1 0.3286 1 1.7557 1 3.5008 Cv. 1 45.4482* 1 60.1636* 1 47.0187* Date 5 390.6655* 5 243.9103* 4 78.8326* PGR Date 5 0.0961 5 1.6059 4 1.6617 PGR Date Cv. 5 0.5815 5 0.0396 4 3.5094* Cv. Date 5 9.6645* 5 25.6111* 4 9.2719* Cv. PGR 1 1.1558 1 0.0463 1 1.6472 Indicates P < 0.01 Table 2-6 ANOVA of LAI. F values fo r treatment effects on LAI in PSREU and WFREC in 2011 and 2012 PSREU 2011 PSREU 2012 WFREC 2011 Effect df F Value df F Value df F Value PGR 1 0.4652 1 0.7301 1 0.6905 Cv. 1 0.0185 1 20.8099* 1 0.3011 Date 8 24.3438* 5 51.4606* 2 77.5382* PGR Cv. 1 0.0435 1 2.5737 1 1.1615 PGR Date 8 0.6518 5 0.2542 2 0.6612 PGR Cv. Date 8 0. 3645 5 0.5457 2 0.9340 Cv. Date 8 0.7824 5 3.3368* 2 0.9265 Indicates P < 0.01
46 Table 2-7 ANOVA of Height. F values fo r treatment effects on height in PSREU and WFREC in 2011 and 2012 PSREU 2011 PSREU 2012 WFREC 2011 Effect df F Value df F Value df F Value PGR 1 0.4427 1 0.0001 1 225.8337* Cv. 1 0.4721 1 0.0450 1 14.6739** Date 5 263.8146**7 256.0689**4 235.1695** PGR Cv. 1 0.5711 1 0.4382 1 0.0957 PGR Date 5 0.4144 7 0.0583 4 0.7212 PGR Cv. Date 5 0. 7135 7 0.0513 4 0.0716 Cv. Date 5 2.9457* 7 0.4183 4 6.5616** ** Indicates P < 0.01 Indicates P < 0.05 Table 2-8 ANOVA of Root Architecture. F values for treatment effects on Surface Area and Length in PSREU in 2011 and 2012 SA 2011 SA 2012 Length 2011 Length 2012 Effect df F Value df F Value df F Value df F Value PGR 1 2.8661 1 1.4789 1 1.2196 1 1.5845 Cv. 1 0.2254 1 0.0382 1 0.0001 1 0.6156 Date 3 7.7107* 4 12.2915*3 11.6541* 4 16.2283* PGR Cv. 1 1.0677 1 0. 8071 1 1.6246 1 0.8512 PGR Date 3 0.4252 4 2. 0701 3 0.5580 4 2.3277 PGR Cv. Date 3 0.2811 4 1.4382 3 0.1458 4 1.8707 Cv. Date 3 0.7033 4 2. 2968 3 0.4387 4 3.1313** Zone 6 17.2248*7 10.5288*6 15.5662* 7 13.2032* PGR Zone 6 5.5721* 7 4.3364* 6 4.0056* 7 5.3415* Cv. Zone 6 1.5387 7 8.2720* 6 1.0317 7 5.8864* Date Zone 18 0.7852 28 1. 2724 18 1.1655 28 1.8535* PGR Cv. Zone 18 1.0979 7 9.7399* 18 1.1955 7 8.2005* PGR Date Zone 6 0.2410 28 0.7422 6 0.1561 28 0.8000 PGR Cv. Date Zone 18 0.2678 28 0.6497 18 0.2183 28 0.6432 Cv. Date Zone 18 0.1611 28 0.7875 18 0.2259 28 0.7402 Indicates P < 0.01 ** Indicates P < 0.05
47 Table 2-9 ANOVA of leaf leve l physiological traits. F val ues for treatment effects in PSREU in 2011 and 2012. Data was analyzed within each year separately. Pn Conductance Ci Transpiration SPAD Fv/Fm RWC Leaf Area SLA Effect Df F Value F Value F ValueF Value F Value F Value F Value F Value F Value 2011 PGR 1 352.4450* 0.41312.89250.273017.7278 0.11350.99530.15090.0176 DAT 2 4.6487* 0.85741.39861.73625. 1536* 0.13913.9693*3.00001.7000 PGR DAT 2 0.0177 0.68310.07010. 21980.8938 1.24502.01311.24670.9400 2012 PGR 1 3.4873 48.7054*0.84022.036298. 0382* 71.7037*3.32570.27320.1823 DAT 2 0.6592 0.26051.378311.5479**5.5941* 9.2492**41.3429**0.785115.4288** PGR DAT 2 0.9820 1.81560.99551. 56850.2832 0.11860.11500.04670.8038 ** Indicates P < 0.01 Indicates P < 0.05
48 Table 2-10 Mean values for Photosynthetic E ffects on Brigham in PSREU in 2011 and 2012 Year DAT PGR Pn (mol CO2 m-2 s-1) Conductance (mol H20 m-2 s-1) Ci ( mol CO2 mol air-1) Transpiration (mol H20 m-2 s-1) SPAD RWCFv/Fm Leaf Area (cm2) SLA (cm2/g) 2011 1 No 24.67 1.53 278.25 14. 11 39.19 0.92 0.82 180.28 229 2011 8 No 20.91 1.24 285.06 12. 41 35.62 0.91 0.81 217.13 222 2011 15 No 22.59 2.15 284.42 15. 44 41.18 0.91 0.83 159.03 237 2011 1 Yes 26.64 1.51 274.17 13. 48 41.63 0.92 0.82 162.35 203 2011 8 Yes 22.67 1.33 280.37 12. 88 40.26 0.87 0.82 197.61 215 2011 15 Yes 24.50 1.42 277.86 14. 31 42.80 0.91 0.79 186.02 277 2012 1 No 26.19 1.04 262.12 11.68 39. 23 -0.83 174.51 227 2012 8 No 27.28 1.14 265.34 10.61 40. 58 0.92 0.81 163.45 198 2012 15 No 26.38 0.95 260.05 9.18 43. 36 0.89 0.83 173.87 183 2012 1 Yes 25.12 0.93 258.88 11.10 38. 38 -0.82 169.93 221 2012 8 Yes 25.36 0.95 263.51 9.71 39. 92 0.90 0.8 157.45 188 2012 15 Yes 27.48 1.07 263.31 9.68 41. 24 0.86 0.82 174.78 190
49 Table 2-11 ANOVA of Post Harvest Aid Appl ication: LAI, Leaf Drop and Leaf Brown. F values for treatment effects on height in PSREU in 2011 and 2012 LAI Leaf Drop Leaf Brown Effect df F Value df F Value df F Value 2011 PGR 1 0.905812.46941 0.1176 Cv. 1 0.0008 10.00891 0.7517 DAT 3 27.1423**328.9952**3 92.3673** HA 1 79.5182**112870.75**1 531.5715** PGR HA 1 1.618611.00001 0.0294 Cv. DAT 3 0.431530.80243 1.8459 PGR HA Cv. 1 2.621410.00891 1.1230 PGR Cv. 1 3.797910.00891 0.5940 PGR DAT 3 0.709630.36873 0.7300 HA Cv. 1 0.779710.00891 1.3364 HA DAT 3 0.9477318.6723**3 89.7914** PGR DAT 3 0.622232.53733 0.4380 HA Cv. DAT 3 1.540030.88923 2.0649 2012 PGR 1 1.179110.89291 0.0063 Cv. 1 2.138511.24621 2.8802 DAT 3 44.8109**3757.0751**3 71.0513** HA 1 36.0865**13217.687**1 16660.32** PGR HA 1 13.5492*11.75001 0.0570 Cv. DAT 3 2.528531.21043 2.9487* PGR HA Cv. 1 0.006810.75381 0.2258 PGR Cv. 1 0.349110.13851 0.7788 PGR DAT 3 0.761830.93993 3.7692* HA Cv. 1 1.646010.38461 0.5576 HA DAT 3 4.52993516.2998*3 32.2821** PGR DAT 3 0.556630.07443 0.6923 HA Cv. DAT 3 0.812530.93993 2.3333 Indicates P < 0.05 ** Indicates P < 0.01
50 Figure 2-1 PSREU 2012 Week ly yield collection
51 Figure 2-2 Total Number of Racemes. PSREU 2011(a), PSREU 2012 (b), and WFREC (c) c b a
52 Figure 2-3 Leaf Area Index. PSREU 2011 (a), PSREU 2012 (b), and WFREC (c) c b a
53 Figure 2-4 Plant height. PSREU 2011( a), PSREU 2012 (b), and WFREC (c) c b a
54 Figure 2-5 Root Length by soil depth z one (in 10 cm increments) for 2011 and 2012 reported by DAP. 50 DAP in 2011(a), 70 DAP in 2011 (b), 92 DAP in 2011 (c), 106 DAP in 2011 (d), 38 DAP in 2012 (e), 58 DAP in 2012 (f), 73 DAP in 2012 (g), 93 DAP in 2012 (h), 142 DAP in 2012 (i), a b c d e f g h i
55 Figure 2-6 Root surface area by soil dept h zone (in 10 cm increments) for 2011 and 2012 reported by DAP. 50 DAP in 2011(a) 70 DAP in 2011 (b), 92 DAP in 2011 (c), 106 DAP in 2011 (d), 38 DAP in 2012 (e), 58 DAP in 2012 (f), 73 DAP in 2012 (g), 93 DAP in 2012 (h), 142 DAP in 2012 (i), a b c d e f g h i
56 Figure 2-7 Harvest Aid effects in PSREU 2011 and PRSEU 2012. Percent Brown (a), Percent Leaf Drop (b), and LAI (c) b a c c b a
57 Discussion By assessing the response of two cast or cultivars to agronomic management techniques, the main goal of this proj ect was to evaluate different management techniques that could be employed in a cast or cropping system for the southeastern US region. The maximum yields achieved in any treatment in the curr ent study were 1,403 kg ha-1 with most treatments av eraging below 1,000 kg ha-1. These yields are higher than previous results from Florida and co mparable with current yields from other countries (FAOSTAT, 2013), but are low wh en compared to the optimum production levels achievable domestically in Te xas in the range of 2,242 to 3,363 kg ha-1, with some fields producing 4,035 kg ha-1 (Brigham, 1993). Severa l seed factors may have contributed to the yield leve ls in Florida including rela tively low 100 seed weights and low oil percentages. In this study, the 100 seed weight ranged from 17.79 to 23.49 g which are lower in comparison to Texas grow n seed (27.60 to 33.22 g) and at the lower range of seed produced globally (10.1 to 73. 3 g with an average of 28.3g; Wang et. al, 2010). The Florida seed also had a lower per centage of oil by weight (42.7-46.2%) when compared to the average ( 48.2%) of the USDA castor germplasm (Wang et al., 2010). One contributing environm ental factor to the low yi elds was the presence of mold on the racemes. Gray mold was previ ously reported as one of the main limiting factors for successful castor cultivation in the southeast (Domingo, 1953; Weiss, 1971; Godfrey, 1919) and the presence of an unident ified mold was detected in the current study, with the greatest pr oblems noted at WFREC 2011 and PSREU 2012. Whole raceme failure and individual capsule fa ilurepresumably due to moldwas observed in both locations and likely reduced yield. In fact, over 70% of the total harvest in WFREC 2011 was gathered at the first harve st and subsequent periods of heavy rain
58 promoted mold growth and ultimate ly raceme failure. It is possible that antifungal spray plans may help alleviate this yield-reducing pr oblem in the future. The combination of early maturing habits, raceme size, and pr opensity to shatter also likely played an integral role in producing low yields in this study. Flowers were first observed around 35 DAP in Florida, which is much earlier than t he average flowering times of 47 DAP in the US (Weiss, 2000). The plants likely did not have as much vegetative growth as other castor grown in the US when flowering star ted and it is possible that this lack of photosynthetic capacity resulted in less photoa ssimilate for the gr owing racemes. The early flowering could explain why the prim ary and secondary racemes were typically smaller than those produced in Texas (Weiss, 2000) or Israeli cultivars that were examined in grower fields in south Florida (personal observation). In 2011, excessive shatter was also noted at the first harve st at 105 DAP and 109 DAP in PSREU and WFREC, respectively. Quantification and characterization of s easonal growth habitsheight, number of nodes below the first raceme, LAI, and rooting architectureof castor grown in Florida are necessary to evaluate any cropping system for this area. These seasonal growth habits are important because data on height and nodes below the first raceme will affect mechanical harvesting; LAI will characterize canopy growth and development; and rooting architecture will affect cultivati on and propensity for deep mining of nutrients in the soil. Overall canopy growth in this study showed a typical increasing pattern throughout the season, with LAI showing a par abolic trend peaking at 76 to 77 DAP for all locations/years except for PSREU 2012, which showed an increasing trend until the end of the season. Maximum LAI was not ed as 2.01, 2.87, and 2.10 for PSREU 2011,
59 PSREU 2012, and WFREC 2011, respective ly. These peak LAI measurements are somewhat low in comparison to other cr ops, including sorghum (7.8) (Muchow and Davis, 1988), soybean (3-6) (Shibles and W eber, 1965) and cotton (5-7) (Ashley et al., 1965). In previous research, castor leaf area has been correlated with leaf length (Wendt, 1967), and LAI has been computed (Vijaya Kumar, et al., 1996), but overall LAI has not been reported. Given that, it is not possible to compare these maximum LAI values with previous research to determine whether they are repres entative. In this research, root length and surface area measurements effectively demonstrated numerical differences in plant ing density, root senescence, differences in root zone growth, and root growth rate. The lower density planting in 2012 resulted in lower overall cumulative root growth, but growth patterns were similar with a peak around 70 DAP in both years. Measurem ents in 2012 were conducted longer than 2011 and, as a result, root senescence was observed at 142 D AP. Interestingly, both the root length and surface area in the shallowe st depth, zone 1 (0-10cm), were consistently lower than all other depths in both years. Farm m anagers have been advised to be mindful of the shallow spreading root system of castor plants when cultivating (Weiss, 2000), but unless the cultivation tool reaches well pas t 10 cm, significant root damage may not occur for castor grown in Florida. Castor roots grew downward at the rate of 14 mm day-1 by 50 DAP in 2011 and 20 mm day-1 by 21 DAP in 2012. These roots extended past the viewing area (80 cm) by 70 DAP and it is likely that t he roots continued deeper in the soil, thus allowing for a greater distribution within the soil profile and a potential for mining for minerals and water. Rooting habit has been noted in previous literature, but
60 data of this type have never been reported for castor and r epresent import ant botanical information that could be applied to various US production regions. One of the most important and perhaps surprising results of the current study is the lack of effect of PGR on t he height in either castor cu ltivar. Because plant height was not affected in 2011, PGR app lication was initiated earlier in an effort to optimize its effect in 2012. The lower concentrat ion, but higher frequency rates applied in 2012 were more similar to the recommendations for cotton crop management (Supak and Snipes, 2000). However, even with a diffe rent application scheme, there were no impacts on plant height. PGR application may not be required for these cultivars as the tallest average height of 115.2 cm noted in t he current study was wit hin the upper limit of the suggested range (30-125 cm) for mechanical cultivation (Auld et al., 2003) and is similar to the dwarf cultivars (100-200cm) grown in the Texas High Plains and TransPecos region (Brigham 1993). Al though PGRs did not affect height, they did affect photosynthetic capacity differently in 2011 ve rsus 2012. In 2011, the PGR-applied plots had significantly higher photosynthetic rates, while this effect was absent in 2012 which recorded lower values for conductance, SPAD, and Fv/Fm. Giberellic acid inhibitors have been shown to both decrease (Reddy et al., 1996) and increase (Zhao and Oosterhuis, 2000) the photosynthet ic rate of cotton and the resu lts from this study show similar gas exchange results for castor. Ov erall gas exchange rates measured in this study match previously measured photo synthesis, stomatal conductance, and transpiration for castor (Zhao and Oosterhuis 2000; Pinheiro et al., 2008; Dai et al., 1992).
61 Due to the irregularity of a killing freeze in Florida, the use of a harvest aid is likely to be a necessary cropping system componen t, and the results of this study reveal that paraquat is a much more effective har vest aid than tribufos. The goal of the harvest aid is to decrease the amount of v egetative material such that a mechanical harvester can more efficiently harvest and s eparate seed from vegetative material. Leaf browning will increase the harvest efficiency as it is an indicator of leaf desiccation, but leaf drop will increase harvest efficiency even more as no vegetative material will enter the combine. Visual observations of leaf browning and leaf drop were confirmed by a significant decrease in LAI pos t HA treatment. Paraquat was remarkably more effective than tribufos as a harvest aid averaging 1.5 times more LAI decreas e, almost 15 times more leaf browning, and over 63 times more leaf defoliation after 11 DAT. The effects of paraquat as a harvest aid are comparable with past studies in cotton, but tribufos defoliation percentages are much lower. In one study the least effective harvest aid in cotton defoliated 51.2% of the leaves afte r 7 DAT (Anonymous, 1999) as compared to the leaf defoliation findings in this st udy with paraquat and tribuf os average of 79.4% and 3.1% after 7 DAT, respectively. Paraquat did not kill all the plants at the 2.1 L ha-1 rate, but the fact that it kill ed some may prevent it from be ing a harvest aid if rattooning the crop becomes a viable option. It is interesting that the hormone-related leaf abscission inducing mechanism of tribufos was not very effective as a harvest aid given that previous literature stat es castor is severely damaged by hormone type herbicides (Weiss, 2000). Due to the presence of regr owth at 11 DAT, the recommended harvest date may be 10 days or less to take full effe ct of the harvest aid, avoid shatter, and avoid regrowth that would r educe the harvest efficiency.
62 In conclusion, yield needs to be increased if castor production in Florida is to be competitive within a po tential US market. Mepiquat chloride, as a plant growth regulator, did not affect plant height and had conflicting effects on the photosynthetic capacity of the crop. Tribuf os did not effectively terminat e the crop in this cropping system, but Gramxone worked well, as long as the crop is not managed in a rattooning system. Future research is needed to further evaluate the potential to grow castor in Florida, especially by incorporati ng fungicides and other disease management strategies. This project focused on a cropping system with a si ngle harvest, but the results of this study combined with potential to grow castor in a rattooning system (data not shown) may suggest rattooning is a more economically sustainable cropping system for castor in Florida.
63 CHAPTER 3 ASSESSING SAP FLOW RATES AND DETERMINING KC CURVES FOR CASTOR PRODUCTION IN FLORIDA Chapter Abstract Innovative location and crop-specif ic production systems are capable of conserving agricultural water use, and one e ffective method is the quantification of water-use and development of crop coefficien ts particular to a production region. To develop irrigation recommendations suited for ca stor production in north central Florida, research was conducted at the Plant Science Re search and Education Unit in Citra, FL. Season-long field measurements of sap flow were collected for the castor ( Ricinus communis L.) cultivar Brigham in 2011 and 2012 and soil evaporation rates were quantified in 2012. Sap flow was analyze d when the plots had reached complete canopy cover, were fully irrigated, and when daily solar radiation levels were at or above a historical radiation average to ensure opt imum growing conditions. Soil evaporation rates were significantly lower than plant tr anspiration and as a result the season long transpiration was the main factor for the calculation of crop evapotranspiration (ETc) calculated on an area basis. ETc was evaluated against a calculated reference evapotranspiration (ETo) from site specific meterological readings to calculate daily Kc values. 10-day Kc averages were compared to published Kc values from the Food and Agriculture Organization of the United Nations (FAO) for castor. The timeframes were roughly aligned and the mid-season Kc values were similar, but the late season Kc values for castor in Florida were higher as compared to the mid-season. The increase in water use throughout the season could be ex plained by a lack of physiological cut out and continued irrigation applic ation. These results provide appropriate Kc values for
64 north-central Florida and will ai d growers in irrigation deci sions when producing castor in this region. Introduction Agriculture uses approximately 80 perc ent of the nations consumptive water resources (USDA ERS, 2012). Innovative an d location and crop specific production systems are needed to conserve water use by agric ulture. Castor requi res 20.6 to 24.7 cm ha-1 of water (Brigham, 1993) to obtai n optimal growth and production and supplemental irrigation can increase yields by 32 to 49 percent (Laureti et al., 1995; Weiss, 2000). Castor can be grown in many regions without supplemental irrigation, including the semi-tropical climate of Florida. However, the combination of sandy soils and periodic drought within th is region would likely re quire a cropping system with irrigation to achieve the highest yields. To optimize the efficiency of irrigation application any cropping syst em, it is necessary to quantify seasonal crop water-use for crops grown in that particular region. Tota l water use in any agricultural field can be quantified as the additive factors of ev aporation from the soil surface (E) and transpiration of the crop (Tc), which are collectively called crop evapotranspiration (ETc) (see Equation 3-1) (Allen et al., 1998). Water used by the crop can be directly measured with weighing lysimeters or direct measures of evaporat ion and transpiration (Sakuratani, 1981; Ham et al., 1990). ETc = E + Tc (3-1) Alternatively, ETc can be calculated based on cr op and cropping system specific characteristics including al bedo, crop height, aerodynamic properties, irrigation, and harvest moisture content (Allen and Pruitt, 1991) which together constitute the crop
65 coefficient (Kc). This Kc value is then multiplied to a modeled reference rate of evapotranspiration (ETo) derived from meteorological data. ETc then equals the product of a reference ET (ETo) and the Kc value for different crop gr owth stages (see Equation 3-2) (Allen et al., 1998). ETc = ETo x Kc (3-2) Calculations of ETo vary between location, season and the reference crop chosen. Currently, the standard ETo is based on a hypothetical gra ss crop in local climatological conditions and is calculated using the P enman-Monteith model (Monteith, 1965). Kc values indicate the relative difference in water use between the crop and the reference; for example, a Kc value above 1 indicates that the crop is using more water than the reference crop and Kc values below 1 indicate that the crop is using less water. Growers in Florida can collect free ETo values online, relevant to their particular area, from the Florida Automat ed Weather Network (FAWN) which collects data from 37 weather stations across the state (FAWN, 2012). With appropriate Kc values for castor, growers can easily make the calculation of ETc to determine the crop water requirement and use it to apply supplemental irrigation abov e rainfall to meet crop water demand. The Food and Agricultural Organization (FAO) has published Kc values for various crops including castor (Doorenbos and Kassam, 1979; Doorenbos and Pruitt, 1977), and further sources have updated the Kc calculation methods (Snyer and Pruitt, 1989; Wright, 1981). Typically, Kc values are assigned to three developmental timeframes: initial, mid, and late for many cr ops, including castor (Allen et al., 1998). The main factor determining early season Kc values are soil type, frequency and intensity of wetting and duration of soil surface wetness. Mid-season Kc values are
66 based on crop specifics (albedo, crop height, and aerodynamic properties) and environment (relative humidity ab ove 45% and windspeed at 2 m s-1). The late Kc is indicated by yellowing of leaves and a natural senscence where the Kc is more reflective of irrigation practices and soil evaporation (A llen et al., 1998). De viation from these Kc values according to environment (hum idity) and crop management (wetting frequency and intensity, water percentage in harvested crop) occur with arid /windy conditions increasing Kc values and humid/stagnant conditions decreasing the Kc values (Allen et al., 1998). However, the FAO recommends that additional studies should be conducted in specific environments to determine more accurate Kc values and timeframes for each specific location (Allen et al., 1998). Therefore developing Kc values specific for Florida environmental conditions is essential for optim izing the efficiency of irrigation application in the region. Determining ETc values for calculation of regional specific Kc values has primarily been determined by weighing lysimeters in t he field or greenhouse. An alternative method that can be employed in the field uses direct measurements of transpiration (Tc) and soil evaporation separately (Sakurat ani, 1981; Ham et al., 1990). Logged measurements of transpiration are possible through the use of sap flow technology (Sakuratani and Abe, 1984; Ham et al., 1990) and measurements of soil evaporation can be carried out in the field using microlysimeters (Boast and Robertson, 1982). Sap flow collected throughout the season is equival ent to plant transpira tion (Dynamax Inc., 2005); and sap flow measurements have been s hown to be equivalent to within 10% of the crop water use measured in weighing lysi meters (Baker and Bavel, 1987; Smith and Allen, 1996; Hattan et al., 1990). Soil evaporation meas urements using the micro-
67 lysimeter method are reliable when a ssessing water loss over 1-2 days with measurements consistent ly within a 0.5 mm range (Boast and Robertson, 1982). To address the need of providing castor Kc values appropriate to the Florida environment, this study measured the transpi ration of the castor crop at full canopy coverage in the field under optimal conditions using sap flow collars attached to the stem below all branches of the plant. These measurements of transpiration were combined with direct measurement of soil evaporation in the field using a mini-lysimeter (Boast and Robertson, 1982). The resulting ETc values were compared on a 10 day time step to ETo values as measured by a FAWN weather station located and the research site and Kc values were calculat ed using Equation 3-3: Kc = ETc/ETo (3-3) Materials and Methods Field Preparation and Crop Maintenance Field trials in 2011 and 2012 were conduct ed at the Plant Science Research and Education Unit (PSREU) near Citra, FL, (l atitude 29.40N, longitu de 82.17W, altitude 21m) in a Sparr Fine Sand (loamy, siliceous subactive, hyperthermic Grossarenic Paleudults). The plots at PSREU consist ed of 6 rows 7.62 m long with 0.91 m between rows. Bare soil alleys, 7.32 m wide, surr ounded all plots. Plots were conventionally tilled and well irrigated prior to planting and received supplemental irrigation to ensure plants received adequate moisture. Plots we re planted on 5 May 2011 and 1 May 2012. The castor cultivar Brigham was planted at a 4 cm depth with a two-row Monosem vacuum planter using a large edible bean pl ate (Edwardsville, KS). All seed was provided by Dr. D. Auld from Texas Tech Un iversity. Sites were thinned to an intra-row density of 6 plants m-1 in 2011; however, due to low yields and perceived excessive
68 plant-to-plant competition indicated by some short statured plants and random plant death in 2011, intra-row density was dec reased to the rate of 3 plants m-1 in 2012. In 2011, plots were broadcast fertiliz ed with nitrogen (N) at 112 kg N ha-1 at 25 days after planting (DAP) and again with 33.6 kg N ha-1 at 89 DAP. In 2012, fertilizer amounts remained the same, but were side dressed: 11.2 kg N ha-1 at planting, 67.2 kg N ha-1 28 DAP, and 67.2 kg N ha-1 49 DAP, with phosporous (P), potassium (K), and other minor nutrients added at planting based on the recommendations for the region. Weed management was accomplished by incorporating 561.24g ai ha-1 trifluralin (DOW AgroSciences, Indianapolis, IN) prior to planti ng, followed by inter-row cultivation and hand weeding as needed. Soil Evaporation Measurements and Data Analysis Soil evaporation amount and rates were determined in the field using a minilysimeter in 2012 (Boast and Robertson, 1982) Soil evaporation was determined at 50 days after planting (DAP) and at 69 DAP, a dat e when the soil was dry as characterized by a lack of rain/irrigation event of more t han 48 hours prior. Six mini-lysimeters were used, 3 in row and 3 between row to determine the average evaporation rate per plot. Using a section of PVC pipe( dimensions: depth= 70mm, di ameter=100mm), a soil core was taken, immediately weighed and retu rned to the field and placed within the excavated soil core. After 1 to 2 days, the core was weighed again and the difference in weight was equal to the water lost via evaporation (Boast and Robertson, 1982). Sap Flow and Meteorological M easurements and Data Analysis In 2011, SGEX-13 sap flow collars (Dynamax Inc., Houston, TX) were installed on eight Brigham plants after the stems were approximately 13 cm in diameter. The collars work according to the heat bal ance method (Baker and Bavel, 1987) and are
69 indexed to the stem diameter (Smith and Allen, 1996) to determine sap flow. A heating strip (source of the heat pulse) is lo cated between two thermocouples and the difference in temperature between the ther mocouples can be used to calculate Tc. Plants that exhibited a growth pattern (hei ght, stem diameter and number of racemes) similar to most other plants in the plot were identified and selected for installation of the collars. The same eight SGEX-13 collars re mained on the plant throughout the growing season. In 2012, plants were similarly sele cted, but the stem diam eter was larger than in 2011, with four plants requi ring the SGB-16 and four requiri ng the SGB-25 collars at installation. SGB-16 collars were subs equently changed to SGB-25 collars to accommodate increases in st em diameters. In each year, collars and data were regularly checked and collars were moved to alternative plants as needed. Data from each year were logged every 15 minutes thr oughout the installation period. Collars were installed 51 DAP and 45 DAP and re moved 118 DAP and 143 DAP in 2011 and 2012, respectively. Data were analyzed similarly in both y ears. When the collars were working properly missing data points result ing from a lost electrical signal were indicated by the ouput of the datalogger and were eliminated from the analysis. To increase accuracy, data points extending one hour before and afte r these missing values were excluded from consideration to allow the stem/colla r time to thermally equilibrate (representing approximately 1.7% and 4.5% of the data points in 2011 and 2012, respectively). The flow rates reported by the instrument (g hr -1) were converted to L minute -1 based on the density of water (1 g mL-1) as over 99% of sap flow is water (Dynamax Inc., 2005) and averaged across all collars at 15 minute in tervals. These flow rates were also
70 summed on a daily basis to determine total sap flow in a 24 hour period measured in L day-1. Finally, total sap flow on a per area basis was calculated by multiplying flow rates of individual plants by plant density with re sults expressed on a per land area basis (L day-1 ha-1). In calculating Kc values for the region, the goal was to determine the typical water-use of the crop under conditions t hat reflected at or above historical meteorological conditions. Because solar radi ation is a primary driv er of transpiration, historical radiation levels were used to filter sap flow values that occurred under atypical environmental conditions duri ng 2011 and 2012. Historical in-season solar radiation data from 2005 to 2010 was collected from the FAWN network (FAWN, 2012) and averaged at 10 day increments to determine historical baseli ne typical radiation levels for those time periods. In both 2011 and 20 12, daily in-season solar radiation levels that were below the historic al baseline were indicative of a sub-optimal growing condition and sap flow readings for those dates were not included in the development of the Kc values; this resulted in exclusion of 42.6% and 40.6% of sap flow values recorded in 2011 and 2012, respectively. For illustrative purposes Figure 3-1 graphically shows the days that were exclud ed during which daily radiation levels fell below the historical radiation level. Afte r removal of these points, both linear and nonlinear regression analysis were used to analyze the shape of the curve of sap flow over time (JMP Pro 9 software, SAS Institute In c., Cary, NC) and significance of these regressions were determined at the p < 0.05 level. Kc values are reported on a 10 day basis by averaging daily Kc calculations for greater reso lution than the typical midor late-season single values reported by FAO.
71 Results and Discussion The average soil evaporation rates were 38 L ha-1 day-1 and the average transpiration rates were 57,199 L ha-1 day-1 and 56,560 L ha-1 day-1, for 2011 and 2012, respectively. This soil evaporation rate was only 0.07% of the lowest average daily transpiration rate and contri buted only 0.001 to the Kc value; therefore, ETc values were set equal to Tc values. The average measureable daily sap flow occurred between 0800 and 2000 EDT for 2011 and 2012 (Figure 3-2) with peaks at 1415 and 1300 EDT in 2011 and 2012, respectively. Sap flow pa tterns mirrored daily solar radiation levels (except for a short lag time for sap flow in the early morning hours). Radiation levels increased at 0600 and declined to near zero around 1900 EDT and peaked at 628 and 741 w m-2 at 1145 and 1215 EDT in 2011 and 2012, respectively (Figure 3-3). The values in peak sap flow rates per plant in 2011 were much lower than in 2012 with a seasonal average maximum of almost 150 g hr-1 in 2011 and almost 300 g hr -1and 2012. These flow rates were comparable to maximum rates observed for other crops in Florida including, potato (200 g hr -1) (Byrd, 2012) and cotton (250 g hr -1) (Thompson, 2012). Maximum flow rates are typically st andardized according to leaf area in the literature, but flow rates have been reported for cotton (120 g hr -1), maize (150 g hr -1), and sunflower (225 g hr -1) (Loscano, 2000; Kjelgaard et al., 1997). However, when calculating sap flow on an area basis and summing over the meas urement period, the difference in planting density between the two y ears resulted in nearly identical total sap flow values: 57,199 L ha-1 day-1 and 56,560 L ha-1 day-1, for 2011 and 2012, respectively. The similarity of sap flow rates on an area basis can be explained by the offsetting changes in planting density and co rrelated canopy development. The lower planting density (2012) produced larger plants, as evidenced by the increase in stem
72 diameter, and a closed canopy must have result ed in an increase in leaf area per plant as compared to smaller plants that were planted at a higher density (2011). An increase in leaf area would produce a higher transpiration rate under optimal conditions and could reasonably explain the two-fold increas e in rate while maintaining similar flow rate when calculated on an area basis. In co mparison, the water use rates for castor were within the range for cotton (44,200 L ha-1 day-1 to 95,000 L ha-1 day-1) (calculated from Dugas, et al. 1994). Daily sap flow on an area basis and the matched daily ETo values calculated from the weather station on site oscill ated throughout the year in 2011 and 2012, with the values closely matched early in the in stallation period (55-111 DAP in 2011; 54-89 DAP in 2012) (Figure 3-4). There was evidence of an increasing trend from the beginning of collar installation up to harvest in both years. The best-fit regression for these area sap flow values in 2011 resulted in a third order polynomial, while in 2012, the regression resulted in a second order pol ynomial best-fit of the data (Table 3-1). These second and third order polynomials refl ect daily water-use patterns of the crop following an increasing trend from collar installation to late season, followed by a plateau or slight increase in water use just pr ior to removal of the co llars (Figure 3-5). This late peak in water use may be an due to the indeterminate nature of castor and an increased fruit set as compared to crops that senesce late in the season with corollary decreases in water use (partly due to the stoppage of irrigation). The calculated 10-day average Kc values for 2011 were fairly constant at approximately 1.15 until approx imately 110 DAP, when a spike to a value of approximately 1.5 until the end of the measurement period was observed (Figure 3-6).
73 Likewise in 2012, the 10-day average Kc values initially star ted around 1.15 and then showed a step-wise increase starting at DAP 90 with a value of 1.37 and increasing to a peak Kc value of 1.64 at 100 DAP. However unlike 2011, the 10-day Kc value in 2012 decreased to a fairly consistent value of 1.5 from DAP 110 through the end of the measurement period (Figure 3-6). Kc values of 1.5 ar e larger than any Kc reported by the FAO and the high range is partly due to a decrease in ETo combined with an extended irrigated growing season. The particular Kc values calculated on a 10 day basis in this study are reported in Table 3-2. The ten day Kc values calculated in this study show much higher resolution than Kc values reported by the FAO and the signific ant increase at the late season is quite different from most crops. Maize, cotton and sunflower, have a peak Kc value during mid-season and a much lower late season Kc value while other crops, such as coffee, pineapple, and olives, maintain the same Kc through mid and late season (Allen et al. 1998). Castor grown in Florida does follow the same increasing Kc trend as berseem clover ( Trifolium alexandrinum) which is grown in India and the US mid-west with an increasing Kc from 1.11 in mid-season to 1.24 in late season (Tyagi, 2003). The FAO Kc values for castor with a maximu m height of 0.3 m are 0.35, 1.15, and 0.55 for the early, mid, and late season, respectively (Table 3-3) (Allen et al., 1998). The calculated Kc values for the two seasons of th is study, based on the timeframes recommended by the FAO, were between 1. 17 (2011) and 1.20 (2012) during the midseason and 1.49 (2011) and 1.51 (2012) for the late season (Table 3-3). Based on these results, the late season Kc values proposed by the FAO may need to be adjusted for castor grown in Florida. Although the late-season Kc values for this cropping system
74 deviated from those reported by FAO, parti cularly in the late-season, a direct comparison between the two values may not be appropriate. The FAO reports Kc values based on standard irrigation practi ces and planned harvests when the seed is dryas is the case with castor and other dr y beans discontinue irrigation or wait until a killing freeze to effectively desiccate the cr op. This cessation of irrigation reduces the moisture within the seed and also lowers the Kc due to low evaporation and transpiration rates (Allen et al., 1998). The cropping system used for this study irrigated until the crop was chemically terminated with a harvest aid. Theref ore, the increasing Kc values in the late-season found in this st udy were representativ e of a crop that was still physiologically active. Fu rther, the FAO values for ca stor are based on an average crop height of 0.3 m; however, the Florida ca stor crop in this study reached a maximum height of 0.85 and 1.15 m during 2011 and 2 012, respectively, thereby likely contributing to higher overall water-use rates than that r eported by FAO. The increasing water-use pattern in the late season for Florida castor production is interesting as it may indicate that ca stor grown in this region does not have a physiological cut out. Physi ological cut out has been extensively studied in cotton and is characterized as the time in the crop life cycle when cessation or extended lapse in terminal growth occurs that typically signals the end of the effective fruiting period (Oosterhuis et al., 1996; Oosterhuis and Kerb y, 2011). An extended lapse in terminal growth was not observed in this study as the castor crop continued to flower and produce reasonable sized racemes past the tertia ry racemes. A plant that exhibits a physiological cut out will also decrease water use if the cut out also results in a decrease in activity of the photosynthetic pl ant parts (green flower s, leaves, etc.).
75 Again, castor in this study maintained its water use quantity, regardless of decreases in ETo, up until chemical termination resulting in increasing Kc values until that time. In summary, the peak transpiration for cast or in this study occurred sometime after 1300 EDT and was comparable to rates r eported for potato, cotton and sunflower. Castor sap flow rates normalized on an area basis were shown to have relatively consistent water-use values across the two years of the study. Calculated 10 day Kc values were roughly in the range of 1.11 to 1.29 for the mid-season and, contrary to expectation, increased to a r ange of 1.49 to 1.52 until chemical termination of the crop. This indicates that castor may not have a physiological cut out date as reflected by continued raceme development and increased water use. These results provide appropriate Kc values for north-central Florida and wil l aid growers in irrigation decisions when producing castor in this region. Table 3-1 Sap Flow Regression of 2011 and 2012. F values for sap flow amounts on DAP 2011 2012 Best Fit df F Value R 2 Value F Value R 2 Value First Order 1 0.2444 0.00639 9.0910** 0.141845 Second Order 2 0.3524 0.01869 9.2280** 0.254721 Third Order 3 4.1894* 0.25877 11.4633** 0.393522 ** Indicates P < 0.01 Indicates P < 0.05 Table 3-2 Florida 10-day Kc Average Season DAP 2011 2012 50-60 1.15 1.11 Mid 60-70 1.14 1.14 70-80 1.29 1.12 80-90 1.13 1.15 90-100 1.12 1.37 100-110 1.11 1.64 Late 110-120 1.49 1.52 120-130 -1.49 130-140 -1.51
76 Table 3-3 Florida Kc Values based on FAO Timeframes Planting 0-20 DAP Development 20-60 DAP Peak Growth 60-110 DAP Late Season 110-135 DAP Castor (Indonesia) 0.35 -1.15 0.55 2011 Florida Kc value Collar not installed Collar not installed 1.17 1.49 2012 Florida Kc value Collar not installed Collar not installed 1.20 1.51 Figure 3-1 2012 Daily versus His torical Solar Radiation. All Days Included (a) and Days Above Historical Average (b) Figure 3-2 Average daily sap flow rates a b
77 Figure 3-3 Average daily solar radiation
78 Figure 3-4 Seasonal Sap Flow and ET o measurements in 2011 (a) and 2012 (b) Figure 3-5 Regression of crop water fl ow per area across DAP for castor grown in 2011 (a) and 2012 (b) a b a b
79 Figure 3-6 10 Day Average Kc Values and ETo measurements for castor in 2011 (a) and 2012 (b). a b
80 CHAPTER 4 SUMMARY Results from this study suggest that additional cropping system elements that might optimize production need to be developed and tested if castor ( Ricinus communis L.) production in Florida is going to be com petitive within a potentia l US market. The maximum yields achieved in any treatment were 1,403 kg ha-1 with most treatments averaging below 1,000 kg ha-1. While these are above histor ical Florida yields and are comparable to internationally reported yields, these levels are roughly half of what has been reported for castor production in the southw estern US. Yield could be increased by increasing seed size and oil concentration as well as reducing raceme failure due to mold. This study provided novel information on the growing habits (flowering time, height, raceme number, and LAI) as well as root ing architecture that has currently not been reported for castor. The stature (hei ght and nodes below the first raceme) found in this study was suitable for most mec hanical harvesters currently being tested in Texas. The earlier flowering time for the cu ltivars grown in Florida needs to be further evaluated as yields may have been reduced due to a lack of photoassimilate allocation to the primary and secondary racemes. Interest ingly, the rooting presence in the top 10 cm of the soil profile show ed a significantly lower length and surface area, which is contradictory to previous cultural recommendat ions to avoid shallow cultivation due to the presence of a fibrous root system near the soil surfac e. In addition to possible increases in mechanical cultivation, the quick growing root system (up to 20 mm day-1) may suggest that these cultivars in Flor ida are capable of mining water and nutrients deep in the soil demonstrating possi ble drought tolerance.
81 This study also tested different produc tion inputs in an effort to develop a sustainable production system in Florida. One of the most important and perhaps surprising results of the current study is the lack of effect of PGR on the height and growth habit in either castor cultivar. Ev en when applied at different rates and different crop development times, the us e of mepiquat chloride based plant growth regulator did not affect plant height and produced conflicting effects on the photosyn thetic capacity of the crop after treatment. Due to the irregularit y of a killing freeze in Florida, the use of a harvest aid is likely to be a necessary cropping system component, and the results of this study reveal that paraquat was more e ffective than tribufos. Paraquat would be an effective harvest aid in a cropping system without a rattoon (due to isolated plant death), but regrowth noticed at 11 DAT suggests a har vest date before that time to maximize harvest efficiency. The ETc for castor cropping systems in Flori da is primarily due to increases in crop transpiration as daily soil evaporation rates were 0.07% of the lowest daily transpiration rate. Peak trans piration for castor in this study occurred between 1300 and 1415 EDT and maximum rates (between 150 g hr-1 and 300 g hr-1), which were comparable to rates reported fo r potato, cotton and sunflower. Average castor sap flow rates normalized on an area basis (56,560 L ha-1 day-1 and 57,199 L ha-1 day-1) were shown to have relatively consistent and slig htly increasing water-use values across the two years of the study. Water use throughout the season did not demonstrate the same pattern in 2011 and 2012 with a third order polynomial best-fit in 2011 and a second order polynomial best-fit in 2012. Calculated Kc values were roughly in the range of 1.1 to 1.29 for the mid-season and, contrary to expectation, increased to a range of 1.49 to
82 1.52 until chemical termination of the crop. The late season peak in water use may be due to several factors including: the i ndeterminate nature of castor, especially manifested with continued irrigation into t he late season; an increased fruit set as compared to crops that senesce; and the lack of a physiological cut-out phenomenon late in the season. Future research is needed to develop and evaluate additional management methods to increase the yield of castor grow n in Florida. This project focused on a cropping system with a single harvest, but the results of this study combined with the potential to grow castor in a rattooning syst em (data not shown) may suggest rattooning is a better cropping system for ca stor in Florida. Even if rattooning castor in Florida proves to be unsuccessful, thes e results do provide appropriate Kc values for northcentral Florida and will aid growers in irrigat ion decisions when producing castor in this region.
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90 BIOGRAPHICAL SKETCH David Neil Campbell was born in Grot on, MA and earned his bachelors degree at the University of Florida. David initia lly pursued a career in Medicine, but switched his academic and career focus to Agricult ure and Higher Education. David believes agriculture will play an increasingly impor tant role in society as both the world population increases and natural resources decrease.