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University of Florida | Journal of U ndergraduate Research | Volume 13 Issue 2 | Spring 201 2 1 An Evaluation of Clovers as Potential Winter Cover Crops in North Florida Kaylene Sattanno College of Agricultural and Life Sciences, University of Florida Cover crops are crops planted between cycles of cash crops that provide benefits to the farm. Clove r ( Trifolium spp. ) is a leguminous crop that can contribute nitrogen to subsequent crops. The objectives of this study were to assess four lines of clovers adapted to the Southeastern US for use as potential winter cover crops in North Florida and determ ine if planting date is a factor in their success. In this experiment, we expected variation in performance between the clover lines, planting dates, and clover line x planting da te. Germination tests were performed on each line to verify the seeds would g erminate at elevated temperatures. In the field, the experimental design was a randomized complete block with a factorial arrangement of treatments of four clover lines, two planting dates, and four reps. We experienced variation in performance between clo ver lines and variation in performance between planting dates, but no variation in clover line x planting date performance. After experiencing variable rain patterns during the fall and winter, we determined that clover establishment and stand maintenance is risky without irrigation. To increase the probability of successfully evaluating clovers as potential winter cover crops in North Florida, the clovers should be irrigated, as needed, to ensure st and maintenance after establishment. I NTRODUCTION Cover crops are crops planted between cycles of cash crops that provide internal and external benefits to the farm. Incorporating a cover crop into a crop production system has been shown to contribute to one or more of the following: reduced soil erosion (Flach 1990) reduced runoff (Hoyt, Monks, & Monaco, 1994) and nutrient leaching (Stivers & Shennan, 1989), reduced pest pressure (Crow Guertal, Rodriguez, & Kabana, 1996; McSorley, Dickson, and Debrito, 1994; McSorley & Dickson, 1995; Mojtahedi, Santo, & Ing ham, 1993; Creamer, Bennett, Stinner, & Cardina 1996; Sanford & Hairston, 1984 ; Weston, Harmon, & Mueller, 1989) increased soil fertility (Fortuna, Harwood, Kizilkaya, & Paul 2003) and improved soil physical properties (Barber & Navarro, 1994; Wilson, L al, & Okigbo, 1982) There is increasing interest among farmers in using leguminous cover crops because they typically obtain most of their nitrogen (N) through biological fixation and can contribute N to subsequent cash crops ( Flach, 1990; Wang McSorley, & Gallaher, 2004). Compared to grass cover crops, legumes typically have a lower carbon to nitrogen (C:N) ratio, leading to faster resid ue decomposition and release of nutrients contained in the residues but l egume residues do not usually sustain weed co ntrol as long as grass residues (Managing Cover Crops Profitably, 2009). Farmers in Florida lack a variety of cool season legumes adapted to the Southeast mainly due to the high dependence of cool season legumes on soil moisture (Stanley, Chambliss, Blou nt, & Adjei, 20 06 ). O ne genus that is well adapted is clover ( Trifolium spp. ) As a cover crop, it has been shown to reduce pests and diseases and contribute N to subsequent crops and it show s potential as a weed suppressor (Managing Cover Crops Profitabl y, 2009; Hollander Bastiaans, & Kropff 2007). In Florida, c lovers are traditionally planted between Oct ober 1 and Nov ember 15 and complete their annual life cycle between April and May (Stanley et al., 2 006 ). T o be an effective winter cov er crop the clo vers should be sown in mid September and killed prior to the spring cas h crop plantin g in early March Planting the clover in September allows the crop more time to accumulate biomass and N before the early spring kill though the soil temperature in Se ptember is elevated compared to October and November To ensure the clover lines chosen for this experiment would adequately germinate at elevated temperatures, germination tests were performed at increasing heats Upon verification, the clover lines were evaluated in the field for two planting dates: September 17 and November 17 The four lines examined were FL 2,4 D, FL 4X, Southern Belle (SB) and Dixie. FL 2,4 D is an experimental diploid red clover ( Trifolium pretense L. ) line It has been shown to fl ower about three weeks earlier than other lines of clover, so, theoretically, it should accumulate more N than the othe r lines before the spring kill FL 4X is an experimental tetraploid red clover line. It has larger seed s than the other lines of red cl over tested, so, theoretically, it should exhibit greater seedling vigor which determine s the potential success of the seeds during germination and emergence Southern Belle is a diploid red clover cultivar that is the most wid ely grown red clover in
KAYLENE SATTAN N O University of Florida | Journal of U ndergraduate Research | Volume 13 Issue 2 | Spring 201 2 2 Flor ida. It is superior to all other known red clover cultivars in resistance to root knot nematode species ( Meloidogyne arenaria M incognita M javanica ) and provides early spring growth (Quesenberry Blount, Dunavin, & Mislevy 2005) Dixie is a diploid c rimson clover ( Trifolium incarnatum L. ) cultivar that is known for its superior forage production in the Southeastern US (Stanley et al., 20 06 ) All of the red clovers lines were bred from Cherokee red clover, which is adapted to the Southeastern US and shows root knot nematode resistance, (Quesenberry Prine, Ruelke, Dunavin, & Mislevy, 1993) The objectives of this study were to assess four lines of clovers adapted to the Southeastern US for use as potential winter cover crops in North Florida and det ermine if planting date is a factor in their success To be a prospective cover crop the clover line should provide quick emergence, rapid canopy coverage, good weed suppression, high biomass production, and sufficient nitrogen accumulation to benefit a s ubsequent crop. In this experiment, w e expected variation in performance between the clover lines planting dates, and clover line x planting date interaction s M ETHODS Germination Tests The average soil temperature at the nearest Florida Automated Weath er Network ( FAWN ) Station (Alachua) during September 2008 and 2009 wa s 80F, which was about 10 to 15F warmer than the average soil temperature in November 2008 and 2009 (Figure 1). G ermination tests were performed fo r 6 d ays each under three temperature treatments: 65F, 75F, and 85F. Three replications of 50 seeds from each line were evaluated for each treatment. Seeds were placed on two sheets of filter paper in sterilized petri dishes and moist ened with water Petri dishes were placed in a seed germinator with controlled temperature and light settings. During each treatment, the germinator was kept at a constant temperature with 12 h our light and 12 h our dark cycles. Petri dishes were checked each day to ensur e the filter papers remained moist throughout the experiment. After six days, the number of germinated seedlings was counted, a n average germination percentage was calculated, and adequa cy of germination at elevated temperatures was determined Adequate g ermination at elevated temperatures was defined as an average germination percentage greater than 85% at 75 F and 85 F Figure 1. 10cm soil t emperature ( F) bi monthly a verage at the FAWN Alachua Research Station from September 1 to Nov ember 15 i n 2008 and 2009. In 2008, the average 10cm soil temperature was 83 F during Sept ember 1 15 79 F during Sept ember 16 30, 77 F during Oct ober 1 15, 71 F during Oct ober 16 31, and 68 F during Nov ember 1 15. In 2009, the average 10cm soil temperature was 81 F during Sept ember 1 15, 81 F during Sept ember 16 30, 79 F during Oct ober 1 15, 74 F during Oct ober 16 31, and 70 F during Nov ember 1 15. 83 79 77 71 68 81 81 79 74 70 60 65 70 75 80 85 Sept 1-15 Sept 16-30 Oct 1-15 Oct 16-31 Nov 1-15 Average 10cm Soil Temperature (F) Date Alachua, 2008 Alachua, 2009
C LOVERS AS P OTENTIAL W INTE R C OVER C ROPS University of Florida | Journal of U ndergraduate Research | Volume 13 Issue 2 | Spring 201 2 3 Field Analysis In the field, t he experimental design was a randomized complete block with factorial arrangement of treatments of four clover lines and two planting dates ( Sep tember 17 and Nov ember 17 ), and four reps (Figure 2) The field was located at the Agronomy Teaching Plots on the U niversity of F lorida Gainesville Campus. Each plot was 1.52m x 4.57m Prior to each planting, the field was disked and cultipacked. The seeds were inoculated with Rhizobium trifolii and broadcast seeded at a rate of 29.65 lbs/ ha for red clover and 37.07 lbs/ ha for crimson clover. Immediately after planting, the field was cultipac ked and watered for one hour. At three five and seven d ays after planting (DAP), the newly seeded plots were watered for about one h our to help with germination and establishment. After seven d ays n o more water was supplemented, in order to mimic a typical cover crop scenario. Ten DAP, a 1m 2 rectangle of PVC pipe was thrown at five random times in each plot. Percent clover ground cover and percent weed ground cover were estimated after each throw and averaged to determine the average percent clover and average percent weed ground cover. Dixie B1, P1 Dixie B1, P2 Dixie B2, P2 Dixie B2, P1 SB B3, P2 SB B3, P1 2,4 D B4, P2 2,4 D B4, P1 SB B1, P1 SB B1, P2 SB B2, P2 SB B2, P1 2,4 D B3, P2 2,4 D B3, P1 4X B4, P2 4X B4, P1 2,4 D B1, P1 2,4 D B1, P2 4X B2, P2 4X B2, P1 4X B3, P2 4X B3, P1 Dixie B4, P2 Dixie B4, P1 4X B1, P1 4X B1, P2 2,4 D B2, P2 2,4 D B2, P1 Dixie B3, P2 Dixie B3, P1 SB B4, P2 SB B4, P1 Figure 2. Field l ayout R andomiz ed complete block design with a factorial arrangement of treatments, planting dates, and 4 reps (B=block, P=planting date) Data Analysis Percent clover and weed ground cover d ata were statistically analyzed by performing a n analysis of variance (ANOVA). R ESULTS Germination Tests From 65 F to 85 F, the ave rage germination percentage (avg. germ %) of Dixie drop ped from 97 to 93%, Southern Belle (SB) drop ped from 91 to 88%, FL 4X increase d from 86 to 91%, and FL 2,4 D drop ped from 93 to 91% (Table 1) At 75F and 85F, each clover line had greater than 8 7 % av g. germ ( Table 1 ). Table 1 Average P ercent C lover G ermination for E ach C ultivar and Treatment Temperature Treatment Temperature C ultivar Avg Germ % 65 F Dixie 97 SB 91 4X 86 2,4 D 93 75 F Dixie 87 SB 87 4X 89 2,4 D 91 85 F Dixie 93 SB 88 4X 91 2,4 D 91
KAYLENE SATTAN N O University of Florida | Journal of U ndergraduate Research | Volume 13 Issue 2 | Spring 201 2 4 Field Analysis There were significant effects of clovers and planting dates on % clover ground cover, but no effect of clovers or planting dates on % weed ground cover FL 2,4 D had higher % clover ground cover for both planti ng dates and the Nov ember 17 p lanting date had higher % clover ground cover than the Sep tember 17 planting date (Table 2) Table 2. Average P ercent G round C over of C lovers and W eeds 10 DAP for E ach C ultivar, R eplication, and Planting % Clover Ground Cover % Weeds Ground Cover Replication Cultivar Planting 1 Planting 2 Planting 1 Planting 2 1 FL 4X 55 55 10 5 Dixie 65 70 10 5 FL 2,4 D 70 75 10 10 SBC 60 60 15 10 2 FL 4X 85 90 5 15 Dixie 70 75 10 10 FL 2,4 D 75 7 5 10 10 SBC 80 85 10 5 3 FL 4X 65 70 10 15 Dixie 60 70 10 10 FL 2,4 D 80 90 5 10 SBC 70 85 5 10 4 FL 4X 65 70 10 10 Dixie 70 70 10 5 FL 2,4 D 60 65 10 5 SBC 60 60 5 5 F AWN Weather Data Average air and so il temperature data and rainfall data collected by FAWN were analyzed to determine their interactions with germination, percentage clover ground cover, and percentage weed ground cover in the field experiment. Figure 3 demonstrates that the average 60 cm ai r temperature from September to November 2010 was very close to the 2000 2011 average. From December 2010 to January 2011, the average air temperature was 5 F to 10 F cooler than the 2000 2011 average During February and March 2011, the average air temper ature was 2F to 3F warmer than the 2000 2011 average (Figure 3) In general, the average air temperature fluctuates within 5 F of the 2000 2011 average (Figure 3).
C LOVERS AS P OTENTIAL W INTE R C OVER C ROPS University of Florida | Journal of U ndergraduate Research | Volume 13 Issue 2 | Spring 201 2 5 Figure 3. 60cm Air Temperature (F) Monthly Average at the FAWN Alachua Research St ation Figure 4 demonstrates the average 10cm soil temperature from September to November 2010 was nearly identical to the 2000 2011 average. From December 2010 to January 2011, the average soil temperature dropped about 5F below the 2000 2011 average During February and March 2011, the average soil temperature is almost the same as the 2000 2011 average (Figure 4). In general, the average soil temperature fluctuates within 5F of the 2000 2011 average (Figure 4). Figure 4. 10cm Soil Temperatu re (F) Monthly Average at the Alachua Research Station. Figure 5 demonstrates the average monthly rain total respectively. The 2000 2011 average for September t month, respectively (Figure 5). The average monthly rain 2000 2011 average in some years (Figure 5). 0 10 20 30 40 50 60 70 80 90 Sept Oct Nov Dec Jan Feb Mar Avg 10cm Soil Temperature (F) Month 2001-2002 2006-2007 2009-2010 2010-2011 Annual Average (2000-2011) 0 10 20 30 40 50 60 70 80 90 Sept Oct Nov Dec Jan Feb Mar Avg 60cm Air Temperature (F) Month 2000-2001 2001-2002 2009-2010 2010-2011 Annual Average (2000-2010)
KAYLENE SATTAN N O University of Florida | Journal of U ndergraduate Research | Volume 13 Issue 2 | Spring 201 2 6 Figure 5 Mon thly Rain Total (in) at the FAWN Alachua Research Station. Data shows that the average monthly rain total is highly variable, fluctuating up to 20 inches above the 2000 2011 average in some years DISCUSSION Based on the germination tests car ried out in the growth chambers, all four clover lines displayed adequate germination at all three temperatures tested. The highest temperature tested (85F) was approximately the same as the average soil temperature based on the FAWN data for September, w hich allowed us to pursue a field evaluation of the clovers and implement an early planting date of Sep tember 17 2010. The first planting had an average stand of 68% clovers 10 DAP (Sep tember 27 ) and a sli ghtly better stand at 14 DAP ( Oct ober 1 ). Early in October, aggressive weeds, such as purple nutsedge ( Cyperus rotundus ) and pigweed ( Amaranthus spp. ), began out competing the clover and the clover started desiccating. This probably occurred because purple nutsedge, a perennial, is better adapted to fall growing conditions than clover and likely already developed an extensive root system by the time the rain ceased. Thus, it was better able to exploit the soil profile than clover, which would have only developed a shallow root system this early in the seas on. Pigweed is a summer annual so, for similar reasons as purple nutsedge, it was able to out compete the clover, especially when the rain ceased to fall. At 30 DAP ( Oct ober 17 ), clover was no longer present. The lack of competitiveness for water and nutri ents during the first planting was likely due to the lack of rainfall received during September and October, which was nearly past ten years. Rainfall is the expected cause of poor stand maintenanc e because it fluctuated vastly below the average while the other environmental factors varied minimally. The initial supplemental irrigation allowed the clover to germinate and produce its first or second trifoliate leaf, but because of a lack of rainfall, the clovers did not persist. The s econd planting took place on Nov ember 17 2010 and had a mildly better stand ( 73%) than the first at 10 DAP ( Nov ember 27 ). The clover out grew the weeds more effectively than at the first planting until about 30 DAP (Dec em ber 16 ), when the weeds began to out compete the clover and the clover eventually diminished by 45 DAP (Dec ember 31 ). The most predominate weed during the second planting was wild radish ( Raphanus raphanistrum ), a winter annual. The second planting likely failed due to the lack of rainfall received during November and December averages from the past ten years. The below average air temperatures experienced during late November to mid January may have also contributed to poor clover growth and competitiveness during this time, but it is expected that rainfall is the more plausible cause due to its large flux below the average while other envir onmental factors varied slight ly During the first planting, clov er was competing with warm season weeds, which tend to have a faster growth rate and accumulate more biomass over time than cool season crops. Even though clover germinated and emerged well, they were at a disadvantage co mpared to the warm season weeds. Th is was further exacerbated by the lack of soil moisture. Weed species also tend to persist despite environmental stresses, which were evident when the entire clover crop was lost in the middle of each planting, but the weeds carried on. After repeated fros ts in November 2010, most of the warm season weeds were eliminated due to their low frost tolerance or dormancy ; thus, the clovers main competitors during the second planting were cool season weeds. Since these are generally less aggressive in growth tha n warm season weeds, the clovers had a longer period of competition free time to help get established before competing for soil resources. This shows how 0 5 10 15 20 25 Sept Oct Nov Dec Jan Feb Mar Rain Total (in) Month 2000-2001 2002-2003 2005-2006 2010-2011 Annual Average (2000-2011)
C LOVERS AS P OTENTIAL W INTE R C OVER C ROPS University of Florida | Journal of U ndergraduate Research | Volume 13 Issue 2 | Spring 201 2 7 planting date greatly dictates the weed environment that will likely be present, as well. In this stud y, we experienced variation in performance between clover lines and variation in performance between planting dates, but we did not experience variation in clover line x planting date performance Although FL 2,4 D showed superior ground covera ge at 10 DAP for both planting dates, it is difficult to conclude that it is superior due to complete stand losses later in the plantings. Planting date two had a higher percentage of clover ground cover than planting date one, but since both plantings fa iled it is difficult to determine if planting date is a factor in the success of clovers as winter cover crops. Typically, farmers in this region use rye ( Secale cereale ) or annual ryegrass ( Lolium multiflorum ) as winter cover crops rather than clover beca use clovers are more reliant on soil moisture than rye or annual ryegrass, and crop failure is thus less likely with these species. As a result of variable rain patterns during the fall and winter, clover establishment and stand maintenance is risky withou t irrigation. Future clover studies, in regards to weed suppression and cover crops, should be performed with soil moisture defined as the limiting factor inhibiting success throughout the season. To increase the probability of successfully evaluating clov ers as potential winter cover crops in North Florida, the clovers should be irrigated as needed to ensure stand maintenance after establishment. ACKNOWLEDGEMENTS This research was funded by the University of Florida University Scholars Program, 2010/201 1. REFERENCES Barber, RG & Navarro, F. 1994. 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