Developing Sustainable Tropical Leguminous Cover Crop and Green Manure Mulch Systems for Low-External-Input crop Production in the U.S. Virgin Islands, Puerto Rico, and Florida

Developing Sustainable Tropical Leguminous Cover Crop and Green Manure Mulch Systems for Low-External-Input crop Production in the U.S. Virgin Islands, Puerto Rico, and Florida

Summary

The primary objective of this study is to develop cover crop and green manure (CCGM) technologies to improve soil quality and provide alternative weed management strategies in tropical/subtropical vegetable production systems. Teams from Universities of Virgin Islands, Puerto Rico, and Florida initiated field trials to compare CCGM species, determine CCGM response to roller-crimper termination, and to quantify CCGM weed suppression benefits that extend into subsequent pepper rotations. Sunn hemp (Crotalaria juncea) was terminated with a roller-crimper, or mowed and soil incorporated, depending on trial and treatment. Sunn hemp surface mulch was evaluated as an alternative weed management practice and compared to conventional weed management practices. System improvements are proposed.

Objectives/Performance Targets

Each location initiated the first year of two-year trials as follows:

Objective 1. U.S. Virgin Islands and Puerto Rico. Years 1-2.

Modified: U.S. Virgin Islands: To assess five cover crops in a tropical climate and their response to termination with a roller-crimper for their suitability to form surface sheet mulch for extended weed suppression. The CCGM evaluated include; velvet bean (Mucuna pruriens L. cv. Vine 90; VB), sunn hemp (Crotalaria juncea L. cv. IAC-1; SH), pigeon pea (Cajanus cajan L. cv. BRS Mandarim; PP), sesame (Sesamum indica L. cv. ns; SE), and sunflower (Helianthus annus L. cv. Black Oil; SF).

• 2012, 2013: Cover crops will be evaluated on germination rate, establishment, plant vigor, biomass yield, plant tissue nutrient content, response to roller-crimper termination, and CCGM residue potentially available nutrient content (N, P, and K).
• 2012, 2013: Soil quality will be monitored and evaluated based upon the physical and chemical components of soil.
• 2012, 2013: Weed populations will be identified, quantified, and monitored over time to determine weed biomass changes prior to and following CCGM roller-crimper termination.

Modified: Puerto Rico: The objective of this study was to determine sweet pepper (Capsicum chinense) yield as affected by two organic inputs: Sunn hemp (Crotalaria juncea) as a legume cover crop and the commercial organic fertilizer BioFlora Dry Crumbles™ (6-6-5).

Objective 2. U.S. Virgin Islands and Puerto Rico. Years 1-2.

Modified: U.S. Virgin Islands: Evaluate and compare three tropical CC/GM species to each other and to a weedy fallow in rotation with a subsequent minimum-till hot pepper (Capsicum chinense Jacq.) rotation where the CC/GM residue is terminated with a roller-crimper to produce surface sheet mulch for extended weed suppression and to improve soil quality.

• 2012, 2013: Cover crop varieties to be tested will include sunn hemp (Crotalaria juncea IAC-1), sun flower (Helianthus annuus cv. Black Oil), and bush pigeon pea (Cajanus cajan cv. BRS Mandarim). Crops will be planted in monoculture and evaluated as a CC/GM for their beneficial contributions in rotation prior to the vegetable crop rotation (jalapeno pepper). Cover crop species will be evaluated on the same production characteristics as in objective 1; and then as surface sheet mulch resulting from roller-crimper termination. Weed suppression of the CCGM and the resulting surface mulch residue that extends into the pepper rotation will be determined and soil quality will be monitored in the CCGM followed by pepper cropping systems.
• 2012, 2013: Hot peppers will be transplanted directly into the CCGM surface sheet mulch and hot pepper production yields, plant quality, and soil quality will be measured to determine effects upon crop production characteristics.

Modified: In Puerto Rico, objectives were modified from the submitted proposal due to farmer demand for specific information regarding the use of legumes in locally-relevant crops. The following experiment was repeated in February 2014:   Contrast the effect of Crotalaria cv. Tropic sunn [Crotalaria juncea (L)] and Dwarf mucuna [Mucuna pruriens (L) DC.] crimped vs. Conventional tillage on yield of sweet corn, size of cob, insect damage and seed yield of “Suresweet” (Beaver et al., 2011).

Objective 3. Florida: Years 1-2, USVI and PR: Year 3

As proposed US Virgin Islands and Florida: Evaluate sunn hemp as a CC/GM rotation with hot pepper production where the crop residue is either mechanically (roller-crimper) killed for surface sheet mulch or is green chopped and soil incorporated to determine effects on soil quality and weed suppression in comparison to common cultural weed management practices.

• 2012, 2013: In Florida, traditional weed management treatments to be compared will include plastic mulch, local hay mulch, and no mulch (control). These treatments will be compared to sunn hemp surface mulch as an alternative weed management practice. In year 1 and 2, research will be conducted at the University of Florida Agriculture Research Station in Live Oak, Florida.

Modified: In Puerto Rico, The objective was to assess integrated systems effects of legumes [Jack bean, (Canavalia ensiformis), Sunn hemp, (Crotalaria juncea) and Pigeon pea (Cajanus cajan)] with cv. Maricongo plantain in height and pseudostem diameter, and weeds control after three months of planting, at Isabela and Corozal- Puerto Rico. Plantain was substituted for pepper at the request of area producers who desired to reduce their weed management efforts in plantain and reduce the incidence of the plantain beetle.

Objective 4. USVI, PR, and Florida. Years 1-3.

As proposed: Whole team. 2012, 2013, 2014: Demonstrate and transfer results from the first three objectives to local farmers, agriculture extension and outreach personnel, and federal agricultural agencies using hands-on, experiential training, classroom presentations, and fact sheets. The central message of this work is to demonstrate to farmers a range of opportunities regarding tropical/subtropical cover crop integration in vegetable systems for soil improvement and weed suppression in low-external-input cropping systems.

Accomplishments/Milestones

Objective 1. US Virgin Islands. The goal of this objective was to evaluate different cover crops how selected cover crops respond to termination by roller-crimper, and how well terminated residue suppressed weeds. Originally, this objective included three legumes: two cultivars of mucuna (Mucuna pruriens L. cv. Vine 90 and Dwarf) and cowpea (Vigna unguiculata cv. Iron Clay); two cover crop species widely adopted by producers in the tropics. However, based on Weiss’ examination of these species in a concurrent on-farm SARE-funded research trial, species selection was adjusted to exclude legumes poorly suited for termination with the roller crimper. Mucuna and cowpea are vining legumes that did not terminate well because they were succulent and lacked the structural carbon necessary for vascular system damage by the roller-crimper. Therefore, three new cover crop species were included in the trial including three cultivars of sunn hemp (Crotalaria juncea L. cv. IAC-1, cv. Tropic Sun, and an unnamed accession) (SH), sesame (Sesamum indicum Linn) (SE), sunflower (Helianthus annus L.) (SF), and pigeon pea (Cajanus cajan L. cv. BRS Mandarim) (PP). Velvet bean was retained as a physiological reference species that is similar in type to cowpea and lablab for area producers.

Cover crops were planted Oct 3, 2012 during the rainy season. Cover crops were inoculated with the recommended inoculant and broadcast at the following seeding rates: Mucuna at 50 lbs a^-1, sunn hemp at 45 lb a^-1, pigeon pea at 20 lb a^-1, sesame at 10 lb a^-1, and sunflower at 15 lbs a^-1. Cover crops were terminated with one-pass of a roller crimper on December 10, 2012.

Cover crops were evaluated prior to termination on plant vigor, biomass production, and weed suppression. Following roller-crimper termination; weed development, cover crop regrowth due to incomplete termination, and cover crop emergence due to seeds deposited from the recently terminated cover were monitored weekly for 12 weeks. Due to highly variable cover crop establishment for sesame, velvet bean, sun flower, and pigeon pea, this objective will likely need to be repeated in the third year to get two years of consistent data.

Modified Objective 1 Puerto Rico:

The objective of this study was to determine sweet pepper (Capsicum chinense) yield as affected by two organic inputs: Sunn hemp (Crotalaria juncea) as a legume cover crop and the commercial organic fertilizer BioFlora Dry Crumbles™ (6-6-5).

Field studies were conducted at the Agricultural Experimental Station of Lajas, University of Puerto Rico for two growing seasons (Experiment 1 and Experiment 2).  Experiments were arranged in a 2×4 factorial design that included cover crop (CC) vs. no cover crop (NCC) and four fertilization rates (0, 56, 112 and 168 kg ha^-1 N) supplied by BioFlora.

There was no significant effect of CC for Experiment 1 and 2, however, Experiment 1 indicated a trend towards reduced yields when CC was used (p=0.055).  The linear regression model indicated that 48% of the variation in total sweet pepper yield was due to fertilization in Experiment 1 and the highest mean was 10.3 t ha^-1.  In Experiment 2 no relation was found between yield and N fertilization and the highest mean total yield was 26.4 t ha^-1.  Differences in yield between both experiments could be attributed to different factors such as weather conditions, pest incidence, and field history.  

Objective 2. U.S. Virgin Islands.

Experimental Design. Treatments were arranged in a randomized complete block with three replications and included: 1. sunn hemp (Crotalaria juncea cv. IAC-1), 2. pigeon pea (Cajanus cajan cv. BRS Mandarim), 3. sun flower (Helianthus annuus cv. Black Oil), and 4. a weedy fallow check plot with conventional tillage.

Crop Management. Fields were disk-harrowed in preparation for cover crop seeding. Cover crops were broadcast seeded then rolled with a cultipacker on October 4, 2012. No external inputs were applied to the cover crops (no irrigation, fertilizer or pesticides). All covers were terminated on January 24, 2013 (112 days after planting) by a roller-crimper. Six weeks after jalapeno pepper transplanting, plots were split to a weeded and non-weeded management. One half of each plot was hand weeded at 6, 9, and 12 weeks after pepper transplant, the other half of the plot remained unweeded allowing for maximum cover crop regrowth and natural vegetation to emerge.

Data Collection and Analysis.  Data collection included an evaluation of the cover crop prior to termination and of the effectiveness of termination via degree of regrowth, and weed biomass and density to determine the weed-suppressive ability of cover crop surface mulch residue. Biomass sampling of cover crops and weeds were conducted using three randomly placed 0.25 square meter quadrats. Covers were sampled prior to cover crop termination, and any weeds that were present were separated from the cover crop and divided into monocots or dicots. Sorted plant material (cover crop, dicot weeds, monocot weeds) were dried in a forced air oven until constant weight. Biomass sampling of cover crop regrowth and weeds occurred 3, 6, 9, 12 and 15 weeks after termination. The first pepper harvest occurred on April 8, 2013 (112 days after seeding and 70 days after transplanting). Peppers were harvested from interior data rows, graded and weighed. A total of 9 pepper harvests occurred until the final harvest on June 21, 2013. Data were analysed using general linear model tests and means separated when data were significantly different at alpha = 0.05 using LS Means (SAS 9.3, Cary, NC).

Preliminary Results. Sunn hemp produced the greatest amount of biomass (6,418 kg ha^-1) followed by pigeon pea (4,429 kg ha^-1) and sun flower (2,027 kg ha^-1). Additionally, cover crop nitrogen concentration was determined for cover crop biomass. The order of significance followed biomass production as follows: sunn hemp (92 kg ha^-1 N) > pigeon pea (65 kg ha^-1 N) > sun flower (33 kg ha^-1).

Weeds were not present in sunn hemp, and total weed biomass was greater in pigeon pea (667 kg ha^-1) than sunflower (180 kg ha^-1).  At three weeks after cover crop termination, sunn hemp residue provided the greatest reduction in weed development. Sun flower was effectively killed with a roller-crimper. At six weeks after cover crop termination, sunn hemp continued to reduce weed development with fewer monocot weeds than all other treatments, and fewer dicot weeds than pigeon pea or sun flower, but similar to the control, despite some new growth emerging from incompletely terminated stems. Weeded split plots with weeds and cover crop regrowth removed at 6, 9, and 12 weeks reduced sunn hemp and pigeon pea biomass from regrowth to minimal levels. However, by 15 weeks, sunn hemp and pigeon pea regrowth in non-weeded plots were competitive with pepper and generated 1,193 kg ha^-1 and 3,849 kg ha^-1 of biomass, respectively.

Marketable pepper yield was greatest in sunn hemp treatment and similar to the check plot in both weedy and weeded splits. Marketable yield in weeded sunn hemp plots was 8,567 kg ha^-1 and was 2.5 times greater than yield in sunn hemp weedy splits. Marketable pepper yield was similar among sun flower, pigeon pea and check treatments in both weedy and weeded splits; yields from sun flower and pigeon pea treatments were one third of the yield observed from the sunn hemp treatment.

Pepper plants were not fertilized at all to reflect many of the grower practices on the islands, and the weed check plot included a split of a weedy subplot and a weed every third week subplot. The outcomes of these results in year 1 were that weeds in weedy split subplots outcompeted peppers quickly after the start of the season, and that the absence of fertilizer resulted in limited pepper yield. Therefore, in 2013, the following changes will be made: 1) all treatment plots will be uniformly fertigated with the recommended fertilization rates applied on a weekly basis for the duration of the pepper production period (@ 200 lbs N per acre split into 12 weekly applications), and 2) the pepper plot weeding frequency split subplots will be changed to a) weekly weeding and b) reduced weeding events every 3 weeks. Although significant changes to the approach will be necessary next year, results clearly demonstrated the roller-crimper effectively terminated sun flower and sunn hemp but not pigeon pea, and that sunn hemp was effective at suppressing weeds for 6 weeks after termination.

Modified Objective 2 Puerto Rico.

Valencia hired a master’s student, Eliana Martinez-Mera who provided leadership and conducted research described in Objectives 1 and 2. Weiss visited Valencia in Puerto Rico and worked with Valencia to select and order the roller crimper most suitable for Puerto Rico soils and system.

Objective 3. US Virgin Islands

No activities for this objective were planned for 2012.

Objective 3. Puerto Rico

No activities for this objective were planned for 2012.

Valencia hired a master’s student and began the process of experimental design, ordering supplies, and other preparatory activities for 2013.

Objective 3. Florida

The objective for Florida in 2012 was to evaluate sunn hemp as a CCGM rotation with hot pepper (Capsicum chinense Jaq.). Treatments were as follows: 1) surface sheet mulch of sunn hemp terminated by a roller crimper; 2) sunn hemp mowed and incorporated followed by a surface application of locally purchased Bahia hay; and 3) sunn hemp mowed and incorporated followed by an application of white on black plastic mulch. These systems were compared to: 4) mowed and incorporated sunn hemp with no mulch application. Methodology used, and the outcomes recorded will be applied to replicate trials in PR and USVI.

Experimental design and location. The Florida experiment was located on transitional organic land at the UF-IFAS Suwanee Valley Research and Demonstration Center near Live Oak, FL on an Alpin-Blanton-Foxworth fine sandy soil. Previous crops were annual rye (Secale cereale ‘FL 401’) followed by native Bahia grass. As such, all inputs and practices were consistent with the USDA’s National Organic Program. We worked closely throughout the year with our certification agency, Quality Certification Services, located in Gainesville, FL. The experimental area was marked with flags, including plots and buffer areas. Treatments were arranged in a randomized complete block design and replicated four times. Each plot consisted of three rows, five feet (1.5 m) on center for a total width of 15 ft (4.5 m) by 50 ft (15.2 m) in length. Alley ways between replicates were 18 ft (5.5 m). Total experimental area including alleys was 0.35 acre (0.14 ha).

Cover crop management. On March 27, 2012, a commercial, unnamed cultivar of sunn hemp (Kauffman Seeds, Inc., Haven, KS) was seeded to 38 lb a^-1 (43 kg ha^-1) with a Great Plains No-Till drill (606NT) at 7.5 in (19 cm) row spacing. Seed was inoculated with N-Dure Garden Blend inoculant prior to seeding. Sunn hemp was in mid-bloom on June 21, and plant height and density were uniform throughout. On June 21, 87 days after seeding, above-ground sunn hemp biomass was collected in three 0.5 m quadrat frames in border areas between replicates A and B, B and C, and C and D to avoid removing cover crop biomass from treatment areas. Sunn hemp was cut no more than 1in (2.54 cm) above soil level, dried to constant weight in a forced air oven at 104 ?F (40 ?C). Sunn hemp was terminated immediately after biomass samples were collected, and the method of termination was dependent on treatment, either roller-crimped with Treadwell’s crimper, or mowed with a rotary mower and soil incorporated with a rolling disk harrow (2 passes). A third pass with the rolling disk harrow was performed on June 29^th in all sunn hemp incorporated plots. Sunn hemp biomass on a dry weight basis ranged from 3,380 lb a^-1 to 3,893 lbs a^-1 (3,380 kg ha^-1 to 4,360 kg ha^-1).

Transplant management. On April 5, ‘Aji Dulce #2’ (Tomato Growers’ Supply, Ft. Myers, FL) was seeded to 72-cell Speedling transplant trays in compliant media (Organic Mechanics seed starting blend) in the greenhouse. Transplants were managed by the greenhouse technician, a veteran production specialist with 15 years of greenhouse experience. Trays were watered by hand with a water wand and scouted daily for signs of pests. During the third week, some seeds began to germinate, but germination was not consistent among trays. The weather in April was cloudy and cooler than normal, so tray heaters were added to increase the nighttime temperatures in the hopes of increasing the rate of development. While the heating trays did improve pepper development, the rate of growth was still insufficient to meet our planned transplant date of mid-June. Transplants were fertilized weekly with Drammatic One liquid fertilizer (4-1-1) (Dram Corporation) when root systems were established and two to three pairs of true leaves emerged. Pyganic was sprayed twice as needed for whiteflies.

Treatment establishment. Except the plastic mulch treatment, all other treatments were planted on the flat. Beds were pulled in plastic mulch plots with a tractor mounted bed shaper. Based on pre-plant soil analysis, our experimental site rated medium response for additional potassium and medium high response for additional phosphorus. Dry granular fertilizer (Ag-Life 3-2-2, Rhizogen, Woodlands, Tx) was applied by hand at a rate of 125 lb a^-1 (63.5 kg ha^-1) nitrogen (7.25 lb per bed) in two bands, and lightly incorporated with a roto tiller in all plots except those with roller-crimped sunn hemp mulch. Remaining nitrogen was to be applied through the drip using an organic-compliant fertilizer (4-1-1) following transplant establishment. Drip tape was installed in all plots. (RoDrip  12 in (30 cm) emitter spacing, John Deer, Moline IL). Bahia hay purchased from a neighboring farmer was loaded on appropriate plots at the same rate as the sunn hemp dry weight 8785 lb a^-1 (9,840 kg ha^-1) on July 2 prior to transplanting. White on black plastic mulch (1.5ml) was installed by hand on raised beds in appropriate plots, and bare fallow plots were lightly evened prior to installing drip tape (John Deere 12 in emitter spacing). We chose a plant spacing of 18” in double rows flanking a single drip line in the bed

Pepper Production. Peppers were transplanted by hand on July 2 and 3 (~12 weeks after seeding) in two offset rows per bed, with 24 in (61 cm) in-row spacing and 6 in (15 cm) from each side of the drip tape for a total of 50 plants per plot. The area was experiencing record high temperatures for several weeks prior to planting, and on July 2 and 3, air temperatures were around 98 ?F with a heat index of 105 ?F. To compensate for high rates of evapotranspiration, additional overhead irrigation at planting was provided by a water wagon at a rate of 500 g to the experimental area. 

Peppers were very slow to establish. Mortality was greatest in hay treatments (45%), followed by plastic mulch (10%) and sunn hemp (5%). Peppers were re-planted less than one week after transplanting throughout all plots to return plant densities to 50 plants per plot.

Despite excellent care from an award-winning greenhouse staff member, the Ahi Dulce did not perform well. Transplants were approximately 4 in tall and generally had three to four sets of true leaves. Because the other two sites were also using Ahi Dulce, we maintained our plan and transplanted what we had. For weeks preceding planting day, Live Oak and all of Florida was experiencing near record temperatures daily. Soils were extremely dry, and beds were wetted with 300 gallons of water delivered by a water truck prior to placing transplants. After three weeks of production including daily irrigations to field capacity and a light application of liquid fertilizer injected in drip lines However, the stress of volunteer Bahia emergence in the Bahia hay plots, compromised transplants, and extreme weather conditions resulted in a crop failure. After consulting the rest of the team, it was decided to abort the year rather than continue to accrue expenses.

Whole Team Objective 4.

The project team met by conference call on March 22, 2012. Stuart Weiss led a team meeting by phone of all project participants and technical support staff to determine methodology, review timeline and milestones. Plot maps and specific methodologies were drafted and circulated among the team and finalized prior to initiating field preparations to discuss the reviewers’ comments to the proposal, make the necessary adjustments, and discuss the details of cover crop termination, crop management, data collection, and analysis. To minimize differences among experiment locations, the team decided to use the hot pepper ‘Aji Dulce’, a popular aromatic pepper with low capsaicin content used in Latin American dishes.

For next year, several changes will be made to minimize risk to crop failure, improve the quality of our data, and to make the projects more culturally relevant to the farmers we serve and their buyers. These changes were discussed among the team, and presented above in their respective locations and objectives.

Impacts and Contributions/Outcomes

U.S. Virgin Islands

Several key observations were made the first year with serious implications for subsequent years in this project. Cover crops can be a valuable management tool in the tropics that require few if any external inputs. Sunflower and sesame performed well as cover crops and both were successfully terminated with a roller-crimper. Cover crop re-growth may cause weed problems when using a roller-crimper for termination of specific cover crop species that includes succulent leguminous CCGMs such as velvet bean in tropical or extended warm season environments. For indeterminate cover crops, roller-crimper termination may not be viable without additional management. Finally, surface sheet mulch resulting from cover crops terminated with a roller-crimper can be used for natural weed suppression and to conserve soil quality for subsequent crop rotations. These observations were disseminated informally to farmers, researchers, and NRCS technical service providers during the year.

Results from Objective 2 were presented at the 2013 national Agronomy, Crop Science, and Soil Science conference in a presentation titled “Tropical cover crop mulch systems for low-external-input reduced-tillage crop”.

Puerto Rico

There has been an increase in the purchase of sunn hemp seeds produced by our program and an increased demand for Cannavalia seeds. Farmers have adopted the use of cannavalia for organic banana production. Through farm demonstration visits, farmers have shown interest in the use of both sunn hemp and other legume cover crops (e.g., Cannavalia ensiformes) in plantain and papaya production. One such study is being supported by NRCS to produce plantains in the Gurabo valley using both sunn hemp and cannavalia as cover crops. An on-farm study will be initiated in March 2014, at farmer cooperator Carlos Gonzalez to assess the effect of three cover crops (sunn hemp, cannavalia and pigeon pea).     

Florida, Objective 3.

Four essential production lessons were learned in Florida during year 1. First, Ahi Dulce is not an appropriate cultivar for Florida conditions. Transplants were extremely slow to emerge despite expert greenhouse care, and never developed properly. A different cultivar will be selected for 2013. Second, it is difficult to assess the degree of re-germination of hay, and although the farmer assured us it was cut prior to seed maturity, we experienced significant germination of Bahia in our plots resulting in nearly 100% mortality of peppers in that treatment. To avoid this in the future, we have decided to add a rotation of winter cereal rye (Secale cereale L.) ahead of sunn hemp to our experiment and bale the straw at the appropriate time prior to mature seed formation. We will use the cultivar FL 401 that is well-adapted for our area and is capable of significant biomass production. Third, the application of hay prior to transplanting may have interfered with transplant establishment by reducing air circulation around the plant, retaining excessive heat in the area around the transplant. We will apply hay after transplants have firmly established, approximately 10 days after transplanting. Finally, plastic mulch and drip irrigation need adjustments for this system. Hand application of plastic mulch did not result in a tight fit around the bed, and drip emitter spacing was too far apart to provide sufficient water to the pepper plant density we planned. These observations were shared informally throughout the year at various extension events and to visiting researchers and farmers at the experimental site in Live Oak.     

Whole Team, Objective 4

In this first year, our impact and contributions to producers and consumers has been limited to those direct interactions teams in each location have had with others in our own communities as described below.

• Presentation – Tropical Cover Crop Mulch Systems for Low-External-Input Reduced Tillage Crop Production.
• Abstract – Tropical Cover Crop Mulch Systems for Low-External-Input Reduced Tillage Crop Production.

Collaborators: