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

Crop Production: conservation tillage
Education and Training: demonstration, extension, mentoring, workshop
Farm Business Management: whole farm planning, budgets/cost and returns
Pest Management: cultural control, economic threshold, mulches - killed, physical control, mulching - plastic, mulching - vegetative
Production Systems: agroecosystems, holistic management, organic agriculture
Soil Management: green manures, nutrient mineralization

Abstract:

Tropical smallholder farmers that operate under low-external-input (LEI) conditions rely upon non-intensive on-farm or locally available inputs for agricultural production; however, such resources are limited in the tropics and there is sparse data regarding the sustainability of tropical LEI agroecological systems. The primary objective of this study is to identify and evaluate tropical (warm season) cover crops and the subsequent use of cover crop residues as in situ mulch in reduced tillage agroecosystems.

Objective 1, in the U.S. Virgin Islands evaluated five tropical (warm season) cover crop species that included sunn hemp (Crotalaria juncea cv. IAC-1), sun flower (Helianthus annuus, var. black oil), bush pigeon pea (Cajanus cajan cv. BRS Mandarim), sesame (Sesamum indicum, cv. ns), and velvet bean (Mucuna pruriens (L.) DC. cv. Vine 90). Cover crops were compared and their response to mechanical termination with a roller-crimper to produce in situ mulch for weed suppression was determined.

In the U.S. Virgin Islands, sunn hemp produced the greatest biomass levels of the cover crops evaluated within the 90 day period between planting and termination. Pigeon pea produced large amounts of biomass (13,842 kg ha^-1), but was slow to develop and took 160 days to flower. Sunn hemp biomass was 7,967 kg ha^-1, and had plant tissue N and P content of 2.9% and 0.17%, that resulted in sunn hemp having the highest estimated N and P contribution potential of 231 kg ha^-1 nitrogen and 14 kg ha^-1, respectively. Both sesame and sunn hemp were effective at suppressing both broadleaf weeds and grass weeds during cover crop establishment. Sunn hemp, sesame, and sun flower were effectively terminated with a roller crimper while velvet bean and pigeon pea were not, as evidenced by substantial levels of regrowth following termination with the roller-crimper. Following termination, sesame and sunn hemp cover crop surface residue has the greatest potential for extending weed suppression for up to six weeks into subsequent vegetable crop rotations.

In Puerto Rico, sunn hemp (Crotalaria juncea L. cv. Tropic Sun) and velvet bean (Mucuna pruriens L. DC. cv. Dwarf) were evaluated as crimped legumes prior to sweet corn (Zea mays L. cv. Suresweet 2011) production and compared to conventional sweet corn production. Overall, sweet corn production systems including crimped legumes had similar corn yields and insect damage as conventional systems. Therefore, production systems utilizing legumes prior to corn production are recommended due to long-term ecological and soil quality benefits of cover crop use and reduced tillage.

Objective 2 in the U.S. Virgin Islands evaluated and compared three cover crop species to each other and to a weedy fallow in rotation with a subsequent no-till hot pepper (Capsicum chinense Jacq.) rotation where the cover crop residue was mechanically (roller-crimper) killed for in situ mulch for extended weed suppression. Cover crops tested included sunn hemp (Crotalaria juncea cv. IAC-1), sun flower (Helianthus annuus, var. black oil), and bush pigeon pea (Cajanus cajan cv. BRS Mandarim). Following cover crop termination, jalapeno peppers were no-till transplanted into cover crop residue mulch or the conventional full-till treatments. Overall, sunn hemp and sun flower provided near 100% weed suppression during the cover crop rotation. Both sunn hemp and sun flower were effectively terminated with a roller-crimper and through in situ mulch, provided similar or greater extended weed suppression for six weeks into the subsequent pepper rotation. Jalapeno pepper yields transplanted with no-till into sunn hemp and sun flower in situ mulch treatments were similar or greater than those in conventional full tillage systems.

In Puerto Rico, Objective 2 evaluated allelopathic effects of aqueous extracts of crotalaria (Crotalaria juncea (L.) cv. Tropic Sun), jack bean (Canavalia ensiformis (L.)) and pigeon pea (Cajanus cajan (L.) cv. Lazaro) was determined on seven agronomic crops: corn (Zea mays cv. Mayorbela 2011), sorghum (Sorghum bicolor), bean (Phaseolus vulgaris cv. Verano), soybean (Glycine max), cowpea (Vigna unguiculata (L.)), lettuce (Lactuca sativa (L.) cv. Nevada) and pigeon pea (Cajanus cajan cv. Dwarf) in the laboratory. Sorghum and lettuce showed growth inhibition of the hypocotyl, coleoptile and radicle when treated with the three aqueous extracts, where, jack bean aqueous extracts showed higher inhibition percentages (66% in lettuce and 49% in sorghum). In contrast, corn, bean and cowpea treated with crotalaria aqueous extracts exhibited growth stimulation.

Objective 3a in Florida and the U.S. Virgin Islands evaluated sunn hemp as a cover crop rotation with pepper production where the crop residue is either mechanically (roller-crimper) killed for in situ surface sheet mulch or is green chopped and soil incorporated to determine effects on soil quality and weed suppression in comparison to three common cultural weed management practices. The four treatments evaluated included sunn hemp residue in situ mulch (no-till), plastic film mulch (full-till), cut and carry hay mulch (full-till), and no mulch (conventional control; full-till). Each plot was divided in half and either low (hand weeding every third week) or high frequency (weekly hand weeding) weeding treatments were assigned to each plot six weeks after planting. In both FL and the USVI, pepper yields were greatest in the cut and carry hay treatment. In FL in 2013, the roller-crimped sunn hemp treatment pepper yields were similar to the plastic mulch and no mulch treatments and in 2014 were similar to the cut and carry hay but greater than the no mulch treatments. This indicates that under Florida conditions, when SH residue is utilized as mulch for subsequent pepper production, pepper yields can be similar to or greater than yields obtained by conventional mulching methods that rely upon full tilage for weed suppression. Florida, pepper yields were unaffected by weeding frequency. This indicates that regardless of the weed management system, fewer weeding events will be economically beneficial.

Objective 3a in Puerto Rico assessed integrated cropping system effects of three living leguminous mulches that included jack bean (Canavalia ensiformis), sunn hemp (Crotalaria juncea), and pigeon pea (Cajanus cajan) intercropped with Maricongo plantain. Integrating legumes as living mulch intercropped with plantain merkedly reduced weeds in between plantain rows resulting in less herbicide applications compared to conventional plantain cropping systems. Intercropped legemes between plantain rows resulted in benifits to plantain growth and establishment parameters.

Objective 3b in the U.S. Virgin Islands evaluated sunn hemp as a cover crop rotation with where sunn hemp is terminated with a roller-crimper and the resulting crop residue is evaluated as in situ mulch, in situ sunn hemp mulch plus landscape fabric, or in situ sunn hemp mulch plus hay mulch for no-till hot pepper production compared to conventional full tillage hot pepper production. Each plot was divided in half and either low (hand weeding every third week) or high frequency (weekly hand weeding) weeding treatments were assigned to each plot after pepper transplant. This project differs from objective 3a in that all experimental mulch treatments are no-till and only the conventional control treatment is full-till. Similar pepper yields were recorded for both low and high frequency weed removal sub-plots. This implies that three week weed removal intervals are generally as effective as weekly weed removal and could greatly reduce weed removal labor costs in organic hot pepper production. Generally, weed biomass in the conventional full-till system and the no-till sunn hemp mulch only treatments were similar and implies that full soil tillage does not necessarily correlate to reduced weed biomass compared to no-till vegetable cropping systems.

Overall, the sunn hemp mulch plus landscape fabric and sunn hemp mulch plus hay mulch treatments had the greatest Jalapeno yields with no differences between the no-till sunn hemp mulch and conventional full-till treatments. Serrano pepper yields were greatest in the sunn hemp mulch plus landscape fabric, SHM+hay, and SH+none treatments. Generally, the greatest pepper yields resulted from no-till in situ sunn hemp mulch plus the application of an additional mulch. This indicates that full tillage field preparation (at the expense of soil quality) is not necessary to ensure high yields when no-till soil conservation practices can be utilized in conjunction with in situ sunn hemp mulch (the addition of supplemental mulch can increase yields further) in organic hot pepper production.

Objective 4 demonstrated and transferred results from the first three objectives to local farmers, agriculture extension agents, and federal agricultural agencies throughout the USVI, PR, and Florida. In the U.S. Virgin Islands, research results and recommendations were presented at two field days that were conducted in 2014 and 2016 at the Agricultural Experiment Station. There were more than 40 participants (farmers, extension and research personnel) in attendance at each field day. In Puerto Rico, research results and recommendations were presented at two field days that were conducted in 2014 and 2015 at the Isabela Agricultural Experiment Station. There were more than 50 participants (farmers, extension and research personnel) that attended both workshops. At the University of Florida an outreach and extension workshop was conducted in 2016 at the Suwannee Valley Agricultural Extension Center near Live Oak, FL. There were a total of 60 farmers, extension agents and agricultural agency personnel that participated in the workshop.

Project objectives:

Objective 1; U.S. Virgin Islands: To evaluate five tropcial (warm season) cover crop species that included sunn hemp (Crotalaria juncea cv. IAC-1), sun flower (Helianthus annuus, var. black oil), bush pigeon pea (Cajanus cajan cv. BRS Mandarim), sesame (Sesamum indicum, cv. ns), and velvet bean (Mucuna pruriens (L.) DC. cv. Vine 90). Cover crops were compared and their response to mechanical termination with a roller-crimper to produce in situ mulch for weed suppression was determined.

Determine pre-termination cover crop biomass, plant tissue nutrient content, and the potential nutrient contribution (PNC).
Determine pre and post-termination weed biomass.
Determine post-termination CC regrowth and weed suppression.

Objective 1; Puerto Rico: To evaluate sunn hemp (Crotalaria juncea L. cv. Tropic Sun) and velvet bean (Mucuna pruriens L. DC. cv. Dwarf) as crimped legumes prior to sweet corn (Zea mays L. cv. Suresweet 2011) production and compare it to conventional sweet corn production.

Objective 2; U.S. Virgin Islands: To evaluate and compare three cover crop species to each other and to a weedy fallow in rotation with a subsequent no-till hot pepper (Capsicum chinense Jacq.) rotation where the cover crop residue was mechanically (roller-crimper) killed for in situ mulch for extended weed suppression. Cover crops tested included sunn hemp (Crotalaria juncea cv. IAC-1), sun flower (Helianthus annuus, var. black oil), and bush pigeon pea (Cajanus cajan cv. BRS Mandarim).

To evaluate three cover crops under tropical conditions produced with zero external inputs.
To evaluate the effectiveness of a roller-crimper to terminate the cover crops to produce in situ mulch, evaluate cover crop re-growth, and determine the effectiveness of cover crop in situ mulch for weed suppression following cover crop termination.
To measure the combined system effects of CC sheet mulch on no-till jalapeno pepper production after CC termination.

Objective 2a; Puerto Rico: Allelopathic effects of aqueous extracts 3.3% w/v of sunn hemp (Crotalaria juncea L. cv. Tropic Sun), jack bean (Canavalia ensiformis L) and pigeon pea (Cajanus cajan L. cv. Lazaro) was determined on seven agronomic crops: corn (Zea mays cv. Mayorbela 2011), sorghum (Sorghum bicolor), bean (Phaseolus vulgaris cv. Verano), soybean (Glycine max), cowpea (Vigna unguiculata L.), lettuce (Lactuca sativa L. cv. Nevada) and pigeon pea in the laboratory.

Objective 2b; Puerto Rico: In a greenhouse study, sunn hemp (Crotalaria juncea cv. Tropic Sun), jack bean (Canavalia ensiformis L.), and pigeon pea (Cajanus cajan L. cv. Lazaro) on phytotoxic indexes on germination percentage at three dates (4, 7 and 14-d) and dry weight (14-d) on the agronomic crops: corn (Zea mays cv. Mayorbela 2011), sorghum (Sorghum bicolor L.), bean (Phaseolus vulgaris L. cv. Verano), soybean [Glycine max L.), cowpea (Vigna unguiculata L.), lettuce (Lactuca sativa L. cv. Nevada) and pigeon pea (Cajanus cajan L.) were evaluated.

Objective 3a; Florida and the U.S. Virgin Islands: To evaluate sunn hemp as a cover crop rotation with pepper production where the crop residue is either mechanically (roller-crimper) killed for in situ surface sheet mulch or is green chopped and soil incorporated to determine effects on soil quality and weed suppression in comparison to three common cultural weed management practices.

Evaluate the cover crop sunn hemp [Crotalaria juncea cv. IAC-1 (SH)] and identify its suitability as surface mulch in reduced tillage vegetable cropping systems.
Compare in situ cover crop surface mulch to fabric mulch, hay mulch, and conventional no mulch vegetable systems for weed suppression and measure other ecosystem services.
Determine and compare jalapeno pepper quality and yield by treatment and weeding frequency.

Objective 3a; Puerto Rico: To assess integrated cropping system effects of three living leguminous mulches that included jack bean (Canavalia ensiformis), sunn hemp (Crotalaria juncea), and pigeon pea (Cajanus cajan) intercropped with Maricongo plantain.

Objective 3b; U.S. Virgin Islands: To evaluate sunn hemp as a cover crop rotation with where sunn hemp is terminated with a roller-crimper and the resulting crop residue is evaluated as in situ mulch, in situ sunn hemp mulch plus landscape fabric, or in situ sunn hemp mulch plus hay mulch for no-till hot pepper production compared to conventional full tillage hot pepper production. This project differs from objective 3a in that all experimental mulch treatments are no-till and only the conventional control treatment is full-till.

Evaluate the cover crop sunn hemp [Crotalaria juncea IAC-1 (SH)] and identify its suitability as surface mulch in reduced tillage vegetable cropping systems.
Compare in situ cover crop surface mulch to fabric mulch, hay mulch, and conventional no mulch vegetable systems for weed suppression and measure other ecosystem services.
Determine and compare jalapeno and serrano pepper quality and yield by treatment and weeding frequency.

Objective 4; All Locations: To demonstrate and transfer results from the first three objectives to local farmers, agriculture extension agents, and federal agricultural agencies throughout the USVI, PR, and Florida.

Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.