Promoting Tropical Cover Crop Mulch Systems for Minimum-Till Crop Production in the U.S. Virgin Islands

Final Report for OS11-062

Project Type: On-Farm Research
Funds awarded in 2011: $14,957.00
Projected End Date: 12/31/2014
Region: Southern
State: U.S. Virgin Islands
Principal Investigator:
Dr. Stuart Weiss
Tarleton State University
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Project Information


Tropical cover crops representing three morphological plant types were tested followed by the effect of no-till roller-crimper termination (without herbicide) to provide residual surface sheet mulch for extended weed suppression. Cover crops with rapid soil cover and high levels of shoot biomass suppressed weeds prior to termination and included the legumes sunn hemp, lablab, and cowpea; and the grasses sorghum sudangrass and pearl millet. Of the cover crop cultivars tested, only sunn hemp was successfully terminated using a roller-crimper resulting in minimal cover crop regrowth with a sufficient quantity of vegetative crop surface residue that effectively suppressed weeds after termination.    


Virgin Island’s farmers face unique challenges to sustainable agriculture as a result of geographic, environmental, and socio-economic conditions that exist in the USVI. Low-external-input farming is a reality for farmers in the USVI because conventional agricultural inputs are costly or difficult to acquire.  Farm size is classified as small (<$250,000/year gross annual income) with 63% of farms totalling 9 acres or less and 81% of farms totalling 19 acres or less (USDA, 2007). 

Tropical and subtropical environments pose specific challenges for the management of soil quality, agricultural pests, and water resources. Virgin Island’s farmers have limited options to address these management concerns. Rainfall in the USVI is bimodal with an extended dry season which can last up to six months. Both surface and subsurface ground water is severely limited and farmers rely predominantly upon precipitation for agronomic production. Water conservation is practiced by all farmers and micro-irrigation is relied upon with water sourced from harvested rainwater that is stored in tanks/ponds or pumped from shallow wells. In the USVI, the supply of sufficient soil moisture levels for crop production during the dry season often limits crop production to micro-irrigated fields and requires the growing of agronomic crops, such as cover crops that have a high water demand, to coincide with the rainy season. The rainy season typically lasts from August through November and is associated with the height of the Atlantic hurricane season.

In areas of the world that do not have access to reliable, readily available, or economically feasible external sources of synthetic or organic agricultural inputs, as is the case in the USVI, alternative agricultural production systems based on local resources must be utilized. Imported synthetic fertilizers and pesticides are generally 2-to 3-times more expensive than that of prices in the continental USA. Conventional fertilizers and pesticides require costly specialized application equipment to which USVI’s farmers have little or no access. Synthetic fertilizers/pesticides and bulk organic soil amendments are not economically feasible for smallholder farmers in the USVI and are often not available at all. Therefore, smallholder farmers must utilize alternative production practices to maintain soil fertility and reduce pest incidence. Alternative low-external-input management practices readily available to smallholder farmers include cover crops, sheet composting, crop rotation, and conservation tillage technologies. Cover crop and green manure systems are one of the most promising technologies which farmers could adopt to support sustainable soil fertility levels, and agricultural improvement (Snapp et al. 1998). In order for this to be put into practice, protocols for cover crop management along with the resulting crop residue as surface mulch for use in conservation tillage, low-external-input cropping systems is needed.  

 Crop rotation, cover crops, nitrogen fixation by legumes, conservation tillage, and organic mulch from plant residues are all considered sustainable agriculture management techniques, and when employed in tandem, result in a production system with increased resilience and overall sustainability. Sustainable systems promote multiple crop rotations per year which increase biodiversity.

The use of leguminous cover crops can promote nitrogen fixation via a symbiotic relationship with mycorrhizum bacteria that can convert atmospheric N2 into plant available NO-3.  Cover crops have the ability to increase nutrient recycling and their residues result in nutrient mineralization into labile forms that would otherwise not be available to crop roots alone (Marchner 1998). In the tropics, biologically fixed N from legumes can supply greater than 110 kg N ha-1 and have been shown to achieve crop yields equivalent to yields in conventional synthetic fertilizer-driven systems (Tonitto et al. 2006). Smithson and Giller (2002) found that the utilization of legume cover crops can reach levels up to 450 kg of N per ha-1 crop-1. At this level of N production, legume based cover crop systems in the tropics can meet crop N requirements if N is conserved and environmental losses are minimized. 

Decomposition rates occur much faster in tropical climates due to elevated air and soil temperatures, as the annual mean temperature on St. Croix is 28.3°C with a mean high temperature of 32.8°C (Godfrey and Hansen 1996). Nitrogen mineralization and volatilization increases due to higher ambient temperatures which results in greater N loss for warm climates, compared to cooler climates. Soil temperature plays an important role in soil microbial populations that aid in organic matter decomposition and nutrient cycling, as biodiverse active soil can increase organic matter decomposition and speed organic N mineralization rates (Smithson and Giller 2002). High rainfall can further exacerbate N losses through increased N leaching. Conventional tillage practices greatly increase the amount of soil particle surface area in contact with environmental elements, resulting in increased N loss. Therefore, conservation-till systems that include cover crop residues may greatly reduce N and other nutrient loss through decreased soil temperatures, decreased atmospheric soil particle exposure, and by slowing the rate of water infiltration into the soil (Akanvou et al. 2001; Marchner 1998). 

In repeatedly tilled soils beneficial soil organism populations are decreased due to organic matter exhaustion, and in these cases it is more likely that harmful species of bacteria, fungi and nematodes will develop in the root zone (Sullivan 2003); thereby, increasing the reliance on fungicides and pesticides. Organic mulch from cover crop residues left on the soil surface creates "sheet composting" that more efficiently converts the carbon in the crop residue into soil organic matter (Hoorman et al. 2009; Sullivan 2003). In comparison, mowing or chopping the residue increases decomposition and percent transformation of organic molecules into carbon dioxide. Mowing or chopping the cover crop residue may result in the production of less soil organic matter than what would be produced from the same quantity of cover crop biomass if the cover crop would have been killed with a roller-crimper and left as a surface mulch (Curran et al. 2010; NRCS 2002). Therefore, overall sustainability of the agriculture production system can be increased by the use of improved tropical cover crop rotations where the resulting biomass residue is utilized as an organic surface mulch in conservation-till cropping systems.  

Cover crop benefits to agroecosystems are well documented, but the adoption of cover crops become even more important in tropical and subtropical climates where soil degradation occurs at an accelerated rate compared to temperate climates. This is attributed to 12 months of continuous hot and humid conditions and a lack of seasonal changes resulting in elevated air and soil temperatures, increased solar radiation, high evapotranspiration and soil moisture loss, increased nutrient volatization, rapid organic matter decomposition, and increased soil macro and microorganism activity. Conservation-till, mechanical-kill systems for cover crops that utilize roller-crimper technologies have proven to be cost efficient, all while increasing soil organic matter, improving overall soil quality, and providing weed suppression (Curran et al. 2010) . Roller-crimper implementation that mechanically kill tropical cover crops by "rolling" and "crimping" plant material into surface residue results in an organic surface mulch layer that creates an organic soil cover to reduce soil erosion, lower soil temperature, reduce soil nutrient loss, reduce weed germination and development, and increase soil moisture compared to conventional tillage practices that fully incorporate cover crops that require mechanized soil disturbance.

Roller-crimper technology was developed in temperate climates where either a winter or summer kill assists in the termination of the cover crop. This is not an option in tropical/subtropical climates and many cover crops have not been evaluated under tropical conditions for termination with a roller-crimper without the use of herbicides. Additionally, the resulting vegetative regrowth potential of cover crops has not been documented and needs to be quantified to determine which cover crops are adaptable for use with a roller-crimper. This project provides crucial information on tropical cover crops and their ability to be roller-crimper terminated in tropical/subtropical cropping systems.

Literature Cited

Akanvou, R., L. Bastiaans, M. J. Kropff, J. Goudriaan and M. Becker. 2001. Characterization of growth, nitrogen accumulation and competitive ability of six tropical legumes for potential use in intercropping systems. J. Agronomy & Crop Science. 187: 111-120.

Curran W., M. Ryan, and S. Mirsky. 2010. Cover crop rollers for Northeastern grain production. Penn State University USDA?ARS. Retrieved from:

Godfrey, R. W. and Hansen, P. J. 1996 Reproduction and milk yield of Holstein cows in the US Virgin Islands as influenced by time of year and coat color. Arch. Latinoam. Prod. Anim. 4:31-44

Hoorman James J.  Alan Sundermeier,  Rafiq Islam, Randall Reeder. 2009. Using cover crops to convert to no-till. Ohio State University: Agriculture and Natural Resources, Fact Sheet. Available at:

Marchner, H. 1998. Soil-root interface: biological and biochemical processes. Soil Chemistry& Ecosystem Health, Soil Science Society of America.

Smithson, P.C., and K.E. Giller. 2002. Appropriate farm management practices for            alleviating N and P deficiencies in low-nutrient soils of the tropics. Plant and Soil. 245.1: 169-180.

Snapp, S.S., P.L. Mafongoya, and S. Waddington. 1998. Organic matter technologies for integrated nutrient management in smallholder cropping systems of Southern Africa. Agric. Ecosyst. Environ. 71: 185-200.

Sullivan, P. 2003. Overview of Cover Crops and Green Manures. NCAT/ATTRA Publication No. IP 024. Retrieved from:

Tonitto C., M.B. David, and L.E. Drinkwater. 2006. Replacing bare fallows with cover crops in fertilizer-intensive cropping systems: A meta-analysis of crop yield and N dynamics. Agriculture, Ecosystems and Environment. 112: 58-72. 

U.S. Department of Agriculture. 2007 Census of Agriculture.  National Agriculture Statistical Service. Virgin Islands of the United States. Vol. 1. Geographic area series. Part 54. U.S. Summary and State data.  USDA, Washington, DC. AC07-A-54

USDA-NRCS. 2002. U.S. Department of Agriculture, Natural Resource Conservation Service. Soil Quality Institute. Technical Note No. 13. The Knife Roller (Crimper): An Alternative Kill Method for Cover Crops. Retrieved from:


Project Objectives:

This Southern SARE On-Farm grant provided the financial resources necessary to evaluate promising tropical cover crops, evaluate and demonstrate a custom built roller-crimper for advances in alternative tropical cover crop management practices, to quantify cover crop response to termination with a roller-crimper, and to measure the effectiveness of the roller-crimper to suppress cover crop regrowth and weed development following cover crop termination. Specific project objectives are as follows: 

Key performance targets include:

  1. To conduct and demonstrate on-farm cover crop research at Sejah Farm, St. Croix, USVI.
  2. To conduct on-farm cover crop research that tests roller-crimper technology to increase knowledge for the integration of conservation-till tropical cover crop systems.
  3. To develop recommendations for farmers for the use of tropical cover crop rotations that integrate roller crimper termination to reduce tillage and suppress weeds in vegetable production systems.

Project Objectives:

  1. To construct a roller-crimper from locally available recycled materials for use in on-farm research.
  2. To evaluate and compare five tropical crop species as cover crops by measuring and determining key cover crop performance indicators prior to termination (establishment rate, vegetative biomass, plant vigor, and plant tissue quality.
  3. To measure the selected cover crops ability to suppress weeds prior to termination.
  4. To determine the effectiveness of using a roller-crimper to terminate the selected crops by measuring cover crop regrowth.
  5. To evaluate the rolled cover crop residue sheet mulch for weed suppression.
  6. To evaluate four different mechanical cover crop termination methods on cover crop regrowth and weed suppression.


Click linked name(s) to expand/collapse or show everyone's info
  • Dale Browne
  • Stafford Crossman


Materials and methods:

Experiment 1:  Evaluation of Three Cover Crops Terminated with a Roller-Crimper On Cover Crop Re-Growth and Weed Development Under Tropical Conditions.

Experiment 1 was the primary experiment conducted within this project. Fields were selected at Sejah Farm to be the experimental location to conduct the 2011-2013 cover crop trials and were previously used for vegetable crop production. The fields selected differed between the 2011/2012 season (year 1) and the 2012/2013 season (year 2). Cover crops were planted during the rainy season to take advantage of seasonal rainfall for cover crop establishment and were terminated at the start of the dry season to coincide with the start of the vegetable crop rotation. Fields selected for the experiment were part of the farm’s primary production fields and differed between years 1 and 2. Farm records indicated that the selected fields were in need of a cover crop rotation and had not been fallowed in 3 to 4 years. Fields were mowed with a rotary deck mower and then tilled with a disc harrow. Prior to planting, the field was disc harrowed for the second time to prepare the seed bed for cover crop planting. The field was divided into 9 sub-fields and each sub-field was randomly assigned to one of three cover crop treatments. Sorghum-sudangrass (Sorghum bicolor x S. sudanense cv. Mega Green, SS) was selected for the cover crop grass species since it is highly adaptable to tropical climates and has been a common cover crop selection among temperate farmers. The legume species consisted of one that represents a cover crop that has climbing/vining stems with a low lignocellulosic content (pliable stems) for which lablab (Lablab purpureus cv. Rongai, LL) was selected and the second leguminous cover crop would be characterized as having erect stems with a high lignocellulosic content for which sunn hemp (Crotalaria juncea cv. IAC-1, SH) was selected. This design resulted in three randomly assigned cover crop treatments with three replications.

Sunn hemp, lablab, and sorghum sudangrass was planted November 1, 2011 (Year 1) and again on October 4, 2012 (Year 2) by broadcast seeding at Sejah Farm. Sorghum sudangrass was seeded at a rate of 40 lbs/acre, SH at 50 lbs/acre, and LL at 65 lbs/acre. After seeding all plots where rolled with a culti-packer to increase seed germination rate. In year 1, all three cover crops exhibited high germination and establishment. In year 2, SS and SH germinated within 7 to 10 days after planting while LL had poor germination, poor establishment, and was negatively affected by heavy army worm herbivory. The LL plots in year 2 were treated as a weedy fallow treatment due to high weed establishment and development in the absence of a suppressive cover crop. In year 2, SS and SH reached vegetative maturity with the plant stand exhibiting greater than 85% flower development at 50 days after planting (DAP). Cover crops were terminated with a roller-crimper 112 days after planting (DAP) in year 1 and 55 DAP in year 2. Differences in plant development and days to termination between years 1 and 2 can be attributed to yearly variation in rainfall and other variable climatic conditions. Prior to termination, cover crop biomass and weed biomass samples were collected from each treatment plot. In year 2, the LL treatments were sampled for weed biomass and then mowed with a rotary deck mower followed by tillage with a disc harrow to simulate conventional tillage. Cover crop plant tissue samples were analysed for nutrient content to assess cover crop nutrient contribution to the system. After all data was collected, cover crop treatments were terminated with the roller-crimper. At 4 and 6 weeks post termination, all treatment plots were assessed for cover crop regrowth and weed development. Data was compiled, analysed, and interpreted for reporting results.

In addition to the primary experiment, two additional research trials were conducted in association with this project.

Experiment 2: Reduced tillage termination of cover crop systems in the tropics 

In the second experiment (year 1) on land farmed by Angel Gonzales, sunn hemp (Crotalaria juncea cv. IAC-1) was established at 2 different planting dates to determine the effects of plant maturity on their response to termination with a roller crimper. Lablab and cowpea (Vigna unguiculata, cv. Iron clay, CP) were established to compare roller-crimper termination effectiveness for spring planted (dry season) and summer terminated cover crops. In addition, several termination methods were tested to compare termination with a roller-crimper to the conventional termination methods of rotary mowing and disc harrowing. The first cover crops planted were SH and CP which were seeded on February 13, 2012 and the second cover crops planted were SH and LL which were seeded on April 26, 2012. The first SH planting represents the mature stand (SH-M) and the second SH planting represents the younger stand (SH-Y).  All cover crops were sampled for biomass yield and weed density prior to cover crop termination which occurred on July 17, 2012. At this termination date, SH-M and CP were terminated 150 days after germination and SH-Y and LL were terminated 76 days after germination. At 4 and 6 weeks post termination, all cover crop plots were assessed for cover crop regrowth and weed development.

In the second experiment during year 2, SH and LL was planted in monoculture in 1 acre fields each. Cover crop establishment, biomass yield, weed biomass yield, and cover crop plant tissue nutrient analysis was determined prior to termination. Both SH and LL were terminated 120 days after planting and each field was then subdivided into four treatment subplots with three replications each. Cover crop termination management treatments consisted of; 1) full incorporation with a disc harrow (three passes), 2) minimum incorporation with a disc harrow (1 pass), 3) mowing with a rotary brush mower (1 pass), and roll down with a roller-crimper (1 pass). Cover crop regrowth and weed biomass was determined at 6, 9, and 12 weeks post-termination. Weed species were separated by weed class and designated either a grass or broadleaf, no sedges were encountered in this trial. Litter bags containing either SH or LL crop residue were placed in their respective fields on day 1 after termination in treatments 1 (buried 2 in. below the soil surface) and 4 (left on the soil surface) to measure decomposition rate and nutrient release over time. Litter bags were collected at 4, 6, and 9 weeks after CC termination and analysed for plant fry matter disappearance and plant chemical properties.

Experiment 3: Trial of sunn hemp as a cover crop planted in April  

The third experimental trial was an on-farm cover crop trial that was conducted at Sun Croix Foods, LLC. SH was planted to serve as a cover crop for soil conservation, soil improvement, and weed control. Sunn hemp was planted on April 11, 2013 with a Great Plains No-Till Drill at a rate of 45 lbs. per acre into lightly disked soil. The SH cover crop fully established and provided the farmer with a cover crop from April, 2013 until October, 2013. Sun hemp biomass and weed biomass was collected prior to cover crop termination on October 4, 2013. The SH cover crop was terminated with the roller-crimper to produce a thick layer of surface sheet mulch which continued to protect the soil for 12 weeks through the rainy 2013 rainy season. During this time SH regrowth and weed development was measured at 3 and 6 weeks after termination.

Research results and discussion:

Experiment 1: Sunn Hemp produced the highest level of CC biomass at 8,091 dry matter (DM) kg/ha which was greater than either the SS or LL at 5,182 or 4,382 DM kg/ha, respectively, in year 1 (p<0.0001). Year 2 resulted in lower CC biomass than in year 1 for both SH and SS at 3,589 and 4,424 DM kg/ha, respectively, (p<0.0001), with no difference in biomass between SH and SS within year 2.  Lablab failed to establish in year 2 from extensive army worm herbivory. Cover crop vegetative biomass yields in year 1 resulted in the contribution of 177 kg/ha nitrogen (N) from SH which was more than SS at 112 kg/ha N or LL at 89 kg/ha N (p<0.05). Due to similar CC biomass yields and plant tissue N content in year 2, there was no difference in N contribution to the farm system between SS and SH. In both years, weed biomass at CC termination was greatest for LL and similarly low for both SH and SS (p<0.05). Sunn hemp responded favourably to termination with a roller-crimper and SH had the lowest level of regrowth.  This was supported by the high amount of both SS and LL re-growth harvested in year 1 and again in year 2 for SS (p<0.0002). However, SH regrowth was greater in year 2 compared to year 1 which could be attributed to differences in SH maturity and lower plant stem lignification. Both SH and SS were effective in suppressing graminaceous, broad leaf, and sedge weed classes following termination where LL was not. Sunn hemp performed well as a tropical cover crop producing high biomass levels and inhibiting weed development. Sorghum sudangrass performed well as a cover crop with excellent weed suppression, but was not effectively terminated with a roller crimper exhibiting a high regrowth potential. In comparison, SH did respond favourably to termination with a roller-crimper by exhibiting a high kill rate that produced surface mulch that inhibited weed development. 

Experiment 2: Year 1 Results indicate that SH terminated at 76 (SH-Y) and 150 (SH-M) days after germination were effectively terminated with the roller-crimper, but were difficult to terminate with the rotary mower or the disc harrow due to the fibrous stem of sunn hemp. Fibre strands wrapped around the rotary mower and the turning disc harrow resulting in mechanical difficulties. The mechanical binding of the equipment was also observed during cutting with a rotary mower/conditioner in a separate experiment. All cover crops established well and resulted in large quantities of biomass that contributed significant amounts of nitrogen to the system. Both CP and LL were not effectively terminated with the roller-crimper and produced large amounts of regrowth. Cow pea and lablab were effectively terminated with a disc harrow.  This has been the accepted cultural method of termination for these two cover crops. Sunn hemp was highly effective at suppressing weeds before termination and after termination with roller-crimper. However, both CP and LL had less weed suppression prior to termination and did not respond well to the roller-crimper as evidenced by high rates of regrowth and weed development. Results of this study indicate that effective cover crop management is highly dependent upon the correct matching of the cover crop species to the proper termination equipment for use in an integrated holistic farm management plan that takes into account soil health and pest management strategies that benefit the agroecosystem.

Differences in results occurred between SH and LL cover crop performance and in their response to the four mechanical termination methods evaluated that included; 1) full incorporation with a disc harrow (3 passes), 2) minimum incorporation with a disc harrow (1 pass), 3) mowing with a rotary brush mower (1 pass), and roll down with a roller-crimper (1 pass). Sunn hemp yielded the highest amount of CC biomass at termination with 6,800 ± 683 kg/ha compared to LL at 3,126 ± 683 (p=0.002). Lablab had greater plant tissue nitrogen (N) content than SH at 2.3% ± 0.1 compared to 1.7 ± 0.1, respectively. However, due to the greater SH biomass, total estimated potentially available N content from cover crop shoot biomass was greater for SH at 117 kg/ha than for LL at 70 kg/ha. 

At 6 weeks after termination, SH had no regrowth within any of the four treatments. Lablab had the greatest measured regrowth from treatment 2 (1,229 kg/ha) and similar regrowth in treatments 1, 3, and 4 (11, 91, and 498 kg/ha, respectively; p≤0.05). At 9 and 12 weeks after termination, SH regrowth was effectively controlled in all termination treatments with the only measurable regrowth occurring in plots terminated with the roller-crimper. In contrast, LL had greater levels of regrowth among all treatments for all three post-termination harvests and termination treatments 1, 3, and 4 resulted in similar LL regrowth for each respective post-termination harvest date. Results indicate that SH had a favourable response to all reduced tillage termination methods tested compared to LL, thus, SH may be better suited for use as a CC in reduced tillage tropical agroecosystems. Sunn hemp controlled grass weeds in treatments 1, 2, and 4 through week 9 and had similar biomass accumulation of grass weeds at week 9 with 0, 0, and 196 ± 127 kg/ha, respectively. At 12 weeks after SH termination, broadleaf and grass weed levels exceeded 1,000 kg/ha in all treatments except for treatment 1 which had the lowest levels at 631 ± 260 kg/ha and 44 ± 260 kg/ha, respectively (p≤0.05).  Therefore, full incorporation with 3 passes with the disc harrow resulted in the most effective termination and weed suppression method for SH. 

Sunn hemp crop residue N content after termination was not influenced by either treatment 1 or 4, but did increase over time from 1 DAT to 28 DAT by 19 percent from 1.7% ± 0.2 to 2.1% ± 0.2 N (p≤0.05), and then returning to 1.7%  N at 42 and 63 DAT. Total N content in LL crop residue was influenced by treatment and time with greater N levels in LL residue from treatment 4 (2.1% to 3.0% ± 0.2 N) compared to treatment 1 (2.1% to 2.5% ± 0.1 N) (p≤0.05). Nitrate-N content in SH surface residue resulting from termination with the roller-crimper increased over time to a high of 348 ppm at 63 DAT.  In comparison, nitrate-N content of SH residue fully incorporated peaked at 180 ppm at 42 DAT and then decreased to 158 ppm at 63 DAT. Lablab surface residue and fully incorporated residue were highest at 42 DAT at 228 and 240 ppm nitrate-N, respectively. From 42 to 63 DAT both surface and fully incorporated LL residue decreased, however, nitrate-N content in surface residue only dropped to 189 ppm while fully incorporated LL residue dropped to 133 ppm. Nitrate-N content of SH surface residue (termination with a roller-crimper) increased over time and provided a slower, delayed conversion of nitrate-N compared to SH residue that was fully incorporated.  Lablab responded in a similar way at 63 DAT where nitrate-N content of surface residue was 30% greater than fully incorporated LL residue.  These findings will allow farmers to more accurately align CC residue nitrate-N availability with peak crop demand and thus, to make improved cover and cash crop management decisions to improve production efficiency. 

Experiment 3: In this on-farm trial, no comparative analysis were conducted and data collected provided supportive information to further strengthen the knowledge base of using SH as a cover crop in the USVI. In addition, the cover crop planted served as a demonstration crop to increase farmer awareness of cover crop use and was viewed by many farmers since the farm in which the SH cover crop was planted on is part of the USVI Department of Agriculture’s community agriculture land that is leased to smallholder farmers for private agriculture production. In this planting, Sunn hemp was planted in April and allowed to establish over the drier months of June and July. The longer growing season resulted in increased SH biomass production with mean shoot biomass of 12,420 kg/ha. Plant tissue nutrient content of SH for N, NO-3, P, and K was 0.021, 0.028, 0.002, and 0.013 percent, respectively. These plant tissue nutrient concentrations in the recorded SH cover crop shoot biomass resulted in estimated potentially available nutrient contents of the surface residue of 257, 342, 20, and 159 kg/ha of N, NO-3, P, and K, respectively. At termination there was 276 kg/ha of broadleaf weeds and 911 kg/ha of grass weeds present. Sunn hemp was effectively terminated with the roller-crimper which is supported by the absence of SH regrowth at either three (0 kg/ha) or six weeks (2 kg/ha) after termination. Weed biomass collected from within the SH surface mulch measured 56 kg/ha of broadleaf weeds and 154 kg/ha of grass weeds. At six weeks after SH termination, grass weed biomass increased to 816 kg/ha, but broadleaf weed biomass decreased to 48 kg/ha. Overall, results from this on-farm trial indicate that SH planted in April can produce substantial quantities of biomass in excess of 12,000 kg/ha and contain high quantities of potentially available nutrients in the cover crop shoot residue that could benefit the cropping system.  

Participation Summary

Educational & Outreach Activities

Participation Summary:

Education/outreach description:

Results from this project have been extensively disseminated to farmers, agricultural professionals, and the scientific community through one-on-one communication, farm visits, webinars, seminars, workshops, field days, and professional scientific conferences. A list of the major organized outreach events at which results from this project have been specifically presented during the active project time period where project results, impacts, and outcomes were disseminated are described below.

Broadcasted Seminar on Cover Crops on Public Radio, July 9, 2013                      Stuart Weiss conducted a one hour radio broadcast seminar on “Cover crops and their importance in vegetable crop rotations”. The broadcast took place on July 9, 2013, was hosted by Clarice Clark from the UVI Cooperative Extension Service, and was part of a community agricultural outreach program called “From the Ground Up”. The program focused on different agricultural topics and was broadcast on public radio to an undetermined number of listeners.   

USDA-NRCS Webinar September 25, 2013 
Results from this project (along with results from similar research initiatives) were presented in a nationally broadcasted webinar on September 25, 2013. The webinar was sponsored by the USDA-NRCS, East National Technology Support Center, and was conducted by Drs. Stuart Weiss and Danielle Treadwell on cover crop technologies. The webinar is titled “Using Cover Crops in Vegetable Production Systems” and was initially viewed by 290 individuals representing 46 states/territories. This webinar has been archived by NRCS and can be viewed by following the link provided:

Cover Crop and Soil Health Workshop for St. Croix and Puerto Rico, April 2014  
Cover Crops and Soil Health Workshop and Field Day – Held April 3 and 4, 2014 at the University of the Virgin Islands, Agricultural Experiment Station (UVI-AES). The event was sponsored by UVI-AES and S-SARE, and organized by Stuart Weiss. This workshop was a collaborative effort with project results presented from two S-SARE funded research initiatives that included results from this On-Farm grant “Promoting Tropical Cover Crop Mulch Systems for Minimum-Till Crop Production in the U.S. Virgin Islands” and the Research and Education Grant “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”.

Collaboration for the event was provided by the University of Florida, Horticultural Sciences Department and the University of Puerto Rico, Agronomy Department.  Co-PIs from the R&E project travelled to the University of the Virgin Islands Albert A. Sheen campus on St. Croix to participate in the event, provide additional technical expertise, and present results from their home institutions. Dr. Danielle Treadwell, Professor of Organic and Sustainable Agriculture from the Horticultural Science Department at the University of Florida and Dr. Elide Valencia, Professor of Agronomy at the University of Puerto Rico, Mayaguez, conducted formal seminars on April 3, 2014 and conducted in-field workshops during the field tour on April 4, 2014. The University of the Virgin Islands Cooperative Extension Service assisted in the event by providing planning and logistical support. Carlos Robles assisted with the event and helped to orchestrate the attendance of two farmers from the St. Thomas farming community to travel to the workshop. Carlos Robles is the Territorial SARE Coordinator and in that capacity provided a published book copy of “Managing Cover Crops Profitably” to all of the farmer attendees. Stafford Crossman assisted in coordinating farmer attendance from the St. Croix farming community. Rudy O’Reily and Julie Wright from the St. Croix, USDA-NRCS department attended and provided sponsorship which included published NRCS educational materials on soil health from NRCS’s “Unlock the Secrets in the Soil” series. There were 45 individuals that attended the two day event that included U.S. Virgin Island farmers (36), government agency representatives (3), and UVI AES/CES professionals (6).  Seminar presentations included;

Soil Health Planning Principles & Cover Crop Management Strategies for the Virgin Islands by Stuart Weiss, Agronomy Program, University of the Virgin Islands.     

Cover Crop Rotations in Vegetable Production Systems by Danielle Treadwell, Horticultural Sciences, University of Florida and Stuart Weiss, Agronomy Program, University of the Virgin Islands.

Cover Crop Rotations for Plantain, Banana, and Corn Production in Puerto Rico by Elide Valencia, Agronomy Department, University of Puerto Rico, Mayaguez, Puerto Rico.

Soil quality, soil aggregation, and soil structure were taught through classroom and field demonstrations.  Different cover crop and vegetable from systems were explored and management principles were conveyed through different field demonstrations. 

On April 8, 2014 a similar seminar and field day was conducted for farmers and agricultural professionals at the University of Puerto Rico, Agricultural Experiment Station at Isabella, Puerto Rico. Dr. Elide Valencia organized the event. Stuart Weiss conducted a seminar and provided program assistance to the field workshop that explored collaborative research projects associated with the SARE Research and Education Grant. There were 30 participants that attended the Isabella, Puerto Rico Cover Crop and Soil Health Workshop. 

A similar workshop and field day is scheduled to be held on Thursday June 4, 2015 at the Suwannee Valley Agricultural Extension Center (SVAEC) in Live Oak, Florida.

Florida Small Farms and Alternative Enterprises Conference, August 1-2, 2014             Stuart Weiss was an invited guest lecturer at the Florida Small Farms and Alternative Enterprises Conference held August 1-2, 2014 in Kissimmee, Florida. Stuart Weiss and Steve Woodruff (USDA-NRCS Agronomist, Greensboro, NC) hosted a two hour workshop series titled “Soil Health in the Subtropics and Tropics”. Weiss presented a two-part lecture as part of the afternoon section; the title of the first seminar was “Crop Management Strategies for the Tropics” and the second lecture was titled “Low-External-Input Sustainable Farming Systems”. The conference session included results, outcomes, and implications from this On-Farm research project and was attended by 73 people.

Conference Proceedings (Weiss was the presenting author for all presentations)                                                                                                                                               Weiss, S.A. 2012. Evaluation of Three Cover Crops and Their Termination with a Roller-Crimper to Produce Residual Surface Sheet Mulch on Cover Crop Re-Growth and Weed Development under Tropical Environmental Conditions. In: International Annual Meetings ASA-CSSA-SSSA; Oct. 21-24, 2012, Cincinnati, OH.

Weiss, S.A. and K.P. Beamer. 2013. Reduced Tillage Termination of Cover Crop Systems in the Tropics. In: International Annual Meetings ASA-CSSA-SSSA; Nov. 3-6, 2013, Tampa, Fl.

Weiss, S.A. and K.P. Beamer. 2014. Evaluation of Three Cover Crops Terminated with a Roller-Crimper on Cover Crop Re-Growth and Weed Development under Tropical Conditions. Proc. 50th Annual Meeting of the Caribbean Food Crops Society, July 6-11, 2014, St. Thomas, United States Virgin Islands.

Treadwell, D.D., S.A. Weiss, E. Valencia, and K.P. Beamer. 2014. Lessons Learned in Conservation Tillage Vegetable Systems in the Sub-Tropics and Tropics. In: International Annual Meetings ASHS; July 26-30, 2014, Orlando, Fl.

Project Outcomes

Project outcomes:

This project has provided numerous quantitative, observational, and experiential results for both scientific advancement and farm improvement. Below is a summarization of the outcomes through individual impact and outcome statements resulting from this grant initiative.

The roller-crimper was successfully designed and built for use with tropical cover crop management systems and put to use in local on-farm research trials.

The successful use of a roller-crimper for the termination of cover crops under tropical conditions is highly dependent upon cover crop species.

Cover crops that have lower lingo-cellulosic pliable stems (stems that do not effectively break or “crimp”), or have low ground based growing points may not be effectively terminated by a roller-crimper alone.

Cover crops can be a valuable management tool in the tropics that require few if any external inputs and SH can be planted throughout the year and achieve full establishment with no supplemental inputs.  

Cover crop regrowth may cause problems when using a roller crimper in tropical or extended warm season environments. 

For vining/twining legumes and grass cover crops, roller-crimper termination may not be viable without herbicide application.

If indeterminate cover crops such as lablab, cowpea, or sorghum sudangrass are to be terminated with a roller-crimper, then an herbicide burn down application prior to termination may be required.

When properly used with the correct cover crop, roller crimper technology is effective at cover crop termination and can result in a thick matt layer of surface mulch that effectively suppresses weeds up to 6 weeks after termination.

Mowing of lablab and cowpea did not provide effective termination when compared to termination with the roller-crimper. 

If using lablab, cowpea, or sorghum sudangrass as a cover crop without an herbicidal burn down, then full incorporation with a disc harrow is required for complete termination to prevent regrowth and to suppress weed development.

Sunn hemp produced large quantities of biomass that effectively reduced weed development prior to termination, and as a result of termination with the roller crimper created a thick surface mulch layer that had little to no regrowth or weed development for 6 weeks following termination.

Sunn Hemp provided the greatest level of weed suppression as a cover crop of the three cover crops evaluated while lablab had the poorest

Sunn hemp stage of maturity contributed to the effectiveness of the cover crop to be terminated with a roller crimper to form a weed suppressive residue barrier. Lignification of the sunn hemp stem at the time of flowering increased termination effectiveness at 110 days after planting compared to less lignified stems at 55 days after planting. An extended growing season for SH when planted in April and terminated in October (176 days) yielded high biomass levels and provided weed suppression prior to and after cover

Lablab had higher plant tissue nitrogen content than sunn hemp, but due to higher biomass production there was greater nitrogen contributed to the farming system through sunn hemp.

Post termination sunn hemp crop residue showed an increase in nitrogen content compared to levels at termination. Surface mulch crop residue of both sunn hemp and lablab exhibited a delayed release of nitrate nitrogen compared to fully incorporated cover crop residue. 

Surface cover crop residue can provide a delayed release of nitrate nitrogen and other nutrients that is more accurately timed with a subsequent vegetable crop’s nutrient demands. Sunn hemp surface sheet mulch has a more pronounced delayed nitrate nitrogen release than lablab surface sheet mulch that may be associated with a higher level of lingo-cellulose.

Economic Analysis

No formal economic analysis was conducted as part of this project and no monetary value was determined for the benefits cover crops can provide to cropping systems and the overall agroecosystem. Ecosystem services provided by cover crops contribute monetary savings and long-term environmental incentives directly to the farmer and indirectly to society and the environment. Cover crops conserve soil from erosion, decrease soil quality and fertility loss, and thus can reduce the reliance on fertilizers and extend soil productivity. Through the suppression of weeds, the use of costly herbicides can be reduced or eliminated providing additional monetary and environmental savings. Many of the benefits associated with cover crops are long-term benefits that span years, decades, and eventually generations of farmers before the full benefit of many of the ecosystem services provided by cover crops are seen. In this sense, conventional economic analysis of long-term cover crop benefits are difficult to apply to short-term studies using contemporary agricultural economic measures. Benefits tend to be long-term while risks are often described as short-term. This also makes it difficult to make a comparative assessment of the risks of cover crops compared to cover crop benefits. The primary risk associated with the use of cover crops is from the potential loss of the crop from which no cover crop benefits would be realized and farmers would have lost the cost of production associated with the cover crop rotation. The loss of a cover crop would be associated with a single year whereas the benefits of cover crops would accrue over the successful years of cover crop use. Further economic analysis associated with both direct and indirect costs and benefits are needed to fully assess the economic sustainability of cover crops within a cropping system and the overall agroecosystem.

Farmer Adoption

In the USVI, approximately 15 small farms have adopted and integrated the use of cover crops into their cropping systems since the initiation of this project. All USVI cover crop workshop farmer participants responded that they are in support of the use of cover crops and would implement the growing of cover crops as part of their farm management plan. There is not a local source to obtain cover crop seed and all cover crop seed must be imported from the United States or internationally. For this reason the cost of cover crop seed is two to three times the cost of seed purchased in the continental USA. Cover crop use requires extensive planning and to plant crop land requires specialized equipment and implements that the majority of USVI farmers do not have access to. These are two of the primary reasons why cover crops are not more readily adopted by small farmers in the USVI. USDA sponsored production and cost-share incentives for cover crop implementation would greatly increase farmer adoption rates.   


Areas needing additional study

There is extensive future work that needs to be conducted regarding the development and use of cover crops in tropical and subtropical cropping systems. Five critical areas in need of immediate research funding are as follows:

  1. To identify and evaluate determinate tropical cover crop ecotypes for use as vegetative covers that produce high biomass levels, develop extensive root systems, sequester and/or biologically fix high concentrations of soil nutrients, are disease and pest tolerant, and drought resistant.
  2. Breeding of specialized plant cultivars specifically for self-terminating, determinate lines that do not require termination through full-tillage soil incorporation or chemical burn down for use in conservation tillage systems that can be effectively terminated with a roller crimper at maturity with no regrowth potential.
  3. Determine optimal cover crop termination time for use with minimum till roller-crimper technologies based on plant lingo-cellulosic content and plant physiological maturity based upon photoperiod sensitivity when grown in the tropics.
  4. To evaluate the multipurpose crops Crotalaria juncea L.), sesame (Sesamum indicum Linn.), and sunflower (Helianthus annus L.) as dual purpose cover crops and as supplemental pollen and nectar sources to improve honey bee nutrition and hive productivity during seasonal periods of low pollen and nectar availability.
  5. To evaluate the short-term and long-term ecosystem services of cover crop legacy effects in integrated agricultural cropping systems that includes their use in tropical vegetable production systems. Specific ecosystem services in need of further research are the effects of cover crops in tropical agroecosystems on; erosion control, soil conservation, soil quality, soil microbial communities, soil moisture, carbon sequestration, pest suppression, plant and soil pathogens, mixed crop-livestock systems, pest and beneficial insect populations, biodiversity, and environmental protection.

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.