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

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

Summary

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/yr gross annual income) with 63% of farms totaling 9 acres or less and 81% of farms totaling 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 6 months.  Both surface and subsurface ground water is severely limited and farmers rely strictly upon precipitation for agronomic production and the use of water conservation practices such as micro irrigation from harvested rainwater stored in tanks/ponds or pumped from shallow wells for fruit and vegetable production.  Therefore, the supply of sufficient soil-moisture levels for crop production during the dry season is often a limiting factor for crop production in the USVI.

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. Soil fertility and pest management create unique challenges to USVI farmers in that imported fertilizers and pesticides are 2-to 3-times the cost of inputs in the continental USA and they 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 and are often not available at all.  Therefore, low-external-input agriculture must utilize alternative production methods which will increase soil fertility and reduce pest incidence by implementing green manure cover crops, sheet composting, crop rotation, and conservation tillage technologies.    

  Cover crop benefits to agroecological systems 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, especially when conventional soil tillage methods are practiced.  This is due to a 12 month hot and humid climate and the lack of seasonal changes that result 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.  Minimum- 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. Roller crimper implementation that mechanically kill tropical cover crops by “rolling” and “crimping” plant material into surface residue results in an organic mulch 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 intensive tillage practices that fully incorporate cover crops.  This management technique combines sustainable farming techniques of cover crops, green manure, organic mulch, and conservation tillage for sustainable low-external-input agriculture. 

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 roller crimper termination and their vegetative regrowth potential has not been documented.  This project will provide crucial baseline information on the potential of roller-crimper technology for its applied use in tropical/subtropical agroecosystems to reduce tillage, increase soil quality, and provide a number of different ecosystem services to increase overall farm sustainability.

Objectives/Performance Targets

This Southern SARE On-Farm grant will provide the initial means to evaluate several promising tropical cover crops, evaluate and demonstrate a roller-crimper for tropical cover crop technology, quantify the cover crop species response to termination with a roller-crimper, and measure the effectiveness of the roller crimper to suppress cover crop regrowth and weed development.   

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 no-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 evaluate and compare three 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.   
2. To measure the selected cover crops ability to suppress weeds prior to termination.
3. To determine the effectiveness of using a roller-crimper to terminate the selected crops by measuring cover crop regrowth.
4. To evaluate the rolled cover crop residue sheet mulch for weed suppression.

Accomplishments/Milestones

Fabrication of the Roller-Crimper – The first step in this project was to successfully fabricate a full scale operational roller crimper that we custom designed by incorporating ideas and designs based on several previously constructed roller-crimper prototypes using locally available recycled materials. Design of the roller-crimper was primarily based upon roller-crimper technology developed by the Rhodale Institute and other roller-crimper models as featured on Rhodale’s website at http://www.newfarm.org/depts/notill/roller_gallery/ . For the drum construction of the roller-crimper, a 6’ft x 2’ft (LxW) of 3/8”in (wall thickness) steel pipe was end capped with recycled 24”in turning plow discs that had operational hubs. The hub shafts were welded to a fabricated tool bar with a 3 point hitch. The drum was then fitted with 3”in flat bar steel welded at 6”in spacing to the drum in a diamond pattern to alleviate vibration and to increase crimping pressure. Fill and drain plugs were then added to the drum for the addition of water to increase implement weight. Our roller-crimper was completed in December 2011 after having to correct several welding errors and make several slight modifications to the original design.

Establishing the On-Farm Research Project – St. Croix has a bimodal rainfall pattern that consists of a well-defined rainy and dry season. The optimal time for cover crop establishment is during the height of the rainy season which covers the months of August, September, October and November. Timing of cover crop planting to the seasonally high rainfall months has many benefits which include having a cover crop in place to reduce soil erosion, capture more surface water into the soil strata, and have the cover crop rotation during a period of the year when there is an increased level of weed and insect pest pressure. St. Croix has limited surface and ground water availability which prevents large scale irrigation practices and therefore the establishment of cover crops during the extended dry season is limited and must be carefully timed with intermittent rainfall events.

In September of 2011, cooperative work began with Dale and Yvette Brown on Sejah Farm (http://sejahfarm.com). “Sejah Farm is situated in what we call the ‘farm belt’ of the island. Its fifteen acres of farm land, consists of eleven acres that are used as grazing for sheep and goats; three acres that are used for vegetable crop production; and, three quarter acres used for poultry production. We raise Boer Goats and Boer Goats crosses for sale, local fresh meat, and vegetables for local and off-island demands” (Dale Brown). Production fields were identified that were in need of rotation and that would benefit the most from a cover crop rotation. Three fields were identified that ranged in size from 0.25 acres to 0.75 acres and these three fields were prepared for planting using a minimum till ripper, followed by a disk harrow. Each field was then subdivided into three equal plots where each field represented an experimental replication and each subplot represented a cover crop treatment. Three cover crops were strategically selected in order to have a well-represented morphological range of cover crop plant species. For the initial testing it was determined that a common grass cover crop species and that two legume species be evaluated. Sorghum-sudan grass (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 would consist of one that represents a cover crop that has stems with a low lignocellulosic content (pliable stems) for which lab lab (Dolichos lab lab cv. Rongai, LL) was selected and the second leguminous cover crop would be characterized as having stems with a high lignocellulosic content for which sunn hemp (Crotalaria juncea cv. IAC-1, SH) was selected. One of the primary objectives of this project is to evaluate how cover crops respond to mechanical termination with a roller-crimper on low external input farms without the use of an herbicide burn down and no seasonal kill (Winter or Summer). Therefore, it was important to collect data on a broad plant morphological basis due to the lack of knowledge in this subject area.

On October 31, 2011 SS, SH, and LL was planted at Sejah Farm by broadcast seeding. Sorghum sudan was seeded at a rate of 40 lbs./acre, sunn hemp at 50 lbs./acre, and lab lab at 65 lbs./acre. After seeding, all plots where rolled with a culti-packer to increase seed germination rate.

All cover crops germinated within 7 to 10 days after planting and cover crops were allowed to fully establish for a period of 100 days after planting or 90 days after germination. At 90 days after full germination and at least a minimum of 75% flower development, all cover crops were sampled for cover crop biomass yield and weed development in the cover crop understory was assessed. Cover crop plant tissue samples were analyzed for nutrient content to assess cover crop nutrient contribution to the system. After data was collected all cover crops were terminated with the roller-crimper. At 4 and 6 weeks post termination, all cover crop plots were assessed for cover crop regrowth and weed development.

In a separate experiment 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. Lab lab 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 planter 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.

Impacts and Contributions/Outcomes

Clear impacts and outcomes resulted from the initial on-farm research at Sejah Farm. All three cover crops established well and contributed a significant amount of biomass and nitrogen to the agricultural system prior to termination. Sunn hemp (SH) produced the greatest amount of biomass at 8,000 kg/ha which contributed 177 kg/ha of nitrogen to the system. Sunn hemp had near complete suppression of weeds (

In the second experiment SH-Y and the SH-M had a positive response when terminated with the roller crimper, but were difficult to terminate with either the mower or the disc harrow due to the fibrous stem of sunn hemp. Fiber 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 amounts 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 lab lab 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 pre and post termination with a 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 entire agroecosystem.

Individual Outcome Statements:

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.

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

The proper selection of cover crop varieties that have determinant plant characteristics such as sun flower or sesame may improve termination response.

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 lab lab and cowpea did not provide effective termination over termination with the roller crimper.

If using lab lab or cowpea 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 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.

Professional Contribution:

American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America National Conference Abstract Submission and Oral Presentation.

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. University of the Virgin Islands, Kingshill, US Virgin Islands.

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.

Stuart A. Weiss, Agriculture Experiment Station – Agronomy Program, University of the Virgin Islands, St. Croix, AA

Tropical smallholder farmers operating under low-external-input conditions rely upon non-intensive on-farm inputs such as cover crops (CC) to provide ecological and economical means for the management of soil quality, soil fertility, and pest management. Roller-crimper technologies for the termination of CC to produce residue based surface sheet mulch were developed in temperate climates where environmental seasonal changes impede CC re-growth.   Information on the response of CC to termination with a roller-crimper and resulting weed suppression is limited or non-existent for tropical environments. The objective of this project is to; 1) evaluate three CC under tropical environmental conditions produced with zero external inputs, 2) to determine CC residue re-growth levels, and 3) to evaluate weed suppression capabilities after termination with a roller-crimper to produce surface sheet mulch. Sunn hemp (SH; Crotalaria juncea (L.) cv IAC-1), lablab (LL; Lablab purpureus (L.), cv Rongai), and sorghum sudan (SS; Sorghum bicolor x S. sudanense L. cv Mega Green) were planted November 1, 2011 by broadcast seeding. The experimental design was a RCBD with 3 replications. Cover crops were terminated with a roller-crimper 112 days after planting. Plant data was collected on CC and weed biomass production prior to termination; and CC residue height, weed biomass, and CC re-growth biomass were determined 30 days after termination. Sunn Hemp produced the highest level of CC biomass at 8,091 dry matter (DM) kg/ha which was significantly greater than either the SS or LL at 5,182 DM kg/ha and 4,382 DM kg/ha, respectively (p<0.0001). Cover crop vegetative biomass yields 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). No difference in phosphorus or potassium contribution was seen between the three CC evaluated.   Weed biomass at CC termination was greatest for LL with 264 DM kg/ha graminaceous weeds (GW) and 218 DM kg/ha broad leaf weeds (BLW) compared to SS with 18 DM kg/ha GW and 31 DM kg/ha BLW or SH with

Two minor workshops toured the farm projects to showcase tropical cover crops to local farmers. Two farmers adopted cover crop practices as a result of this year’s cover crop work.

• ASA Presentation 2012

Collaborators: