Tropical Island Forages May Be Good Fit as Summer Cover Crops

ST. CROIX, Virgin Islands – When you live on an island perpetually faced with high import costs and limited resources, producing food sustainably is more of a way of life than a choice.

But even then, sustainable ag production for growers in the U.S. Virgin Islands doesn’t come without additional crop production challenges when the tropical climate fuels an endless onslaught of weeds, pests, diseases, and low soil fertility.

“We have endless summers here. We get no seasonal breaks from weeds or insects, and the soil microbial environment is extremely active which rapidly decreases soil organic matter in tilled soils,” said University of Virgin Islands Agricultural Experiment Station agro-ecologist Stuart Weiss. “So anything that we can do to help our farmers sustainably manage these burdens and become more successful is important to us.”

With a $14,957 Southern Sustainable Agriculture Research and Education (SARE) On-Farm Research Grant, Weiss is putting his own spin on sustainable agriculture by taking tropical crops traditionally grown as forages and using them as cover crops in surface mulching systems in various vegetable crop rotations.

The primary goals, said Weiss, are to determine if the cover crops -- nearly all of them legumes -- can be incorporated into minimum tillage production systems to minimize soil nutrient losses, recycle soil nutrients, add nitrogen to the soil through biological nitrogen fixation, increase or maintain soil organic matter, reduce moisture loss, and suppress weeds.

“Managing crops conventionally is difficult because of the high costs of imported fertilizers, implements, and other production inputs.  Large scale conventional crop production is just out of reach for most of our farmers,” said Weiss.

In the U.S. Virgin Islands, 87 percent of all farms have less than $10,000 in total farm sales per year and 40 percent of all farms is three acres or less, so sustainability is a critical component to the island’s agricultural system.

“At the same time, gaining access to organic fertilizers like cow manure and chicken litter is difficult, simply because we don’t have conventional livestock confinement operations to support such manure production and, again, imports are costly,” said Weiss. “So we have to use existing on-farm resources and alternative inputs that we have here on the island.”

In the two-year study (OS10-062), “Promoting Tropical Cover Crop Mulch Systems for Minimum Till Crop Production in the U.S. Virgin Islands,” Weiss will study leguminous covers sunn hemp, lab lab, butterfly pea, and pigeon pea; and grass covers sorghum-sudan and pearl millet in vegetable crop rotations with popular crops such as peppers, eggplant, tomato, cucumber and okra.

“The research will test the response of different mechanically killed tropical cover crops with a roller crimper for their continued use as organic sheet mulch in minimum-till crop production systems,” said Weiss. “Expected benefits include the creation of nutrient-rich mulch that will last until the harvest of the following crop, and thereby, shade the soil and reduce water loss from evaporation, reduce weed germination and development, and serve as an organic soil amendment.”

The research, said Weiss, is not only beneficial to farmers on the island, but may also prove useful to farmers stateside looking for alternative cover crops.

“Lesser-known tropical forage crops, like butterfly pea, pigeon pea, or lab lab, shouldn’t be dismissed,” said Weiss. “They have potential use in warm climates as cover crops that could be a good fit for summer rotations.”

The crop selections being tested could give farmers alternative cover crop choices that have heat and pest tolerance, and can contribute nitrogen to the soil through biological fixation, said Weiss. 

“The different management practices we are evaluating will give farmers the tools needed to get the most out of their cover crops even in harsh environments,” he said.

The On-Farm Research Grants program is one of S-SARE’s seven grant opportunities. It’s tailored for ag professionals who work directly with farmers and ranchers to find sustainable solutions to ag production issues.

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Published by the Southern Region of the Sustainable Agriculture Research and Education (SARE) program. Funded by the USDA National Institute of Food and Agriculture (NIFA), Southern SARE operates under cooperative agreements with the University of Georgia, Fort Valley State University, and the Kerr Center for Sustainable Agriculture to offer competitive grants to advance sustainable agriculture in America's Southern region.