Submitted to: Renewable Agriculture and Food Systems
Publication Type: Peer reviewed journal
Publication Acceptance Date: 3/6/2006
Publication Date: 5/7/2006
Citation: Wang, Q.R., Li, Y., Klassen, W., Handoo, Z.A. 2006. Influence of cover crops and soil amendments on okra (abelmoschus esculentus l.) production and soil nematodes. Renewable Agriculture and Food Systems. 21(3):1-13. Interpretive Summary: Plant-parasitic nematodes are microscopic worms that live in the soil and cause an estimated ten-billion-dollar crop loss in the United States each year. These losses will increase because the most widely used chemical pesticide for killing nematodes will soon be prohibited. One approach to solving the problem of designing new, safe means of controlling nematodes is through the use of cover crops or soil amendments. Cover crops are plants that nematodes will not infect; these plants can be grown to potentially reduce nematode numbers in soil. Soil amendments are organic materials that can improve soil and plant health. In the present study, ARS and University of Florida scientists evaluated two different cover crops (sunn hemp and sorghum sudangrass) and several organic soil amendments in field and pot experiments to determine if they could reduce population levels of the root-knot nematode, the most economically important nematode infecting vegetables in the United States. The scientists discovered that each cover crop, especially sunn hemp, stimulated okra yield and suppressed root-knot nematode levels. In addition, the combined use of cover crops and certain organic amendments improved okra production further. These results are significant because they indicate that these cover crops alone or with organic amendments offer promise as replacements for chemical nematicides in some okra production systems. This research will be used by scientists developing new methods for safely controlling nematode-induced crop losses.
Technical Abstract: A pot experiment to determine the effects of summer cover crops and soil amendments on okra yield and population densities of various soil nematode taxa was conducted in two consecutive growing seasons in a subtropical region. Two cover crops, sunn hemp (Crotalaria juncea) and sorghum sudangrass (Sorghum bicolor x S. bicolor var. sudanense), were grown and returned to the soil with fallow as a control. As soon as these cover crops were terminated by cutting the stems at ground level, they were incorporated into soil together with one of the organic amendments. The latter were biosolids, N-Viro Soil, coal ash, co-compost (3:7 mixture of biosolids to yard wastes), and yard waste compost. Other treatments were a control (no additional amendment), fumigation with MC-33 (a mixture of 33% methyl bromide and 67% chloropicrin) and cover crop removal, i.e. when the cover crop reached the stage for termination its shoots and roots were removed. A nematode susceptible vegetable crop, okra (Abelmoschus esculentus L.), was evaluated in all treatments. Among organic amendments, the application of biosolids produced the highest okra yield and biomass, and greatly suppressed the root-knot nematode, Meloidogyne incognita, populations in the soil. Sunn hemp was superior to sorghum sudangrass in improving okra production and in suppressing root-knot nematodes. The results indicate that growing sunn hemp as a cover crop and applying certain organic amendments can improve okra production and suppress root-knot nematodes. Such combined use of cover crops and organic amendments has significant potential for application in organic farming and sustainable agriculture systems.