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Beneficial Uses of Compost in Florida Vegetable Crops - Page 4
Crop injury has been linked to use of poor-quality compost, such as that from early stages of the composting process. The type and degree of plant injury is directly related to compost maturity or stability. Maturity is the degree to which it is free of phytotoxic substances that can cause delayed seed germination, or seedling and plant death; stability is the degree to which compost consumes N and O2 in significant quantities to support biological activity, and generates heat, carbon dioxide (CO2), and water vapor that can cause plant stunting and yellowing of leaves. Plant stunting has often been attributed to high C:N ration of the organic material
before humification, and plant injury from exposure to phytotoxic compounds such as volatile fatty acids and ammonia. Phyototoxin identification in compost extracts from fresh and 5-month-old municiple solid waste (MSW) material showed that fresh compost contained acetic, propionic, isobutyric, and isovaleric acids in the largest concentrations. Acetic acid at 300 ppm concentration inhibited growth of cress seed.
In Florida, soil application of unstable compost consistently resulted in "N-immobilization," where available forms of inorganic N were converted to unavailable organic N followed by growth inhibition of vegetable crops such as beans, corn, peppers, tomatoes and squash. When immature compost is applied and a crop is planted immediately, growth inhibition and stunting may by visible for 40 to 60 days
(Figure 1). When using compost with C:N ratios higher than 25 or 30, N fertilizer should be applied, or planting delayed for 6 to 10 weeks to allow the compost to stabilize in the soil.
Research on vegetable compost utilization in Florida has established several potential applications: soil amendments, soilborne disease suppression, biological weed control, alternative to polyethylene mulch, and as a transplant media.
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