Sandy and gravelly soils in south Florida are low in organic matter, have low water and nutrient holding capacities, and high nutrient leaching potentials. Using organic materials as soil amendments on Florida soils usually improves soil fertility and generally (but not always) increases crop yields. Soil organic amendments are usually in the form of cover crops, biosolids, or municipal solid waste composts.
Composts
Various research projects have demonstrated that biosolids or composts can serve as soil amendments to increase soil organic matter, improve soil microbial activity, provide nutrients and ultimately improve plant growth and yield. However, high variability in the quality of operations between and within compost production facilities leads to unpredictable compost quality. Often, the use of immature composts can result in plant phytotoxicity. The introduction of viable weed seeds and high salt concentrations are also potential hazards of compost utilization in cropping systems. These conditions have created a need to inform producers about proper management practices for the use of organic wastes for crop production.
Cover Crops
Cover crops, commonly referred to as green manures, are also important soil organic amendments. Cover crops are used to improve soil physical properties, increase soil organic carbon, conserve soil water, reduce surface runoff, and recycle nutrients during the heavy summer rains. Legume cover crops can contribute as much as 300 lb N /ac and non-legume cover crops can contribute ca. 100 lb N /ac to the following crops. However, few growers have adjusted their fertilizer programs to consider the nutrient input from cover crops.
A wide variety of plants are used as cover crops in south Florida. Legumes like cowpea contribute more nitrogen by fixing nitrogen (N) to the soil than non-legumes like sorghum-sudangrass due to symbiotic N fixation. This program is introducing various cover crops to growers, and helping them to account for the nutrient contributions in the design of their fertilizer management programs.
