Soil and Water Science Extension Program
The Soil and Water Science extension program at the Tropical Research and Education Center (TREC) focuses on demonstrating improved fertilizermanagement strategies through on-farm trials, grower and county extension workshops, and seek grower adoption of these practices; educating on using soil organic amendments for crop production and introduce new cover crops to growers through field demonstrations; and training on water quality concepts, sampling and chemical analysis.
Water quality issues are of considerable concern because of the excessively porous, oolitic limestone soils that overlay the Biscayne Aquifer, and through which it flows. The aquifer underlies the Everglades Protection Area and Miami-Dade County and empties into Biscayne and Florida Bays. These areas and bays represent large natural resources for water, recreation, and habitat for native flora and fauna, which must be protected from pollution.
In addition, groundwater is the primary source of drinking water for Miami-Dade County residents. Agrichemicals (P and pesticides) at elevated concentrations have been measured in aquatic systems of south Florida indicating a need to pro-actively reduce agrochemical leaching through innovative management.
In addition to agriculturally related natural resource initiatives, urban sources of pollution (residential and city-urban) also need to be addressed. Our water quality training program focuses on basic concepts of water chemistry and hydrology, and provides practical training related to water sampling and analysis, instrumentation, water quality data analysis, evaluation and reporting.
The predominant agricultural soils in this area are typified by Krome very gravelly loam, which is characterized by an alkaline pH, very gravelly texture, low water holding capacity, but rapid permeability. These unique soil conditions create universal problems for crop production in this area, such as low use efficiency of fertilizers, micronutrient deficiencies, and potential leaching of nutrients into groundwater. Most agriculture soil samples have high plant available and total P, and that the addition of P fertilizer did not improve crop yield and quality.
Over-fertilization leads to unnecessarily high production costs, may decrease yield and quality, and poses a risk to the environment. Moreover, excessive rates of phosphorus may induce iron chlorosis or other micronutrient deficiencies of crops grown on rocky soils. On the other hand, micronutrient deficiencies are common problems for most crops in the area due to high soil pH, inadequate fertilizer applications, or use of improper fertilizer formulas.
Soil Organic Amendments
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.
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, 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.