Several hundred commercial crops and diverse native plant species grow on calcareous gravelly or marl soils of the south Florida agricultural and Everglades ecosystems. At the outset information on these calcareous soils was scant, but in last several years my research group determined their physical properties (hydraulic conductivity, etc.), chemical properties (carbon forms, phosphorus sorption, etc.), biological properties (microbial biomass, etc.), and mineralogical properties. These findings were used to develop our extension program, teach students, and support others in conducting agricultural and ecological research in south Florida.
Soil Phosphorus Chemistry
High phosphorus concentrations in the run-off from farmlands facilitate the displacement of native vegetation by undesirable vegetation. Everglades restoration, as well as sustainable crop production, requires major reductions of phosphorous in runoff, and this requires in-depth knowledge of phosphorus biogeochemistry in soils. We conducted a series of laboratory, greenhouse and field experiments on phosphorus chemistry and phosphorus fertilizer use efficiency in calcareous gravelly and marl soils. We found that most agricultural soils have high concentrations of phosphorus in forms likely to move into surface and groundwater even under calcareous conditions, and that additional applications of phosphorus fertilizer did not increase phosphorus availability and crop yield. We developed a simple one-point isotherm method to predict saturation and leaching potential of phosphorus in calcareous soils. We found apatite formed in calcareous soils farmed for many years.
Everglades Soil and Water Quality
The invasion of the southern Everglades (Hole-in-the-Donut (HID) area) by Brazilian pepper was caused by rock plowing the marl soils to permit intensive crop production. We investigated the role of soil conditions in this invasion, and evaluated physical, chemical and biological changes in marl soils newly formed after the removal of the rock-plowed soil. We made environmental assessments of soil mounds created from the removed soil. We are also collaborating with soil scientists and ecologists in the park to evaluate water quality. Our research has provided a fundamental understanding relevant to restoration of this fragile ecosystem.
Water Quality In Miccosukee Indian Reservation
The Miccosukee Tribe of Indians of Florida finds that excessive nutrients (including total phosphorus) constitute one of the most severe water quality problems threatening the Everglades Ecosystem. The Tribe is trying to limit the introduction of nutrients from anthropogenic sources into waters of the Tribe. We are establishing flow-proportional water quality monitoring stations and collect data of water quality parameters (pH, EC, DO, ortho-P, total P).
Soil and hydrological evaluation of Loxahatchee River Watershed
The Loxahatchee River is generally referred to as the "last free flowing river in southeast Florida". The Loxahatchee River watershed drains an area of approximately 200 square miles. The overall goal of this project is to assess changes in soil characteristics within the floodplains of the Loxahatchee River in order to understand the relationship between surface, groundwater and soil interactions on floodplain vegetation; and to determine the duration of inundation and moisture in the area.
Nutrient Management for Tropical Fruits and Vegetables
Poor soil conditions create universal problems for crop production in south area, such as low use efficiency of fertilizers, microelement deficiencies, and potential leaching of nutrients into groundwater. An estimated 60% of vegetable acreage in Dade County receives fertilizer rates that exceed UF recommendations. Similar situations exist for tropical fruit and ornamental crops. Over-fertilization leads to unnecessarily high production costs, may decrease yield and quality, and poses a risk to the environment. 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. Moreover, excessive rates of phosphorus may induce iron chlorosis or other micronutrient deficiencies of crops grown on rocky soils.
Cover crops are an integral part of vegetable production practices in south Florida. We introduced a legume cover crop, sunn hemp (Crotalaria juncea L.), which produces up to 12,000 kg dry matter and fixes up to 300 kg nitrogen per ha. We evaluated mineralization rates of cover crops and effects of cover crop residues on soil organic carbon, soil microbial biomass, soil enzyme activity, and water holding capacity. We showed that tomato planted into sunn hemp plots produced more marketable and extra large fruit. Our findings provide fundamental information on enhancing the sustainability of agriculture through use of sunn hemp and other cover crops. We currently are conducting experiments using cover crops to improve soil quality and crop production in Peru.
Soil Organic Amendments
Several projects are conducting to evaluate the effects of soil amendments (compost, biosolids, fly ash, zeolite) on crop production, soil fertility and water quality. We developed a method to quantify organic carbon in organic waste amended calcareous soils that overcomes interference of carbonate in calcareous soils. We modified fractionation methods for organic carbon and metals, to be better suited for calcareous soils. We also developed management practices to utilize biosolids or composts, which significantly increased soil organic carbon, increased soil nutrient availability and increased crop yields, but avoided trace metal accumulation in soils and nutrient leaching into groundwater. Our studies also indicated that incorporation of coal ash into biosolids and yard waste composts significantly improves their quality. Such use may be made of the 80 million tons of coal ash from power plants national wide, together with the 3 million tons of yard waste produced annually in Florida alone.