Best management practice (BMP) development and implementation in southwest Florida is relatively recent (<10 yrs). Therefore, growers need field data validating the effects of BMPs on production and profits under conditions unique to this area of the state. Likewise, regulators with federal and state organizations (e.g. U.S. EPA, Florida Department of Environmental Regulation, Florida Department of Agriculture and Consumer Services and South Florida Water Management District) need solid science on which to evaluate the effectiveness of present BMPs and to determine the need for additional BMPs to be implemented in the future. Focus crops in the southwest Florida area are citrus, sugarcane, and vegetables.
To address these goals, two 5-year research projects titled “Improved nutrition of citrus, sugarcane, and vegetable crops grown on sandy soils in southwest Florida” (FLA-IMM-004718) and “Modeling of water and nutrient uptake, and soil nutrient transformations and transport in Florida sandy soils” (FLA-IMM-004719) were developed as part of the Florida Agricultural Experiment Station Current Research and Information System (CRIS). The following are the objectives and status of these CRIS projects.
The sandy soils of south Florida have poor water and nutrient retention capacities. Therefore, adequate supplies of irrigation water and fertilizer nutrients are required for optimal production. The impact of N and P movement and transformation at a field scale on water quality is of primary concern in the region. Best management practices addressing water quality and water management (water quantity) issues on a commodity or watershed basis are being implemented. A key aspect of these BMPs is to address concerns related to contamination of some surface and aquifer water resources by agricultural nutrients. Studies to assess nutrient application rates and timing, irrigation management, and use of controlled released fertilizers have been implemented to increase nutrient use efficiency and minimize nutrient loss to the environment. Soil testing and irrigation/fertigation management BMPs to correspond with crop nutrient demand and thus, to reduce nutrient loading through reduced nutrient leaching rates have also been implemented. Local growers have become increasingly interested in information on agronomic crops for bio-fuel production. Water management districts and FDACS are also interested in these questions. Two preliminary research projects on water consumption and water quality impacts of these crops was began by an interdisciplinary team of scientists from SWFREC and EREC.
The collection of data from long-term, field-level citrus, vegetable and sugarcane is required to establish nutrient recommendation for BMPs. The validation of nutrient BMPs requires the evaluation of: 1) soil nutrient movement with irrigation and rain water, 2) nutrient transformation rates, 3) crop nutrient availability and 4) crop growth and yield. Improved fertilizer nutrient use efficiency and the resulting fertilizer rate reductions can decrease surface water quality impacts from agricultural production in the ecologically sensitive south Florida environment. Reductions of 10% or more in current commercial N rates have been established for both tomato and sugarcane and verification using grower cooperative demonstrations. The use of controlled-release fertilizers has resulted in reduced N applications of 25% to 35%. Increased fertilizer use efficiencies have been supported by field studies on nutrient movement within plastic mulched beds with fluctuations in soil water content to determine the potential impact of irrigation mismanagement or leaching rain events on leaching of nutrient below the root zone. An improved soil test P index on high pH and Ca concentration soils in south Florida can lead to improved use of P and improved surface water quality: a 25% increase in growth and yield of green beans has been documented on soil with P indices of high and very high.
Research on the impact of water uptake on tree growth and production has led to the development of two irrigation management models. These models were validated using data collected during a 3-year study with 6 cooperators, 3 on ridge soils and 3 on flatwood soils. The effort and models are further described below in sections 12B and 23. The effect of irrigation frequency and quantity on citrus production is being evaluated using daily and seasonally adjusted irrigation schedules. Water use on both ridge and flatwood soils is being evaluated to determine the effect of density, tree canopy volume and soil series on water consumption and soil water status. Improved nutrient use efficiency and reduced water consumption are expected outcomes of this study. An investigation of intensive irrigation and nutrient management of young citrus trees has resulted in 20% increase in growth in the first year.