Dr. Samira Daroub- Associate Professor, P.I.
	Dr. Orlando Diaz- Research Associate
	Dr. Timothy Lang- Research Associate
	Irina Ognevich- Chemist
	Viviana Nadal- Sr. Chemist
	Theresa Sanford- Sr. Lab Technician
Research conducted in this lab

Background and Objectives

The University of Florida/Institute of Food and Agricultural Sciences (UF/IFAS) phosphorus (P) concentration and load reduction agricultural best management practice (BMP) research and education program began in 1986.  At that time, it was alleged that P in agricultural drainage water leaving farms in the EAA was negatively impacting surrounding ecosystems.  Furthermore, fertilizer applied to sugarcane crops was believed by many to be the primary source of the elevated P concentrations and loads.  It was hypothesized that agricultural BMPs could contribute significantly to alleviating the problem.  Prior to developing BMPs, it was necessary to provide a working definition of a BMP which would properly constrain the breadth of potential practices.  That definition, pertinent to the EAA is:  An alternative management practice that is technically feasible, economically viable, socially acceptable, and scientifically sound, that when implemented, will lead to reduced P concentrations and loads leaving farms in the EAA, while not threatening the viability of the agricultural industry.

In 1986, the UF/IFAS entered into a research contract with the South Florida Water Management District (SFWMD), the Florida Sugar Cane League, the Florida Sugar Cane Growers’ Cooperative, the United States Sugar Corporation, the Florida Crystals Corporation, the Florida Fruit and Vegetable Association, and Roth Farms, Incorporated.  The objective of the research contract was to determine what agricultural practices could be changed to reduce the P concentrations and loads leaving EAA farms.  The primary foci of the study were to determine the effects of fertilizer rates and application methods and water management practices on drainage water P loads and concentrations.  Potential BMPs were screened using large field plots.

Results of this initial work showed that sugarcane fertilizer related practices did not lead directly to short-term P concentration and load increases since application amounts are low.  Vegetable crop fertilization practices, however, were found to be capable of causing short-term P spikes given certain hydrologic and cultivation conditions.  Banding fertilizer for vegetable crops at reduced rates, and using proper fertilizer handling and application methods for all crops, could lessen the occurrences of fertilizer related short-term increases in P concentrations and loads.  The study also showed that water management practices greatly affected both P concentrations and loads.  Obviously, pumping less water off farms yielded large and immediate reductions in P loads.  However, drainage rates and uniformity could also greatly affect P loads and concentrations positively or negatively.  It was, therefore, determined that a combination of improved drainage uniformity and a reduction in drainage pumping could yield significant reductions in P concentrations and loads for all crops.

In addition to the above, it was determined that sugarcane land yielded P concentrations and loads that were equal to, or lower than, fallow land that was allowed to flood and drain.  Also, in spite of the effects of the higher fertilization rates, and the more demanding water management requirements of vegetable crops, vegetables could be grown in the EAA without greatly affecting P concentrations and loads.  To accomplish this, the growers were advised to block farms into hydraulically isolated units and to rotate crops accordingly.  By doing so, vegetable field drainage water would not directly enter the farm drainage stream, but rather would be diverted to sugarcane blocks for retention or detention.  Additionally, it was determined that growing rice in rotation with vegetables, which requires no additional P fertilizer, yielded a major export of P from the EAA in grain and held nutrients in plant matter which could then be reincorporated into the soil.  It was cautioned, however, that drain down of the rice floodwater be accomplished in a manner such that it did not directly enter the drainage stream.  Allowing the floodwater to subside naturally leaves residual nutrients in the field for use by the succeeding crops.  Additional drainage required to lower water table levels should be discharged to sugarcane field blocks, keeping the nutrient enriched water from directly entering the farm drainage stream.  This practice was extrapolated to pertain to all floodwaters, regardless of whether they originated from rain, or purposeful flooding of fallow fields.

The initial study lead to the development of a table of BMPs for reducing P concentrations and loads in the EAA (Table 1).  Using the results of the study, and best professional judgement, expected reductions in P loading were attached to each BMP in the table.  It was hypothesized that P load reductions ranging from 20 to 60% could be realized for farms in the EAA and for the basin as a whole.  The BMPs from Table 1, and others suggested by industry and the SFWMD, were selected by the SFWMD for inclusion in the table of BMP options used in Rule 40E-63.  Mandatory BMP implementation for the EAA was set for January 1995.

For more information contact: Samira Daroub or Timothy Lang