Editor's note: A special thanks to Dr. Monica Ozores-Hampton at the Southwest Florida Research and Education Center for coordinating The Immokalee Report, of which the article below is part.

The emphasis of the soil and water science research and Extension program in South Florida is the evaluation of best management practices (BMPs) with emphasis on crop nutrient and water use.

BMPs have water quality protection as a goal, but it must be balanced with maintaining the grower’s ability to produce acceptable economic crops.

As we all know, the sandy soils of South Florida have poor water and nutrient retention. Therefore, adequate irrigation and nutrients are required for optimal crop production.

Research and Extension demonstration projects conducted in southwest Florida center around use of nitrogen and phosphorus by the crop plants, movement of these vital nutrients within the soil at a field scale and their impact on water quality.

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 BMPs to correspond with crop nutrient demand are among the BMPs being evaluated. Recently, citrus greening has increased the emphasis tree nutrition with evaluation of new production systems and use of foliar sprays to reduce disease symptoms.

Controlled-release fertilizers have been used on young citrus trees for a number of years. These fertilizers have been shown to improved tree growth with reduced application costs and leaching.

Recent demonstrations have shown that sugarcane yields can be maintained with one-third less nitrogen and have resulted in increased use of these fertilizers. Similar work is being conducted on vegetable crops, with more controlled-release being used on those crops as well.

 Higher pH may affect phosphorus availability

A statewide trend is the increase in soil pH with long-term agricultural production. A demonstration project in South Florida on soils with pH of more than 6.5 and high calcium content has shown the importance of maintaining soil pH in an appropriate range of about 5.5 to 6.5.

Phosphorus becomes less available at high pH, so growers in some areas find it necessary to add phosphorus to their fertilizers even if the soil test indicates a high amount of phosphorus in the soil.

Revised soil test recommendations are being developed for these soils and will help growers to apply the proper amount of phosphorus without increased impact on surface water quality.

Advanced production systems for citrus

Field work on citrus to establish new advanced production systems with higher tree densities and improved nutrient management is being conducted in South Florida.

The open hydroponic system uses fertigation intensively and has been shown to improve early growth and production of citrus. This has become more important because citrus greening has reduced production in some groves and increased production costs in nearly all groves.

The increased growth and productivity of young trees will increase the grower’s profits. Greening is known to reduce the leaf content of several key nutrients. Greening symptoms can be reduced and tree growth improved with foliar sprays of these nutrients.

Research work in South Florida is being conducted to determine the amounts and proper timing of these nutrient applications.

Kelly T. Morgan is an assistant professor and soil scientist at the Southwest Florida Research and Education Center. He can be reached at conserv@ufl.edu.