| Soil variability is a common problem in Florida citrus production. However, only limited progress has been made in characterizing and managing soil variability to identify and rectify the limitations, to maximize profit, or reduce environmental impacts.;Therefore, this study was designed to characterize wide-ranging aspects of variability in these sandy soils and to develop methods to ameliorate critical limiting factors affecting Florida citrus production. To achieve this, a citrus grove was divided into five productivity zones based on tree canopy volume using geographic information system software. These five zones were termed "very poor," "poor," "medium," "good," and "very good" productivity zones. To characterize horizontal and vertical soil variability of chemical, physical, mineralogical and biological properties, six random soil samples were collected from each productivity zone at depth increments of 0--15, 15--30, 30--45 and 45--60 cm. Soil organic matter, nutrient concentrations, soil color, sand content and water retention parameters varied greatly along the productivity zone and the soil depth. Soil organic matter, sand grain coatings, soil color and soil permanent wilting point contributed significantly to the predictive models developed using partial least squares (PLS) regression. These models explained 54 to 71% variance for canopy volume, which increased with the increased root zone depth. For amelioration, two greenhouse experiments with sorghum and radish as bioassay crops were used to study productivity zone, water content, soil amendment, and rate of amendment. The results revealed that application of cheap byproducts like phosphatic clay or iron water treatment residuals at 5 % rates can increase water retention and productivity in the poor areas. These amendments can be cost effective when applied at planting to each tree, and can increase profit in few years when applied to low-yielding areas. In addition, applying frequent small irrigations can enhance water availability in the excessively drained sandy soils of the weakest production zones.;The results of this study will assist in planning soil sampling, characterizing soil variability, making land use decisions, and ameliorating unproductive areas of both new fields and established citrus groves. Careful management of soil variability can improve crop production, increase revenue, and reduce potential environmental contamination. |
