Characterization and Amelioration of Yield-Limiting Soil Variability in Florida Citrus Production.

Spatial soil variability was characterized to identify the critical limiting factors affecting Florida citrus production and to ameliorate the poor areas of the citrus groves. 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 as “very poor,” “poor,” “medium,” “good,” and “very good” productivity zones. For characterization of soil chemical, physical, mineralogical and biological properties, six locations were selected from each productivity zone to collect soil samples at four depths (0-15, 15-30, 30-45 and 45-60 cm). The relationships between citrus production and soil properties at four cumulative depths (0-15, 0-30, 0-45 and 0-60 cm) were evaluated using various statistical methods including correlation, stepwise multiple linear regression, partial least squares (PLS) regression, cluster, and discriminant function analyses. Soil organic matter, sand grain coatings, soil color and soil water content at permanent wilting point could explain the large variability in the citrus production and this contribution increased at greater depths. The predictive models developed using PLS regression analysis could explain 45 to 58 % and 54 to 71 % variance for yield and canopy volume, respectively and this variance increased with the increased depth.  For amelioration, two greenhouse experiments with sorghum and radish as bioassay crops were used to study productivity zones, 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. 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 careful management of soil variability to improve crop production, increase revenue, and reduce potential environmental contamination.