Spatial Variability of Soil Physical Properties Affecting Florida Citrus Production

Abstract

Spatial variability of citrus yield is very common in Florida, but very little has been done to identify the responsible soil factors. Our objective was to characterize variations in soil physical properties in sandy soils where citrus is produced in Florida. A citrus grove was divided into five productivity zones defined as "very poor," "poor," "medium," "good," and "very good" based on tree canopy volume. Six random soil samples were collected from each zone at depths of 0 to 15, 15 to 30, 30 to 45, and 45 to 60 cm. Samples were analyzed for soil color, particle size and sand size distribution, and water retention parameters. Although the coefficients of variation (1%-60%) were large for color, texture, and water retention, the values were generally higher in areas with large trees and vice versa. The trend was opposite for soil lightness and sand content, which were lower in areas of greater growth. Most of the soil properties had a large spatial variation with semivariogram range of 100 to 250 m and varied greatly with increased productivity. Differences between the productivity zones were even more prominent at greater soil depth. Characterization and quantification of spatial soil variability in citrus groves would assist in planning future soil sampling in new fields showing soil and/or tree growth variability. The selection of soil sampling sites should be based on the sampling interval suggested by the variogram range (<75 m) and include the depth (45-60 cm) influencing productivity.