Spatial Variability of Soil Chemical and Biological Properties in Florida Citrus Production

Soil and yield variability is a common problem in Florida citrus production; however, only limited progress has been made in charactering and identifying major yield-limiting properties. This study characterized the variability in soil chemical and biological properties. To achieve this, a citrus grove was divided into five productivity zones based on tree canopy volume (0-1.84, 1.84-3.67, 3.67-5.51, 5.51-7.34, and 7.34-9.18 m(3) m(-1) row for very poor, poor, medium, good, and very good, respectively) using geographic information system soft ware. Six random soil samples were collected from each productivity zone at four depths (0-15, 15-30, 30-45, and 45-60 cm) to analyze various soil properties. Soil organic matter, Mehlich I extractable P, K, Ca, and Mg, and oxalate-extractable Fe and Al varied greatly along the productivity gradient, and their differences among zones were most prominent in the lower soil depths. These soil properties had a common pattern of spatial distribution (range 150-200 m) that matched the variation in fruit yield. The results of discriminant function and partial least squares regression analyses revealed that the productivity within the grove differed in the 0- to 60-cm soil depth, signifying that greater root zone depths could better explain the differential productivity of citrus groves than the 0- to 15-cm layer, which is the depth used presently for fertilizer recommendations. Collectively, our results suggest that soil sampling depths for citrus should be 0 to 60 cm and sampling should be done based on the variogram range of easily measured soil properties.