Kirandeep Mann, Univ of Florida, 700 Experiment Station Rd, Lake Alfred, FL 33850, Arnold Schumann, Univ of Florida-CREC, 700 Experiment Station Rd, Lake Alfred, FL 33850, Thomas Obreza, Univ. of Florida, PO Box 110290, PO Box 110290, Gainesville, FL 36211-0290, United States of America, and Wonsuk D. Lee, UNIVERSITY OF FLORIDA, Frazier Rogers Hall, Room 227, GAINESVILLE, FL 32611.
Spatial yield reduction and soil heterogeneity were studied in a Florida citrus grove (10 ha) located near Wauchula in Hardee County, Florida to identify soil properties responsible for differentiating soil productivity. Tree canopy volumes were measured and mapped in the grove using an ultrasonic array and DGPS receiver in order to quantify productivity. The grove was classified into five groups of management zones as representative of very good, good, medium, poor and very poor growth areas. Soil samples were collected at 30 representative locations at 4 profile depths (0-15, 15-30, 30-45, 45-60 cm) and analyzed for their pH, organic matter (OM), Mehlich I- extractable nutrients and cation exchange capacity (CEC). Fruit yield was mapped from harvester trucks equipped with DGPS receivers and data loggers, and the normalized difference vegetation index (NDVI) was calculated from color-infrared aerial photographs of the grove. The soil properties averaged over the productivity category showed a continuous decrease with the depth. The regression analysis showed that 77 % of spatial variation in canopy was explained by average soil profile properties including OM, CEC, pH, P, K, Ca, Mg, Fe and Mn. Out of this 55 % variation was explained by only OM and CEC. The effect of these soil properties on canopy volume increased up to a depth of 30-45 cm. The poor areas of the grove were found to be located on the St. Lucie fine sand. The OM, CEC, P, K and Ca showed a very good correlation with the canopy volume showing the lower values in the center of the grove from North to South and high values in eastern and western parts. The results indicated the need for site-specific management for the poor areas of the grove on the basis of easily measured soil properties like organic matter.
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