Variable Rate Applications of Granular Fertilizer for Citrus Test Plots

A key component in precision agriculture is exact delivery of liquid and solid materials to site-specific locations.Addressing this concern, Florida growers are in the initial phase of implementing best management practices for variouscitrus growing areas. A 16.2-ha (40-acre) field trial was initiated with a grower in the Ridge growing section of the state. Aspart of that project, prescription maps were developed for multiple dry fertilizer applications throughout the season. Agranular fertilizer unit with hydraulically powered dual split-chain outputs controlled from a MidTech Legacy 6000 controllerwas utilized. Data were collected on target and as-applied rates compensating for missing trees and resets. Additional massbalance data were obtained by weighing each load before and after spreader application. Application rates for each of43 blocks (42 test, 1 conventional) were compared for eight tests conducted during the 2002-2003 and 2003-2004 fruitseasons. Prescription and as-applied rates exhibited a high correlation (r2 = 0.98) and linear relationship (slope = 0.98).Grand totals from vehicular weighing and controller discharge estimation produced an average absolute error of 7.7%.