Variable Rate Application of Fertilizer in Citrus

Abstract

Spatially variable application of fertilizer to citrus fi elds is dependent upon accuracy of the input variables. The accuracy in determining a variable rate application map and the application accuracy are important. An accuracy model is described using a 3.6-ha Florida citrus block. The effects of boundary determination, interpolation method, and global positioning system (GPS) location errors were studied for determining a variable rate nitrogen application map based upon citrus yield maps. Accuracy models can be developed considering interaction among GPS horizontal accuracy, differential GPS (DGPS) sampling frequencies, and machine delay times of a hypothetical variable rate applicator for nitrogen (N) fertilizer application based on an application map. Parameters studied included fi ve GPS horizontal accuracy levels, two levels of DGPS horizontal accuracy, two DGPS sampling frequencies, and two machine delay times. Two integrated models were developed which documented the effects of the parameters. Machine delay time was the most important factor, and GPS horizontal accuracy was the second most important.