Simulation of Fixed and Variablerate Application of Granular Materials

Research has shown that application errors exist with variablerate technology (VRT) systems. Consequently,using prescription maps for economic and agronomic analyses can generate misleading results. The intent of this article wasto develop and validate a spatial data model for generating asapplied maps to support the advancement of precisionagriculture practices. Previous research modified ASAE Standard S341.2 to include a 2D matrix of collection pans to assessfixedrate and variablerate (VR) deposition of granular fertilizers and agricultural lime from a spinner disc spreader. Theasapplied spatial data model uses GIS functionality to generate asapplied surfaces by merging distribution patternsand a spatial field application file (FAF) into an asapplied surface representing the actual distribution of granularfertilizer or agricultural lime across a field. To validate the asapplied spatial data model, field studies were conductedby randomly placing collection pans across two fields. Murate of potash was then applied using a VR spinner spreader. Theasapplied spatial data model was used to predict the amount of material each pan should have received. Comparisonswere made between the actual and predicted application rates for two fields, with R2 values of 0.45 (field A) and 0.58 (fieldB) computed. However, R2 values of 0.16 (field A) and 0.21 (field B) were observed when comparing the actual applicationrates and prescription maps. These low R2 values indicated poor application by the spinner spreader but demonstrated thatthe asapplied model did a better job of representing the distribution of murate of potash when contrasted with theprescription maps. Asapplied surfaces provide a means for evaluating fixedrate and VR application of granular productswhile enhancing researchers ability to compare VR management approaches.