Evaluation of sensor-based field-scale spatial application of granular N to maize

Improved genetics and better management have increased maize productivity, but often at the expense of excess water and N fertilizer. Environmental concerns have prompted the development of precision technologies and associated management strategies intended to increase crop N use efficiency. This study evaluated the effectiveness of variable-rate application (VRA) of granular N fertilizer to maize when N requirement was computed using the Holland-Schepers algorithm in field experiments conducted in central Greece from 2015 to 2017. In plot-scale trials, the algorithm applied 34-51% less in-season N, or 13-31% less total N, without any yield losses when compared to the conventional practice. An Economic Optimum N Rate was applied under field-scale conditions when the algorithm computed N rates on-the-go to guide a variable-rate spreader for spatially adjusted N rates with 1-m on-the-row precision. The VRA system delivered on average 34% less in-season N, or 24% less total N, than the farmer rate. As a result of reduced N inputs, VRA improved the agronomic N-use efficiency by 21 to 30%, decreased soil nitrate levels by 22 to 70% and increased returns over N cost by euro33 to euro92/ha in all trials compared to the conventional practice. These economic estimates do not include the VRA technology costs, and they also do not consider the environmental benefits arising from improving water and soil quality.