Improving nitrogen efficiency of maize (corn) using crop sensors

Peter Scharf 1

1 University of Missouri, 108 Waters Hall, Columbia, MO, 65211, U.S.A.,,,


Nitrogen fertilizer has a tremendous impact on crop growth and is essential for feeding the 7.4 billion people on Earth.  It is also the most energy-intensive input to crop agriculture, has a proclivity to escape from ag systems, and has negative off-site impacts when it escapes.  For all of these reasons, efficient use of N fertilizer is essential.  Crop sensors are a promising approach to optimize N fertilizer application rate and timing.  Three separate experiments with maize (corn) helped to define the N efficiency gains to this approach.  One experiment group involved 55 field-scale experiments in which the farmer’s N rate was compared to variable-rate N based on crop sensors.  System efficiency (N removed in grain/[N applied as fertilizer + manure]) was 0.68 with the farmer’s chosen rate, and increased to 0.78 with sensor-chosen N rates.  A second experiment was initiated in 2007 to compare N fertilizer rate and timing decision systems.  For 2007-2014, the most profitable pre-plant N rate (200 kg N ha-1) gave system N efficiency of 0.43, while sensor-based N rate gave system N efficiency of 0.74. The third experiment was initiated in 2012 and compared a pre-plant N rate of 155 kg N ha-1 with sensor-based variable-rate N.  System efficiency for pre-plant N was 0.51, and for sensor-based N was 0.57.  In the latter two experiments, pre-plant N treatments had low efficiency in years with high spring rainfall.  Timing of N probably improved N efficiency more than improved N rate.