Precision nitrogen fertilizer management of maize and cotton using crop sensors

摘要

Nitrogen fertilizer greatly increases crop yields but requires large amounts of energy to produce and has undesirable off-site effects when it escapes from agricultural systems. Precisely matching N fertilizer rates to crop needs maximizes benefits while reducing negative impacts. Soil N supply to crops is spatially variable, so spatial diagnosis is needed to apply optimal N rates. Crop reflectance sensors provide an accurate and spatially-intensive method for diagnosing and applying the correct N rate. We have developed calibrations relating optimal N rate to reflectance ratios for maize and cotton. These calibrations require that sensor reflectance measurements be expressed as a ratio with measurements from high-N areas that are matched in growthstage, genetics, and environment. We have used these calibrations in demonstrating sensor-guided N applications to maize and cotton producers. Side-by-side replicated comparisons of sensor-based variable-rate N and producer-chosen N rates for 53 maize fields resulted in N savings of 16 kg N/ha and a yield increase of 110 kg grain/ha. Results from our first four demonstrations in cotton fields should be available by the time of the congress. Drift of sensors during the course of a day has been an unexpected obstacle and requires frequent re-measurement of the high-N reference area.