Using Hand Held Optical Sensors to Enhance Grain Yield and NUE in Winter Wheat.

Nitrogen (N) in Kansas soils can vary dramatically over the course of a year, and from year to year. Due to the continuing drought in the Great Plains, a number of acres of winter wheat were following failed summer crops of corn or grain sorghum. Hand held optical sensors have the potential to assess the N status of winter wheat in these cropping systems and optimize N recommendations.  The objective of this study was to evaluate the effectiveness of 1^st and 2^nd generation KSU optical sensor-based N recommendation algorithms against the KSU soil test based N recommendation system.  Eight field trials across Kansas were conducted during the 2014-2015 crop year in cooperation with County Ag Agents and farmers.  Treatments consisted of an N response curve, 1^st and 2^nd generation KSU N recommendation algorithms, and KSU soil test based N recommendations applied in the spring using applied N rates ranging from 0 to 140 kg ha^-1.  The 1^st generation KSU N recommendation algorithms utilized an N reference strip to determine N sufficiency, while 2^nd generation KSU algorithms base N recommendations on potential physiological response of the crop and do not require a N reference.  Results indicate the KSU soil test and 2^nd generation optical sensor-based N recommendation algorithm were effective at determining the appropriate N recommendation across locations. Using the soil test N recommendation, growers saved approximately $39 per hectare in N cost while using the crop sensors on whole field or management zone level would save an additional 6.35 kg of N over soil testing, and saving approximately $57 in N costs per hectare.  Enhancing nitrogen use efficiency through the adoption of soil testing and/or the use of the active crop sensors is possible, and in most cases highly economical.