Calibrating in-Field Diagnostic Tools for Improved Nitrogen Management in Spring Wheat.

The objectives of this research were to determine whether adding nitrogen (N) fertilizer at a given point in the season is likely to increase wheat yields and/or protein content, and to develop tools and metrics that indicate how much fertilizer to apply to meet yield and protein goals. In order to accomplish these objectives, wheat was grown in several California locations with variations in the rate and timing of N fertilizer application. Treatments included N rates ranging from 0 to 336 kg/ha N and applications occurring pre-plant, at tillering, boot and flowering, and in various combinations of these timings. To assess the status of the wheat crop in real-time, sensors and tools designed for in-field use that give immediate feedback as to the N status and overall health of the crop were also calibrated. The hypothesis was that split fertilizer applications would improve the nitrogen use efficiency (NUE) of the crop and that in-field tools would give the grower an opportunity to better adapt their fertility plan to in-season conditions. We found that: 1) split applications significantly improved yield, protein and NUE outcomes (p<0.01), particularly at moderate to low rates of N fertilization; 2) the use of in-field sensors provided actionable, real-time information as to the protein and protein-yield outcomes; and 3) combining information from more than one sensor resulted in additive information that improved the in-season ability to predict outcomes. This information could lead to more precise and efficient N management, resulting in a more productive and profitable wheat crop in the state of California.