Potential for Fine-Tuning Rates of Nitrogen Using in-Crop Applications of Nitrogen Based on Greenseekertm Readings in Spring Cereals on the Canadian Prairies.

Nitrogen is the most limiting nutrient to crop production on the Canadian Prairies. Of the four factors encompassing nitrogen management, form, timing, placement and rate, deciding on a rate of nitrogen is the most challenging because of the spatial and temporal variability of crop nitrogen requirements and the soils capacity to supply N. Studies were established to develop appropriate algorithms for the GreenSeeker^tm optical sensor in spring cereals and to then test the algorithms in separate but adjacent areas. Yield potentials were generated using different rates of nitrogen and sensor values were related to final grain yield using an exponential function, y=a*exp b*x where y=grain yield and x=(sensor readings-NDVI divided by growing degree days from planting to sensing using a base temperature of 0^oC). The crops of interest were spring wheat, durum, oat and barley. The algorithms for each crop were then evaluated for their ability to manage nitrogen relative to uniform rates of nitrogen applied at time of planting in the soil. The risks of in-crop applications of nitrogen were also determined as part of the test treatments. The study supports the merits of in-crop N applications for all crops measured. Post-emergent N applications, when combined with optical sensors, offers the possibility of refining N rates to match the crop with soil and crop conditions and to also take into consideration spatial variability in soil nitrogen.