Evaluation Of Sensor Based Technology For Improved Nitrogen Recommendation For Winter and Spring Wheat In Montana.

Nitrogen (N) is the most limiting nutrient source for winter and spring wheat. Nitrogen is a key nutrient important for wheat growth and development, grain yield and grain quality, including protein content. Precision agriculture tools such as sensor based technologies allow us to optimize the yield with precise application of nutrients. Remote sensing is a precision agriculture technique that quantitatively measures vegetation indices such as the Normalized Difference Vegetation Index (NDVI). The feasibility of various sensor-based systems must be evaluated before a recommendation can be made as to what system is more efficient and appropriate for Montana conditions. The major objectives of this study are: I) to evaluate two sensors – GreenSeeker (GS), and Pocket Sensor (PS) – for measuring spring wheat and winter wheat canopy reflectance and II) to correlate grain yield at different soil N levels using the GS and PS. Winter wheat and spring wheat field experiments were established at Western Triangle Agriculture Research Center (WTARC), Conrad, MT, in 2012. At seeding, N rates of 0, 20, 40, 60, 80, and 220 lb N ac^-1 and 0, 40, 80, 120, 160 and 200 lb N ac^-1 were applied to spring and winter wheat respectively, as side banded urea (46-0-0) to simulate a range of N levels. The NDVI readings from each treatment were collected at Feekes 5 growth stage utilizing the GS and PS. For both spring and winter wheat, the NDVI measurements obtained with the GS and PS were highly correlated (R² = 0.7). The NDVI measurements were found to be highly influenced by the N application rate (R² ranged from 0.4 to 0.95). Depending on the N rate, between 30 and 99 % of variation in wheat grain yield was explained by the variation in the NDVI. About 67% and 80 % yield was mainly influenced by the rate of N fertilizer of spring and winter wheat, respectively. The yield response to N diminished at 80 and 120 lb N ac^-1 for spring and winter wheat, respectively. Both sensors were useful in estimation of final wheat grain yield at most N levels. The GS NDVI shows better correlation with spring and winter wheat yield compared to PS NDVI at different N levels.