Red Edge as a New Index for Determining Optimum Mid-Season N Rate Fertilization in Winter Wheat.

Efficient use of nitrogen (N) is crucial in crop production due to the continuous increase in fertilizer costs and rising environmental concerns. To increase N use efficiency (NUE), Oklahoma State University (OSU) has developed an N algorithm for determining optimum N rates for mid-season fertilizer application in winter wheat. Optically generated normalized difference vegetation index (NDVI) sensor readings (780 nm-670nm)/(780nm+670nm) are  most widely used for evaluation of plant N status and is a key input for the OSU algorithm. However, it has been reported that under certain conditions NDVI has low sensitivity.  To overcome this limitation, other researchers have proposed the use of red-edge (700nm -740nm) that has been tested as new index for assessing N response. The objective of this study was to determine whether the red-edge index has the potential to be a better detector of N stress, and  that would ultimately provide more accurate fertilizer N recommendations for winter wheat compared to NDVI.