Top-Dress N Application Timing in Wheat.

This study was conducted to determine the impact of delaying top-dress application of nitrogen (N) in winter wheat after visual response has been documented. The study attempted to identify critical thresholds for days after response or response index at which maximum yield can no longer be achieved. The final objective was to document the impact of delaying nitrogen application on components and outputs of the Nitrogen Fertilization Optimization Algorithm.

A N-rich strip with N rate of 100 kg ha^-1 was established at planting as basis for visual difference comparison. The N-Rich strip N fertilizer applied was ammonium nitrate (AN). For the top-dress fertilization, AN was used as N source and was broadcasted in the experimental plots. Nitrogen was applied at the rate of 100 kg ha^-1at 0, 7, 14, 21, 28, 35, 42, 49, 56, and 70 positive growing degree days (GDD) after first visual symptom difference among the N-rich strip and the other plots. Normalized Difference Vegetation Index (NDVI) measurements was taken each 7 GDD after the first visual symptom difference among the N-rich strip and the others treatments were observed. The NDVI will be used to calculate response index (RI_NDVI). The RI_NDVI is a component of the Nitrogen Fertilization Optimization Algorithm (NFOA) which utilizes the NDVI measurements of the N-Rich Strip and farmer practice to determine top-dress N rate. At the maturity grain yield will be collected and grain quality and protein will also be analyzed. The data is under analyses and the results will follow.