بهینه سازی مصرف کود در گندم با استفاده از شاخص تغذیه نیتروژن

To determine nitrogen nutrition index for wheat cultivars a field experiment was conducted with factorial arrangement based on complete randomized block design with 3 replications. Experimental factors included 3 wheat cultivars (Chamran, Gaskogen and Sionez) and 4 nitrogen application rates (0, 55, 110 and 170 kg N ha-1). Shoot dry matter and nitrogen concentration was measured in 5 sampling during vegetative growth period. Using these data critical N concentrations and critical N dilution curve calculated and compared with the reference dilution curve for wheat crop. Critical concentration were slightly underestimated by the curve obtained in this study however, estimated coefficients of the dilution curve were closed to those of reference curve. Overall, nitrogen deficiency, sufficiency and excess in shoot dry matter were properly described by the estimated critical dilution and critical uptake curves. All wheat cultivars were nitrogen limited in control and 55 kg N ha-1 however, in 170 kg N ha-1 shoot nitrogen content was more than amount required for optimal growth and in 110 kg N ha-1 nitrogen uptake was closed to critical values. Nitrogen nutrition index (NNI) was calculated as the ratio between measured shoot N (%) and the critical N concentration. In control and 55 kg N ha-1 NNI was lower than 1 during the whole vegetative growth period. However, in 110 kg N ha-1 NNI was almost 1 and in 170 kg N ha-1 varied between 1-1.3. A significant relation was obtained between NNI at flowering and relative yield of wheat cultivars and grain yield of 3 cultivars reached to its maximum at NNI=0.9-1. Grain protein was also linearly correlated with NII at flowering. Based on the results nitrogen nutrition index calculated from critical dilution curve could be used for precise estimation of crop growth rate, dry matter accumulation, grain yield and grain protein and to optimize N fertilizer required for any predefined yield level.