Estimation of Optimum Nitrogen Fertilizer Rates in Winter Wheat in Humid Mediterranean Conditions, I: Selection of Yield and Protein Response Models

Nitrogen (N) fertilization management directly affects yield and grain protein content of soft red winter wheat, so there is a need to estimate the optimum N fertilizer dose needed to obtain the greatest yield and the desired protein content under a humid Mediterranean climate. The objective of this work was to select the best response models of wheat yield and protein content to applied N fertilizer. To fulfil this objective, 13 experiments were conducted in the years 2001, 2002, 2003, and 2004 in northern Spain where 0, 100, 140, 180, and 220 kg N ha–1 were applied. The quadratic plateau model best described yield response to N fertilizer, with 182 kg N ha–1 producing the maximum yield. The quadratic model was chosen for modeling protein response to N fertilization, and 176 kg N ha–1 was the rate required for achieving protein contents greater than 125 g kg–1.