Production of nutrients in dual-purpose wheat pastures managed with different doses of nitrogen as topdressing - exponential model.

The aims of this study were to evaluate the yield and composition of dual-purpose wheat pasture BRS Tarumã managed with various urea nitrogen (N) doses and validate an exponential model and compare nutrient production costs. The completely randomized design had four replications per treatment (0, 150, 250, 350, and 450 kg N ha-1). For the 350 and 450 kg ha-1 treatments, the cycle was 212 d whereas that of the control was 167 d. The control accumulated 1,771 kg ha-1 dry matter. In contrast, the 450 kg ha-1 treatment accumulated 7,011 kg ha-1 DM. Topdressing nitrogen (150, 250, 350, and 450 kg ha-1) increased the traditional average daily accumulation rate by 586% relative to the control. However, the degree-days method determined a daily accumulation rate 652% higher than the control. The levels of dry matter and other nutrients in BRS Tarumã wheat pasture were influenced by the doses of nitrogen in the topdressing under the same environmental conditions (temperature and rainfall). An exponential model explained the dynamics of nutrient accumulation and was based on the thermal sum of each nitrogen dose impacting the cost per kilogram of pasture produced.