Yield and Agronomic Efficiency of Maize under Conventional and Enhanced-efficiency Nitrogen Sources

Several factors interfere with the agronomic efficiency of nitrogen fertilizers, which may be related to the soil, crop, management and source used. The aim was to evaluate and compare the efficiency of nitrogen sources and rates in top-dressing on maize agronomic traits in two seasons. The experiment was conducted in southeastern Brazil in a randomized block design, with four replicates. Treatments were distributed in a 3 x 3 + 1 factorial scheme, using three sources of N (conventional urea, ammonium nitrate and compacted urea with additives and polymers) and four N rates (0, 70, 140 and 210 kg ha- 1), applied in top-dressing 18 days after maize emergence in both seasons (phenological stage V4). Compared to conventional urea, compacted urea promoted maize yields up to 30% and 19% higher in the first and second seasons, respectively. Based on regression analysis, maximum grain yields of 12,297, 12,089 and 9,485 kg ha- 1 were obtained in the first season when compacted urea, ammonium nitrate and conventional urea were used at rates of 162, 168 and 195 kg ha- 1 of N, respectively. Compacted urea reduces nitrogen requirements by up to 17% compared to conventional urea for maximum maize yield. There was greater agronomic efficiency for compacted urea and ammonium nitrate. The highest agronomic efficiencies occurred at the rate of 70 kg ha- 1, regardless of the N source and the seasons. These results demonstrate the benefits of compacted urea with additives and polymers in increasing maize yield, in addition to allowing N rate reduction for maximum yield.