Irrigation increases the probability to obtain high crop grain yield, but demands a technical and economical reasonable use of agricultural inputs, especially nitrogen fertilizers. The objective was to determine the more adequate rates of nitrogen and potassium for corn (Zea mays L.) grain yield and the better economical return of the fertilization in corn under sprinkle irrigation. The experiment was carried out in the years 2002/03 and 2003/04 in Cruz Alta-RS, Brazil, in a crop farm using central pivot irrigation system. The soil used was an Oxisol (Hapludox). The corn effective population totalized 78.000 and 71.000 plants ha-1 for the years 2002/03 and 2003/04, respectively, using the hybrid Pioneer 30F44. The treatments were composed by 0, 80, 120, 160, 200 and 240kg ha-1 of N (urea) combined with 0, 40, 80 and 120kg ha-1 of K2O (potassium chloride). The experiment was set in a randomized block design with four replicates. The maximum corn grain yield under sprinkle irrigation was obtained with N rates between 283 and 289kg ha-1, but the maximum economic efficiency was between 156 and 158kg of N ha-1, without any increment in grain yield with potassium application. These results show that, in many situations, farmers are using rates of nitrogen and potassium fertilizers over than necessary.
nitrogen rates; potassium rates; maximum technical efficiency; maximum economic efficiency; corn fertilization; irrigation
