AGRONOMIC EFFICIENCY OF NITROGEN FERTILIZ ERS FOR WHEAT

Urea is the most used nitrogen (N) fertilizer in Brazil. PETROFERTIL C ompany aggregated to urea and to other N fertilizers, gypsum, ammonium sulphate, and Patos rock phosphate. In order to test these fertilizer s, three experiments were carried out with wheat, using microplots (19 84) and conventionally sized field plots (1987 and 1988). The soil was a Dark-Red Latosol (Hapolhumox), presenting 4.5% (microplots) and 2.8 % (conventional plots) of organic matter. Based on N absorption by whe at in the microplots, the following fertilizers presented values equal or above 100% agronomic efficiency (AE), using ammonium nitrate as re ference source: nitrosulfocalcium gypsum DH (113%), nitrocalcium (109% ), urea covered with gypsum (106%), urea nitrate compacted with Patos rock phosphate (105%), nitro magsulfocalcium gypsum HH (105%), and ure a compacted with ammonium sulphate (100%). Seven sources were selected from this experiment and used in the next two trials, carried out und er conventional plots. In 1987 there were no significant differences i n yield and only small differences in AE among N sources were observed . In 1988 significant grain yield diferences were obtained among N fer tilizers, being urea statistically equivalent to the following product s: urea nitrate compacted with Patos rock phosphate, urea covered with gypsum, urea covered with ammonium sulphate, and nitrocalcium. The AE of urea in this trial was 126%. It was concluded that the aggregation of various compounds to urea did not increase steadily its AE for whe at.