Nitrogen fertilization of bean at sowing and as topdressing under no-tillage and conventional tillage

With the aim of evaluating the responses of bean to nitrogen fertilization rates at sowing and topdressing in the field, two experiments were carried out (no-tillage and conventional tillage), in the rainy season 2004/2005. The experimental design was in randomized blocks with three replicates in a 4x4 factorial structure encompassing four N rates at sowing (0, 40, 80, and 120 kg. ha(-1)) and four topdressing N rates (0, 40, 80, and 120 kg. ha(-1)) at 20 DAE. Each plot was composed of four 5-m-long rows, 0.5 m apart from each other and a 16 seed. m-1 density was used. Initial and final stand and grain yield were assessed. In both crop management systems, the increasing nitrogen fertilization rate at sowing reduced the plant stand. In general, in no-tillage the response to N application at sowing was squared and the rate corresponding to maximum yield varied depending on the topdressing rates. In conventional tillage this response decreased linearly, as a function of the higher effect of N at sowing on final stand. The response to N topdressing application was squared in both crop management systems and higher responses to grain yield were observed with 40 kg.ha(-1) N rate at sowing.