Nitrogen fertilization, inoculation and soil liming dates for soybean cultivated in cerrado soil

Abstract

A field experiment was carried out with soybean (Glycine max (L.) Merrill) to gain information about the necessity of the application of starter N fertilizer under conditions of low available soil nitrogen. Available N was modified by incorporating 26 t/ha of plant litter and by the application of lime at two dates (80 and 30 days before planting) in virgin Red-Yellow Latosol. Nitrogen uptake in uninoculated soybeans was reduced in the late liming treatment. Inoculated soybeans however, showed no response to date of liming or to rates of N starter fertilizer (0, 10, 20 and 30 kg/ha, applied at 4 days) showing that even when available soil nitrogen is low, starter nitrogen is not necessary. The nodules appeared on the 5^th day and an evaluation carried out on the 12^th day showed that the plants already had a reasonable high level of N₂ fixation in all treatments. Periodical evaluation showed that the nitrogenase activity reached its maximum immediately after flowering, decreasing sharply after the end of pod-filling.