Late supplemental nitrogen fertilization on soybean cropped in Cerrado Oxisols

The objective of this work was to evaluate the effects of nitrogen fertilization at the pre-flowering (R1) and seed filling (R5) stages, on the nodulation and yield of soybean grown in Cerrado Oxisols. The study was performed for seven years in a clayey Typic Haplustox, and for four years in a clayey Rhodic Haplustox, both with established populations of Bradyrhizobium. Fifteen experiments were carried out under conventional and no tillage management systems and the treatments were: standard inoculation (SI) with B. japonicum; SI + 200 kg ha(-1) N (urea), split-applied 50% at sowing and 50% at the R1 stage; SI + 50 kg ha(-1) N (ammonium nitrate) in R1; SI + 50 kg ha(-1) N (ammonium sulfate) in R1; SI + 50 kg ha(-1) N (ammonium nitrate) in R5; and SI + 50 kg ha(-1) N (ammonium sulfate) in R5. The application of 200 kg ha(-1) N harmed nodulation. In only two experiments, the yield responses to late season N applications were significant, with no net economical benefits or the producer. Late nitrogen fertilization on inoculated soybean, grown under Brazilian Cerrados Oxisols, has no economical advantages in any of the management systems evaluated, regardless of the N source applied.