Precrops and N-fertilizer impacts on soybean performance in tropical regions of Brazil

Precrops have different growth patterns, nitrogen (N) requirements, and production of residues varying in amounts and quality that may affect the N-clycling and the soybean (Glycine max L. Merrill) cropped in succession. This study aimed to evaluate the effect of precrops and N fertilization on soybean performance. An experiment was conducted in Londrina, Paraná State, Brazil, with six precrops treatments: fallow, ruzigrass (Urochloa ruziziensis), showy rattlebox (Crotalaria spectabilis), corn (Zea mays) without or with 80 kg ha−1 of N at topdressing as urea, and wheat (Triticum aestivum). Subplots consisted of two levels of N fertilization at soybean sowing: 0 and 30 kg ha−1 of N as ammonium nitrate at sowing. Urochloa ruziziensis as precrops increased the soybean yield (5,171 kg ha-1) when compared with corn (4,346 kg ha-1) and fallow (4,467 kg ha-1). In 2016/17, N fertilization of soybean with 30 kg ha−1 of N at sowing, although increasing the initial plant growth (745 kg ha-1 with vs. 662 kg ha-1 without), impairs nodulation (100 mg pl-1 with vs. 130 g pl-1 without) and does not increase grain yield. Oil and protein concentrations in soybean grains are not influenced by precrops and N fertilization at sowing. We found that the use Urochloa ruziziensis as cover crop in soybean precrops is a good recommendation option in tropical regions of Brazil, because increasing the yield of soybean grown in succession. N fertilization at in soybean sowing it should not be recommended even in the presence of a large amount of straw.