Nitrogen and Cropping Systems on Soybean Establishment.

Soybean plant establishment relies on several factors and may influence the final yield. One of them that should be managed by farmers in tropical regions, such as Brazil, is the preceding crop, which can provide different mulch and affect soil structure. The aim of this research was to evaluate previous cropping systems associated with nitrogen (N) fertilization on soybean stand (plants ha^-1) in the 2014/2015 season. The systems were composed of crops grown during fall/winter, harvested and chemically managed before sowing soybean in the spring. These crops were: maize (Zea mays); maize intercropped with Urochloa ruziziensis; maize intercropped with Urochloa brizantha; Urochloa ruziziensis; Urochloa brizantha; millet (Pennisetum glaucum); and the association of radish (Raphanus sativus L.) and black oat (Avena strigosa). Ammonium nitrate was applied on these fall/winter crops providing 0 and 100 kg ha^-1 of N. The experimental design was 7x2 split-plot in randomized blocks with four replications. The plots were carried out under field conditions in a distroferric Red Nitisol of Itambe, Parana, Brazil. At the time of soybean harvest, plant population were assessed. It was influenced only by the cropping systems (P<0.01). The plots with U. brizantha and P. glaucum provided the higher values, 210.077 and 200.354 plants ha^-1, respectively. These better treatments differed and exceeded significantly from maize and maize with U. brizantha (175.006 and 165.631 plants ha^-1). These results may be related to a 20-day drought after the soybean was sown, consequently the plots which had higher organic material input, and better soil surface cover may have retained moisture from the previous rainfall, bringing benefits for soybean establishment.