Nitrogen fertilization in soybean under low latitude and low natural soil fertility

In soybean, some studies have shown yield increase when nitrogen is provided through symbiotic fixation along with nitrogen fertilization. Thus, this study aimed to evaluate the effect of nitrogen fertilization on soybean cultivated at a low natural fertility area. Two experiments (field and pot) were conducted. A randomized block design was adopted, with 24 treatments and 3 replications. The treatments were arranged in a 2x12 factorial scheme, represented by two cultivars (TMG 1288RRTM and CD 251RRTM) and 12 combinations of nitrogen supply (CNS). The CNS used were: without inoculant and nitrogen; only inoculant; 20; 40 and 60 kg ha-1 of N + inoculant; 50; 100; 150; 200; 250; 300 and 350 kg ha-1 of N. The doses of N were divided into three applications: 20% applied at planting, 40% at early flowering and 40% at grain-filling. The nitrogen fertilization associated with seed inoculation did not result in significant gains for crop yield. The mineral nitrogen supply affected negatively the number and mass of nodules, and positively the root mass.