STARTER NITROGEN FERTILIZATION IN DIFFERENT SOYBEAN CULTIVARS

Although several studies have already been carried out on biological nitrogen fixation, there are still recurrent questions, especially among soybean farmers, about the need for nitrogen at sowing, in early soybean cultivars, in crops with high yield. Thus, the objective of this work was to evaluate the effect of nitrogen fertilization on different soybean cultivars, with different cycles. The experiment was carried out at Fazenda Recanto, in the municipality of Carmo do Rio Claro, MG, in two harvests (2016/2017 and 2017/2018). It was carried out in a randomized block design, in a split-plot scheme, with four replications. The plots were composed in the 2016/17 harvest by three soybean cultivars (M6410 IPRO, NS7300 IPRO and TEC7849 IPRO), and in the 2017/18 harvest by four cultivars (M5917IPRO, M6410IPRO, AS3680IPRO, NS7670RR), while the subplots consisted of four doses of nitrogen at sowing (0, 10, 20, 40 kg ha-1). Grain yield, number of nodules per plant, mass of dry nodules per plant, number of grains and pods per plant, plant height and insertion of the first legume were evaluated. Experimental data were subjected to analysis of variance, and means were compared using the Scott-Knott test at 5% probability. The doses of nitrogen at sowing did not influence yield and agronomic characters of cultivars evaluated in the 2016/17 and 2017/18 crops. Increasing doses of nitrogen inhibited soybean nodulation.Although several studies have demonstrated that biological nitrogen fixation can provide the nitrogen required by soybean, doubts regarding the need for nutrient application at sowing, specifically "starter N," in early soybean cultivars persist, particularly in high-yielding crop fields. Thus, this study aimed to evaluate the effect of starter nitrogen fertilization on soybean cultivars with different maturity cycles. The experiment was conducted at Fazenda Recanto, in Carmo do Rio Claro, Minas Gerais state, during two crop seasons (2016/2017 and 2017/2018), using a randomized complete block design with split-plot arrangement and four replications. In the 2016/17 cropping season, the plots were comprised of three soybean cultivars (M6410 IPRO, NS7300 IPRO, and TEC7849 IPRO). In the 2017/18 cropping season, the plots consisted of four cultivars (M5917 IPRO, M6410 IPRO, AS3680 IPRO, and NS7670 RR). The subplots were assigned four nitrogen doses at sowing (0, 10, 20, 40 kg ha-1). Grain yield, number of nodules per plant, mass of dry nodules per plant, number of grains and pods per plant, plant height and insertion of the first legume were evaluated. Experimental data were subjected to analysis of variance, and means were compared using the Scott-Knott test at 5% probability. The nitrogen rates at sowing did not influence soybean yields and agronomic characters of cultivars evaluated in the cropping 2016/17 and 2017/18. Increasing doses of nitrogen inhibited soybean nodulation