ABSTRACT One of the pillars of a no-tillage system is the addition of adequate amounts of residue to keep the soil continuously covered. Cover crops are a tool for supplying the demand for the permanence of residues on the soil surface and releasing nutrients to the soil. However, there is no index that relates these two factors and can reconcile the maximum permanence of crop residues in the soil with the maximum N supply via N mineralization of such residues. This study aimed to assess the effect of different cover crops on the decomposition rate of residues and N release, using the residual biomass quality index (RBQI) to evaluate cover crop systems. The study was conducted in a long-term experiment in a Latossolo Vermelho (Ferralsol, Oxisol) under no-tillage in the two agricultural years 2017/18 and 2018/19. The experiment was in a split-plot factorial scheme with eight winter cover crops and three N rates in randomized blocks with three replications. The cover crop systems were black oat (O), common vetch (V), forage radish (R), white lupine, rye, annual ryegrass, oat + vetch (O+V), and oat + vetch + radish (O+V+R). The N rates applied to the corn in succession were 0, 90, and 180 kg ha-1. The decomposition rate, remaining dry mass (RDM) on the soil surface, N release rate, and N accumulated release (NAR) were assessed using litterbags. Considering NAR and RDM evaluated for up to 105 days, the N release index (NRI) and remaining dry mass index (RDMI) were determined, and the residual biomass quality index (RBQI) was obtained using the product of these variables. The consortia O+V+R and O+V resulted in a decomposition rate and N release rate closer to the rates observed for oats and rye. The NAR was similar to that observed for Fabaceae species, and the RDM was similar or superior to that found for black oat. With these characteristics, the systems in the O+V+R and O+V consortia presented the highest values of RBQI, ranging from 0.61 to 0.90, indicating that RBQI is a potential indicator for choosing cover crop systems that promote greater sustainability of the no-tillage system. The use of N fertilizer in corn did not change the rates of decomposition and N release from the residues of cover crops.

ABSTRACT The objective of this work was to evaluate the management of nitrogen fertilization in grains of sorghum inoculated or not with Azospirillum brasilense in single crop or intercropped with Urochloa brizantha (cv. Paiaguás) in the off-season. The experimental design was a completely randomized block design with four replications, in a 2 x 2 x 3 factorial scheme, with sorghum in single-cropped system or intercropped with grass; sorghum seeds inoculated or not with A. brasilense; and N management (application of 100% of the dose at sowing or only in topdressing or split - 30% at sowing and 70% in topdressing) at a dose of 120 kg ha-1 N. Morphological components and sorghum grain yield and productivity of dry matter of the aerial part of the grass and the sorghum were evaluated. The splitting of nitrogen fertilization did not interfere in the yield of sorghum grain straw intercropped with U. brizantha. The intercropping with U. brizantha did not reduce sorghum grain yield. In dry climate conditions in the off-season, inoculation of sorghum seeds cv. Ranchero with A. brasilense increases grain yield.

ABSTRACT One of the alternatives to achieve agriculture with sustainability and reduction in production costs, mainly with fertilizers, is the formation of straw from the previous crop and the use of genus Azospirillum bacteria. The objective of this study was to evaluate the agronomic characteristics and yield of soybean, cultivated in areas under straw of sorghum regrowth inoculated or not with diazotrophic bacteria, single or intercropped with Paiaguás grass under Integrated System of Agricultural Production, in Cerrado region. It was used a complete randomized block design, in a 2 x 2 x 2 factorial arrangement, with four replications, in two agricultural years: with the cultivation of dual-purpose and grain sorghum, single or intercropped with Paiaguás grass, with or without inoculating sorghum seeds with the bacterium Azospirillum brasilense. Soybean production and yield components were evaluated. Inoculation of grain or dual-purpose sorghum seeds with Azospirillum brasilense intercropped with Paiaguás grass, before soybean cultivation, increased the components of production and grain yield of soybean in succession.