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Inoculation forms with Azospirillum brasilense in sorghum intercropped or not with palisade grass and residual effect on soybean: a sustainable nitrogen management tool in low carbon agriculture

Abstract

The insertion and development of integrated agricultural systems, with crops that are more tolerant to high temperatures, water deficit and flexibility in terms of grain and/or forage production, such as sorghum and palisade grass, can be a viable option for optimizing agriculture, mainly in more climatically stressful regions and with sandy textured soils, as in the Nova Alta Paulista region, as long as it is inserted in adequate production systems and associated with technologies that promote greater resilience to them. Nitrogen fertilization is one of the biggest costs in the production process of non-legume crops. Nevertheless, soybean cultivation requires large amounts of N to obtain high yields, despite the fact that a large part of the N in soybean comes from biological nitrogen fixation (BNF). Developing management techniques that minimize the need for chemical application of N, and better use of this nutrient in production systems, is essential for an increasingly sustainable and productive agriculture. Recent research has demonstrated the potential for the use of the Azospirillum brasilense bacterium with a view to increasing the efficiency of use of applied fertilizers and nutrients in the soil, mainly through greater root growth, in addition to a small contribution to BNF, optimizing the management of nutrients and plant growth in production systems. In addition, the sorghum-palisade grass consortium is a technology in which the two species are cultivated together, with the objective of producing grains and sorghum straw and straw or forage, with undeniable benefits for the sustainability of production, especially if considered the climatic unpredictability, typical of agricultural activity. Although several studies have been carried out in recent years on the inoculation of A. brasilense in different plant species, most studies do not focus on the benefits arising from the forms of inoculation associated or not with the sorghum-palisade grass intercropping in the optimization of the sorghum-soybean production system. Thus, studies are needed that focus not only on the benefits of nitrogen fertilization management in the intercropped crops, but also on its residual effect and benefits on soybean. The objective of this proposal is to evaluate ways of inoculation with A. brasilense in sorghum intercropped or not with palisade grass and residual effect on soybean, aiming to optimize the management of nitrogen fertilization in the sorghum-soybean system. The research project will be developed between 2023 and 2025 in the municipality of Dracena - SP, belonging to the Nova Alta Paulista region, in a typical dystrophic Ultisol with a sandy texture. The experiment will be carried out in a randomized block design with four replications, in an 8 × 2 + 1 factorial scheme: inoculation with A. brasilense (inoculation in the seeds, in the sowing furrow, total area and without inoculation, combined with 100% or 75% of the N dose recommended for the sorghum crop) in consortium or not with palisade grass. The potential benefits of inoculation forms associated with the sorghum-palisade grass intercropped will be evaluated in soybean in succession, evaluating the residual effect of the aforementioned treatments. An additional fallow treatment in the second crop (sorghum cultivation) followed by single soybean cultivation will be considered as absolute control. The accumulation of N in sorghum, palisade grass and soybean tissues, the efficiency of use (NUE) and recovery of N applied via fertilizer in sorghum will be determined using the technique of isotopic dilution with 15N. In addition, we intend to evaluate the photosynthetic parameters of gas exchange, water use efficiency (intrinsic and instantaneous) and carboxylation, leaf chlorophyll index, shoot and root dry mass, nodules (soybean), grain yield (sorghum and soybean) and dry matter (palisade grass), as well as the influence of treatments on C and N stocks (total and inorganic (AU)

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