Microbiota do solo, a força motriz para uma agricultura sustentável em sistemas integrados de produção agropecuária: perspectivas sobre estratégias de adubação e de pastejo na saúde do solo e na produtividade da soja

Abstract

The growing demand for food and the need to reduce environmental impact has posed significant challenges to modern agriculture. Therefore, it is essential to improve and implement more conservationist production systems. Integrated Agricultural Production Systems (ICLS) emerge as a promising approach to optimize agricultural production, sustain ecosystems, and promote soil health. Simple changes to management practices within these systems can further benefit soil quality and profitability. Therefore, the objective of this thesis,based on two studies, is to evaluate how different fertilization strategies (Experiment 1) and grazing intensities (Experiment 2) can change soil quality, productivity, and profitability of the system. For this, soil was collected in the cropping phase (soybean, 2021/2022 harvest) from two ICLS experimental protocols (Soybeans in the summer followed by pasture with cattle grazing). The study on fertilization strategies was implemented in Rondonópolis – MT in 2019, it consists of a factorial scheme with two times of fertilization with P and K: in soybeans (Conventional - CF) or in the pasture (System - SF), and two nitrogen fertilization conditionsin the pasture: with (+N) or without (-N). The study on grazing intensities was started in São Miguel das Missões – RS in 2001. This experiment comprises four treatments that differ in grazing height (10, 20, 30, and 40 cm), in addition to a control treatment without animal grazing. In these experiments, we analyzed biochemical (enzymatic activity), chemical (carbon and nutrient content), and biological attributes of the soil (microbial respiration, 16S gene, and ITS,network analyses), in addition to soybean grain productivity, forage, and profitability. The study of fertilization strategies demonstrates that system fertilization management (SF), with (+N) and without nitrogen fertilization (-N), increases soil microbial and enzymatic activity, available P content, accumulation of forage, stocking rate and animal weight gain, providing greater profitability for ICLS. Conventional fertilization without nitrogen (CF-N) reduces the chemical and biochemical quality of the soil, resulting in an increase in qCO2 and a decrease in the system's productivity. In both fertilizer management (CF and SF), adding +N in the pasture phase increased grain productivity. However, the highest profitability of ICLS was observed in SF+N, demonstrating that simple management practices can boost agricultural sustainability. The study of grazing intensities demonstrated that the integration of the animal component and the regulation of grazing practices at heights between 20 and 40 cm not only benefits soil health but also positively influences soybean productivity, with a height of 36 cm as the ideal time to achieve such benefits. Furthermore, it was observed that the animal component at a grazing intensity of 30 cm boosted the microbial communities of the soybean rhizosphere, demonstrating how these factors affect soil quality and, consequently, agricultural productivity. These findings have significant implications for improving responsible agriculture, highlighting the importance of production systems that sustainably intensify agricultural and livestock activities.