A SAÚDE DO SOLO EM PEDOAMBIENTES DE PRODUÇÃO DE SOJA E A SUA RELAÇÃO COM O SISTEMA DE MANEJO

Abstract

Brazilian agricultural activity is consolidating its expansion in the current verticalization focus of production processes and with farms located in the Cerrado Biome adopting the largest number of production technologies in the world. Paradoxically, the development of agricultural systems is increasingly dependent on inputs and, although there are technological bases for the development of conservationist agriculture, many farmers still do not adopt them, which compromises sustainable development even in pedoenvironments with high agronomic performance. This is the subject discussed in this thesis, whose objective was to evaluate soil quality in pedoenvironments for soybean production and the relationship with the management system, evaluating soil quality indicators in depth, on soybean farms, in order to develop an integrated management assessment tool and apply it to the soil characterization aspects of the studied areas, and to evaluate the agricultural impact on the soil physical quality indicators on farms in the Brazilian Cerrado with a view to proposing a tool for diagnosing compaction. In the first chapter, the hypothesis that soil health regulates its functioning within ecosystem limits was tested through processes that are independent but interconnected by the plant component. To this end, soil samples were collected from 40 soybean crops located on farms in the southwest region of the state of Goiás, Brazil, whose agronomic performances exceed the regional, national and major soybean-producing countries' averages worldwide. In these, the chemical attributes of cation exchange capacity (CEC), pH, potassium (K), phosphorus (P) and calcium (Ca) were determined; physical attributes of soil density (Ds), relative density (Dsrel) and granulometry (texture); and biological attributes of enzymatic activity (β-glucosidase) and soil organic matter (SOM); these were classified into chemical, physical, biological and profile edaphic aspects by the association of attributes and layers related to agronomic production. By proposing scoring scales for each indicator, the impact of soil management was assessed in distinct layers and integrated into a soil health index called the profile Soil Quality Index (P-SQI). Nine indicators evaluated estimated this attribute and were representative of the main soil management obstacles faced by farmers. Our results indicated high variability in all indexes evaluated due to the natural heterogeneity of soils in interaction with the practices adopted, with physical problems associated with soil compaction being the greatest agronomic limitations and, consequently, environmental degradation. Regarding soil organic matter, the challenge lies in the necessary storage throughout the profile aiming at agroenvironmental gains, while chemical edaphic aspects expressed the available technologies and farmers' efforts in assessing and correcting soil fertility, with the greatest restrictions associated with P, which most impacts crop production costs. In the second chapter, five more farms with lower performance were added to evaluate the effectiveness of a soil compaction diagnostic tool. The soils were analyzed for characterization and to obtain 12 properties indicating physical quality, which is strongly influenced by texture, and it was necessary to isolate the impacts of soil use and management on soil composition, which was possible by determining the relative density and robustness of soil macroporosity. Thus, it was possible to diagnose the compaction occurrence with 99% accuracy, attested by a binomial test comparing soil structural conditions, and with its occurrence in all production pedoenvironments, in all management systems evaluated and mainly in layers immediately below the surface. While this is not a problem in sandy and medium-textured soils, it is practically inevitable in clayey and particularly very clayey soils and requires efforts by farmers to mitigate it.