Avaliação da saúde do solo em sistemas agrícolas sob agricultura conservacionista no Brasil

Abstract

Conservation agriculture (CA) has been promoted as the main strategy to regenerate soil life but its effect on soil enzyme activity and on soil microbiota remains little documented. This study investigated the β-glucosidase and arylsulfatase enzymes as tools to evaluate soil health at the field level and through the characterization of soil DNA, we sought to identify the relationship between the microbiome and the different yield environments (YEs) within a production field. Croplands in four main grain-producing states in Brazil, located in the main agro-ecoregions were selected for this study. In each cropland, three environments (high yield (HYE), medium yield (MYE), and low yield (LYE)) were delineated for soil sampling to determine soil chemical attributes and enzyme activity. In one of these fields with a large temporal database, soil DNA characterization was also undertaken. The two soil enzymes investigated were affected by a range of soil attributes and the most important of these were identified, where fine soil particles (clay and silt), high CEC, high Ca2+ content, high Ca2+/Mg2+ ratio, high TOC, TN and SOM were promoters of enzyme activity, on the other hand, soil pH in water (>6.5), high sand content, high P content concentrated in the surface layer, high temperature, low availability of Cu2+ and Mn2+ reduced the activity of these enzymes. Around 40% of the data points sampled had low soil organic matter content; these were associated with low enzyme activity. Furthermore, in HYE there was more biodiversity and a higher presence of plant-growth promoters (Bacillus sp., Penicillium sp., Trichoderma sp., Pseudomonas sp., Bradyrhizobium sp. and Rhizobium sp.), while in LYE there were more plant pathogenic organisms (Fusarium sp. e Macrophomina sp.). The activity of β-glucosidase and arylsulfatase enzymes were efficient indicators of soil biodiversity under CA. Furthermore, the activity of these enzymes serves as an efficient tool to distinguish environments of low productive potential in relation to environments of high productive potential within the fields. It is concluded that the application of the three integrated CA principles focusing on crop rotation and cover crops in the cropping system, results in improved soil health and crop productivity. The main drivers of this soil health regeneration process are restoration of soil organic matter and total nitrogen content through crop diversification, calibrated correction of plant nutrients with fertilization that focuses on increasing Ca2+ content, prevent soil compaction and encourage the growth of plant roots that will support plant growth-promoting microorganisms and a diverse community of soil biota.