Soil structure and its influence on microbial biomass in different soil and crop management systems

Abstract

Methods for assessment of soil structure in the field are useful for determining the sensitivity of soil to different management systems. Soil and crop management have a fundamental role in the maintenance and improvement of soil quality, as they have a direct influence its structure and on microbiota habitats. The aim of this study was to qualify and quantify homogeneous morphological units (HMUs) in a dystroferric Red Latosol, in a 22-year experiment with treatments consisting of a no-tillage planting system (NT), no-tillage with chiseling every 3 years (NTC) and conventional tillage (CT), using crop rotation (CR) [with five different crop species in 3 years] and succession systems (CS) [only two crop species]. The NT and NTC treatments presented HMUs with a continuous and cohesive structure and increased visible porosity at the surface, and continuous and cohesive units with lower porosity below this layer. The surface layer of the NT treatment presented free units made up of small and medium sized clods, and below this layer, compact, continuous units with little porosity. The soil management systems with crop rotation presented less compact units and roots with fewer morphological deformities than in the treatments with succession systems. Significantly higher levels of carbon and nitrogen microbial biomass (CMB and NMB) were observed in the HMUs in NT and NTC systems under both crop rotation and succession systems, and these had higher visible porosity than the units found in the CT system. On average, HMUs in the NT and NTC treatments presented 20% more CMB and 51% more NMB than in the CT treatment. NMB was the parameter most highly affected by the soil management. At depths of 0–20cm, total organic carbon (TOC), was higher by an average of 21% than in the NT and NTC treatments. Total nitrogen (TN) was also affected by the soil management, increasing by an average of 50% in the NT and NTC treatments. This demonstrates how the tillage of the soil exposes the organic matter in the aggregates to oxidation and nitrogen mineralization.