Physical assessment of a Haplohumox soil under integrated crop-livestock system

Abstract

Soil structure characterization in both macro and micro scales is very complex. The soil porous system (SPS) is responsible for numerous functions in soil, such as water infiltration, retention, redistribution, gas exchange, root growth and other processes related to the SPS. Indices, hydraulic functions and micromorphological measures of soil physical quality (SPQ) were carried out to evaluate the structure of a Haplohumox under integrated crop-livestock system (ICLS). Two soil depths were analyzed (0–10 and 10–20 cm) in four tillage systems: conventional tillage (CT), minimum tillage (MT), no-tillage (NT) and chiseled no-tillage (CNT), taking into account the annual ryegrass cropped during the winter for grazing (G) and silage (S) use. Soil water retention curve (SWRC), pore size distribution function (PSD), SPQ indices and the aeration hydraulic-energy function were associated together with other parameters obtained via micromorphological analysis of soil structure. Areal porosity (AP) was determined to classify the shape of pores as rounded (R), elongated (E) and complex (C). The size of pores was chosen based on their function and classified as storage pores (0.5–50 μm), transmission pores (50–500 μm) and fissures (>500 μm). The number of pores (NPo) was also estimated considering the disconnected pores. Results indicated that the top layer is most affected by tillage. Rounded pores were predominant for all evaluated systems, whereas complex pores such as fissures presented the largest contribution to AP at the deeper surface layer for all treatments. The plowing operation affected soil infiltration and water retention processes in MT and CT as well as AP and NPo in the NT system. NT and CNT required less energy to drain water in both surface layers evaluated. In the top layer MT/S yielded the largest energy to release water, exhibiting small values of AP and a homogeneous SPS. Strong correlation was found between absolute aeration index and some shape parameters of PSD, evidencing the physical relation between these indices. The micromorphological analysis supported the understanding of the other SPQ indices and aeration function for the tillage systems evaluated here.