Assessing the physical quality of subsoiled cohesive horizons for Eucalyptus plantation

In Brazil, Eucalyptus plantations occupy approximately 7.6 million hectares, of which 8% are located in the state of Bahia. In southern Bahia, these plantations are predominantly established on soils with cohesive horizons, characterized by high soil strength when dry and restricted pore connectivity when wet. These conditions reduce water, air, and nutrient fluxes, adversely affecting root development and plant growth. Subsoiling is a management practice commonly employed to mitigate these limitations; however, its effectiveness and persistence in modifying the physical attributes of naturally dense soils remain under debate. This study aimed to assess the effects of subsoiling on the physical quality of cohesive Argissolo Amarelo under Eucalyptus cultivation. Two sites were evaluated: one with Argissolo Amarelo distrófico típico (PA1) and another with Argissolo Amarelo distrocoeso fragipânico (PA2), both subsoiled to 0.60 m prior to planting. Soil samples were collected 6.5 years after planting in PA1 and 1 year after planting in PA2. Sampling was performed in the planting rows (0.20–0.25, 0.35–0.40, and 0.60–0.65 m) and the inter-rows (0.20–0.25 m). The following physical attributes were determined: bulk density, total porosity, the least limiting water range (LLWR), the water retention curve and the pore size distribution. According to the results, subsoiling led to sustained improvements in soil physical quality. The subsoiled layers exhibited lower bulk density, increased macroporosity, and a higher LLWR. Additionally, pore distribution was altered, with a higher proportion of cryptopores in non-subsoiled layers. The surface layers showed greater water retention at high matric potentials in the planting rows and low potentials in the inter-rows. These findings underscore the potential of subsoiling to enhance the physical functionality of cohesive soils under Eucalyptus, with effects that persist for multiple years post-subsoiling.