Nine-year impact of grazing management on soil acidity and aluminum speciation and fractionation in a long-term no-till integrated crop-livestock system in the subtropics

Abstract

Integrated crop-livestock systems (ICLS) can be an option for agricultural sustainability in subtropics. Despite numerous studies evaluating ICLS, there have been limited investigations of aluminum (Al) dynamics in such systems. In this context, this study was conducted in 2001–2010 on Rhodic Hapludox soil with the objective of assessing the impacts of time and grazing on soil acidity and Al fractions (solid phase) and species (liquid phase) in ICLS (soybean-beef cattle) managed with a long-term no-till system. The crop succession consisted of soybean cultivation during summer and a mix of black oat + Italian ryegrass during winter. Treatments consisted of different grazing managements during the winter season: intensive grazing, moderate grazing, and no-grazing. For this study, sampling was performed prior to the first and after nine grazing seasons. Lime was applied to the surface of the entire study area immediately after the first grazing season. We demonstrated differences in the Al forms in the soil solid and liquid phases over time and with different managements. The ICLS with intensive grazing or moderate grazing during the winter season led to a lower availability of total Al in the soil solution and a higher base saturation and lower Al saturation in the soil solid phase compared to non-grazed areas. However, the soil pH is similar between grazed and non-grazed. Despite such differentiated dynamics, the carbon accumulated in the soil with a long-term no-till management guarantees that the preponderant Al form is linked to organic compounds, maintaining the content of phytotoxic species and the Al3+ activity below the critical limit for plant growth.