Soil acidification and basic cation use efficiency in an integrated no-till crop–livestock system under different grazing intensities

Under integrated crop–livestock production system (ICLS), the animal acts as a catalyzer, modifying and accelerating fluxes by ingesting forage nutrients (grazing) and returning them to the soil as urine and dung in a continuous process whose magnitude and direction depend on grazing intensity. Thus, ICLS may change soil acidification processes and rates. The objective of this research was to verify the influence of grazing intensities on soil acidification through measurements of the soil chemical attributes in the soil profile and the efficiency of basic cation use in a soybean–beef cattle integration system nine years after surface liming under long-term no-till conditions in southern Brazil. An experiment established in 2001 in a Rhodic Hapludox with soybean (summer) and a mix of black oat + Italian ryegrass (winter) succession was used. Treatments consisted of different grazing intensities during the winter season: intensive grazing (IG), moderate grazing (MG), and no-grazing (NG). The experiment was set up in a randomized complete blocks design with three replicates. To evaluate soil chemical attributes, soil was sampled up to 40 cm, in May 2010, nine years after lime application. To quantify basic cations budgets and efficiencies, the inputs and outputs of calcium, magnesium, and potassium, as well as their initial and final exchangeable soil stocks were evaluated. Areas under grazed treatments, regardless of the intensity (IG or MG), presented lower soil acidification. Calcium and magnesium budgets were negative under NG and positive under MG. Potassium budgets were always negative, regardless of the management system, due to soybean grain harvest exportation and non-productive outputs. The soybean–beef cattle integrated system, with either IG or MG, was more efficient in calcium and magnesium utilization to produce protein; however, grazing does not affect potassium use efficiency.