Changes in Dry Matter and Carbon, Nitrogen, and Sulfur Stocks after Applications of Increasing Doses of Pig Slurry to Soils with Tifton-85 for Six Years in Southern Brazil

Pig slurry (PS) has been used as soil fertilizer due to its nutrient and organic matter contents, which may improve soil nitrogen, carbon, and sulfur stocks. The objective of this work was to evaluate the best PS dose that favors the increase in dry matter production and carbon (C), nitrogen (N), and sulfur (S) contents and stocks after applications of PS to soils with Tifton-85 for six years. The experiment was conducted in a randomized block design with four replications, in a hay-producing area under a clayey Typic Hapludox in southern Brazil. The treatments consisted of annual applications of organic and mineral fertilizers at rates based on their N contents, using PS (100, 200, 300, and 400 kg ha−1) and urea (200 kg ha−1), and a control without N application. Samples of the soil in 0–5, 5–10, and 10–30 cm layers were collected in March 2019 and evaluated for soil bulk density and N, C, and S contents and stocks. The Tifton-85 dry matter production was evaluated using samples from three cuts carried out between 2012/2013 and 2017/2018 agricultural years. The applications of increasing doses of PS in Tifton-85 pastures over six years increase linearly the dry matter and soil organic C, N, and S stocks in the 0–30 cm layer. The PS rate equivalent to 100 or 200 kg ha−1 of N is recommended for increasing soil C, N, and S stocks, since it resulted in C, N, and S stocks equal to or higher than the control and mineral (urea) treatments