Aggregation Index and Carbon and Nitrogen Contents in Aggregates of Pasture Soils under Successive Applications of Pig Slurry in Southern Brazil

Abstract

Pig slurry (PS) applications affect soil aggregation and carbon and nitrogen contents in aggregates. The objective of this study was to evaluate changes caused by successive applications of PS and mineral fertilizer on soil aggregation and carbon (C) and nitrogen (N) contents in aggregates of a clayey Typic Hapludox cultivated with Cynodon dactylon cv. Tifton-85 in southern Brazil. The treatments consisted of six annual applications of PS (100, 200, 300, and 400 kg N ha−1) and urea (200 kg N ha−1), and a control with no fertilizer application. Soil samples were collected in March 2019 and evaluated for aggregate stability, through the geometric mean diameter of aggregates (GMD), and GMD sensitivity index (SIGMD), and mass of macro-, meso-, and microaggregates. Total organic carbon and nitrogen contents were determined in macroaggregates and microaggregates. Applications of PS to pasture soils increase dry matter production of Tifton-85 and can increase soil aggregation by increasing the mass of macroaggregates. The highest PS rates decreased aggregate stability, resulting in lower macroaggregate mass, GMD, and SIGMD, and higher microaggregate mass. PS applications to pasture soils can increase C and N contents in macro and microaggregates, and improve soil aggregation when using the rates of 100 or 200 kg N ha−1, mainly in subsurface layers.