Unravelling the chemical and biochemical responses in the rhizosphere of corn after 17 years of pig slurry application

Understanding the chemical and biological processes in the corn rhizosphere that govern nitrogen (N) availability can improve fertilizer management strategies, such as pig slurry (PS) application, in no-till systems on subtropical soils. This study aimed to assess changes in soil chemical properties and microbial activity associated with N availability in the rhizosphere of corn grown in an area with a 17-year history of PS and mineral fertilizer (MF) use. The study was conducted in a long-term field experiment (2004–2021) in southern Brazil, with treatments consisting of PS, MF, and a no-fertilizer control. Rhizospheric and non-rhizospheric (bulk) soils were sampled during the 2019/20 and 2020/21 growing seasons. Soil samples were analyzed for urease and β-glucosidase activities, microbial biomass carbon (C) and nitrogen (N), total organic carbon (TOC), total N (TN), and pH. Long-term PS application enhanced N availability and improved soil quality in the rhizosphere compared with MF alone. PS increased TOC and enzyme activity, particularly β-glucosidase activity in rhizospheric soil, which may facilitate N release to plants. These improvements were associated with increased crop yiels, despite rhizospheric soil pH remaining similar to that of the control treatment. PS also elevated microbial biomass C and N and urease activity, especially in the rhizosphere, although these responses were not directly associated with higher yields. Nevertheless, enhanced N availability in the rhizosphere was evident. These findings suggest that PS application may be a viable strategy for improving soil microbial activity and nutrient cycling in corn production systems under long-term no-till management.