Effect of sheep grazing systems on soil, yield, and species diversity in an agricultural watershed, Nigeria

Intensified grazing pressure and forest conversion to pasture affect biodiversity of the forest-grassland transition zone in Imo River watershed, Nigeria. This study assessed how different grazing systems influence soil properties and plant biodiversity in an intensively managed agricultural watershed. It is hypothesized that plant diversity and richness would decrease substantially with continuous grazing (CG) and heavy grazing whereas rotational grazing (RG) would enhance soil N, C, aboveground net primary production (ANPP), and biodiversity under light grazing. In a research period that covered two seasons (2023 and 2024), vegetation, soil, and climate data were collected. ANOVA was used to determine the differences and effects of the grazing systems on the vegetation parameters. Management systems (P = 0.011) and grazing intensities (P = 0.023) significantly affected the ANPP, NPPdiff (P = 0.045) and RGR (P = 0.000). Similarly, plants’ composition was significantly affected by different management systems (P = 0.016), grazing intensities (P = 0.001), and year (P = 0.035). Soil total N in RG was over 50 % higher than the content in CG and 15 % higher than that under UG. During the specified study seasons, species diversity and richness were over 30 % higher in RG than in CG and UG. In contrast, the specific plant height (SPH) and ANPP values observed in UG were over 40 % larger than those recorded in either RG or CG. Except for the forbs, all the species coverages were at least 10 % higher under light grazing compared to heavy grazing. Consequently, a sustainable grazing system (e.g. RG) with light or moderate stocking rate could increase soil N, plant diversity, and aboveground biomass productivity in Imo watershed. The study could be beneficial to the smallholder farmers and all the stakeholders in food security and production chain, especially in the prevailing climate change.