Species and functional diversity of cool-season pastures are influenced by warm-season grazing management

Abstract

CONTEXTIn southern Brazil, livestock producers often overseed cool-season annual grasses into warm-season perennial pastures to extend the grazing season and improve animal performance. However, the effects of warm-season pasture management on the subsequent cool-season pasture are poorly understood. OBJECTIVEWe aimed to evaluate how grazing height and nitrogen (N) fertilization applied to a mixed-species pasture during the warm season affect forage accumulation and diversity in the cool-season pastures. METHODSThe experiment was conducted in a subtropical climate and consisted of two phases: warm season (November/December – April/May) and cool season (May – October/November). During the warm season, we applied a factorial combination of two pre-grazing heights (0.17 and 0.23 m) and three N rates (50, 150, and 250 kg N ha−1) to a mixed-species pasture. During the cool season, we managed all plots equally and measured forage accumulation and diversity using Simpson's and Rao's indices. RESULTS AND CONCLUSIONSWe found that warm-season N fertilization had no residual effect on cool-season pasture responses, but grazing at 0.17 m height during the warm season resulted in higher forage accumulation during the cool season than grazing at 0.23 m height (5100 vs. 4780 kg DM ha−1). However, grazing at 0.23 m height during the warm season increased species diversity (Simpson's index of 0.49 vs. 0.40) and functional diversity (Rao's index of 0.33 vs. 0.29) during the cool season compared to grazing at 0.17 m height. SIGNIFICANCEThis study provides novel insights into the long-term effects of warm-season pasture management on cool-season pasture diversity and productivity in a subtropical climate. It shows that grazing at a height close to the critical leaf area index during the warm season can increase legume proportion and functional diversity in the cool season, which can improve pasture resilience and sustainability. While this study offers valuable insights, it is important to acknowledge its restriction to a single location, and the need to assess the hypothesis raised here to other sites and conditions.