Rangeland application of biochar and rotational grazing interact to influence soil and plant nutrient dynamics

Abstract

Few studies have been conducted to evaluate the use of wood biochar in temperate rangeland ecosystems and none have investigated the interactive influence of wood biochar and cattle trampling activity (associated with short-term rotational grazing) on soils and plants. We conducted a field study on a semi-natural pasture in western Montana, USA to evaluate how wood biochar, with or without short-term intensive trampling affected biochar incorporation depth, soil physicochemical properties, nutrient dynamics, and grass nutrient concentrations with a particular focus on nitrogen (N) and phosphorus (P). We hypothesized that cattle trampling alone would induce soil compaction and generally reduce soil nutrient cycling rates and/or availability, but the presence of biochar prior to trampling could improve soil aeration and grass nutrition. After three months, we found that trampling alone significantly increased surface soil bulk density and reduced the values of nearly all soil N metrics examined in this study; however, the application of biochar prior to trampling improved infiltration rate and increased net nitrification. Trampling also facilitated biochar incorporation into soils. Biochar additions significantly increased soil available organic P (i.e., enzyme extractable P) while reducing soil inorganic P (i.e., CaCl2-P, citrate-P) with or without trampling. Soil P responses appeared to be associated with biochar ortho-P sorption capacity and was more pronounced in soils that had undergone cattle trampling. Changes in soil P were reflected in grass P concentration after three months. Overall, our field study demonstrated that the use of biochar on rangeland soils with short-term rotational grazing could result in a neutral to positive effect on soil and plant nutrients.