Temporal variability drives soil chemical and biological dynamics more than grazing in a northern mixed-grass prairie

Abstract

Quantification of soil health dynamics relative to grazing can inform both agriculture and conservation. We conducted an experiment near Lingle, Wyoming, USA, on a semi-arid northern mixed-grass prairie from 2017-2019. Three grazing density treatments (NG - not grazed; MRG - moderate rotationally grazed a herd of 4 Angus heifers, and UHD - ultra-high density rotationally grazed a herd of 33 Angus cow-calf pairs) were replicated four times in a randomised complete block design across twelve - 0.405 ha paddocks. Soil sampling was conducted prior to grazing in June 2017, one-week post grazing in July 2019, and six weeks post grazing in August 2019 and included a suite of forage, ground cover, soil chemical, soil physical, and soil microbiological measurements. Grazing treatment did result in lower vegetation structure but had no effect on any soil variables (P > 0.05). Conversely, the sampling interval was more influential for predicting fluctuations in chemical (15 variables significantly different within at least one treatment) or microbiological (13 variables significantly different within at least one treatment) variables than grazing treatment. The study was conducted in an intact native prairie with initial and final values indicating "Very Good" soil health, including the saturated:unsaturated fatty acid ratio, an indicator of stress.

Keywords

• grazing intensification
• ecosystem
• animal density
• beef
• grassland
• rangeland