Soil nutrients and microbial community resistant to patch‐burn grazing in southwestern North Dakota

Abstract

Patch‐burn grazing uses the interactive effects of prescribed fire and herbivory to increase heterogeneity in aboveground ecosystem properties. Understanding how management that targets aboveground heterogeneity translates to soil properties and processes provides an important whole‐system context for practitioners. In this study, we investigated how the combination of patch‐burning and livestock grazing aligned with soil nutrients, decomposition activity, and microbial abundance and composition on semi‐arid post‐Conservation Reserve Program rangelands in southwestern North Dakota. We collected soil samples during the 2018–2020 summer grazing seasons in three patch‐burn pastures grazed by cow‐calf pairs and three patch‐burn pastures grazed by sheep. In each year, we measured ammonium, nitrate, calcium, magnesium, phosphorus, potassium, total carbon, and total nitrogen. In 2019 and 2020, we measured soil moisture, decomposition activity, and microbial abundance and community composition. We tested for differences between patches with varying time since fire, between grazer type, and between ecological sites using mixed‐effect models with Tukey post hoc tests and ordinations with post hoc factor and vector fitting. There were no significant differences in any properties between cattle and sheep pastures. Measured nutrients and microbial abundances were not lower in recently burned patches than not yet burned or patches with three years since fire. Bacterial groups comprised the largest proportion of the microbial community across years, ecological sites, and times since fire. Soil moisture, calcium, phosphorus, potassium, total carbon, total carbon:nitrogen ratio, time since fire, and ecological site were significantly correlated with microbial community composition. The lack of negative responses in soil biota and properties under patch‐burn grazing is promising for the continued use of these disturbances in low diversity rangelands.