Bovine urine inhibits microbial function and increases urea turnover in dairy grazed soils

Abstract

Effects of bovine urine on microbial functional attributes within the carbon (C) cycle have not previously been investigated. The magnitude of urine effects on microbial populations may be mediated by the ability of a soil to buffer changes to pH and electrical conductivity (EC) in response to urine. We examined changes in the metabolism of C substrates by microbial communities subsequent to treatment with dairy cow urine in 27 dairy grazed soils across four soil orders. Untreated soils (baseline) and soil treated with urine or water were incubated (25°C) for 21 days then assessed for microbial function using MicroResp™. Urine addition decreased functional capacity, microbial diversity, and microbial biomass C at 21 days after urine addition, but did not affect basal respiration, compared with the water control. Urine addition also led to a shift in community-level physiological profiles. There were no indirect effects of soil pH or EC buffering capacity on the functional microbial parameters measured. Urine addition increased the utilisation of urea and may be a factor in losses of fertiliser nitrogen in dairy systems. The length of time that urine depresses catabolic function could have important implications for long-term soil organic matter cycling under urine patches.