Carbon leaching from undisturbed soil cores treated with dairy cow urine

Abstract

Solubilisation of soil carbon (C) under cow urine patches may lead to losses of soil C by priming or leaching. We investigated the solubilisation and bioavailability of soil C in undisturbed pasture soil treated with urine. We also studied the contribution of acid-neutralising capacity (ANC) forcing and aggregate disruption as mechanisms of soil C solubilisation. Undisturbed soil cores (0–5 cm; Typic Udivitrand) were treated with water or δ¹³C-enriched urine and subsequently leached. Urine deposition increased total C and dissolved organic C leaching by 8 g C m⁻² compared with water. Soil C contributed 28.1 ± 0.9% of the C in the leachate from urine-treated cores (ULeachate). ANC forcing of urine was 11.8 meq L⁻¹ and may have contributed to soil C leaching, but aggregate disruption was unlikely to have contributed. The bioavailability of organic C in ULeachate was four times greater than in both cow urine and water leachate. It is possible that ULeachate may lead to priming of soil C decomposition lower in the profile. Further testing under field conditions would determine the long-term contribution of urine deposition to dissolved organic C leaching and the fate of solubilised C in pastoral soils.