Solubilisation of soil carbon following treatment with cow urine under laboratory conditions

Abstract

There have been reported losses of soil carbon (C) under intensively grazed pastures, and soil C solubilisation following cow urine deposition was identified as a possible mechanism. We measured potential soil C solubilisation in pasture and plantation pine soils following treatment of soil with cow urine. Soils from five paired pasture and pine sites were collected. Adsorption of urine-C and desorption of soil C was determined by shaking air-dried soil with cow urine for 4 h at 4°C, decanting the urine, and then extracting the soil with water. Soil C solubilisation was the difference between adsorption of urine-C and desorption of soil C. Solubilisation of soil C in the pine soils including the organic layers was 21.6 ± 2.6 mg/g (10.5 ± 1.1% of soil C concentration), in the pine soils excluding the organic layers 7.5 ± 2.2 mg/g (18.7 ± 5.8%), and in the pasture soils 12.4 ± 5.3 mg/g (27.8 ± 7.3%). There was no significant difference with respect to soil C solubilisation between the pine (with and without organic layers) and pasture soils. Soil C lower in the profile may be as susceptible to solubilisation as C in topsoils. Adsorption of urine-C was minimal. Solubilisation of soil C under urine patches may contribute to losses of soil C under intensively grazed pastures, and this hypothesis would benefit from further testing under field conditions.