Short-term sequestration of slurry-derived carbon and nitrogen in temperate grassland soil as assessed by C-13 and N-15 natural abundance measurements

Land application of animal wastes from intensive grassland farming has caus ed growing environmental problems during the last decade. This study aimed to elucidate the short-term sequestration of slurry-derived C and N in a te mperate grassland soil (Southwest England) using natural abundance C-13 and N-15 stable isotope techniques. Slurry was collected from cows fed either on perennial ryegrass (C3) or maize (C4) silages. 50 m(3) ha(-1) of each of the obtained C3 or C4 slurries (delta C-13 = -30.7 and -21.3 parts per tho usand, delta N-15 = +12.2 and + 13.8 parts per thousand, respectively) were applied to a C3 soil with VC and VN values of -30.0 +/- 0.2 parts per thou sand and + 4.9 +/- 0.3 parts per thousand, respectively. Triplicate soil sa mples were taken from 0-2, 2-7.5, and 7.5-15 cm soil depth 90 and 10 days b efore, at 2 and 12 h, as well as at 1, 2, 4, 7, and 14 days after slurry ap plication and analyzed for total C, N, C-13, and delta N-15. No significant differences in soil C and N content were observed following slurry applica tion using conventional C and N analysis techniques. However, natural abund ance C-13 and N-15 isotope analysis allowed for a sensitive temporal quanti fication of the slurry-derived C and N sequestration in the grassland soil. Our results showed that within 12 hours more than one-third of the applied slurry C was found in the uppermost soil layer (0-2 cm), decreasing to 18% after 2 days, but subsequently increasing to 36% after 2 weeks. The tentat ive estimate of slurry-derived N in the soil suggested a decrease from 50% 2 hours after slurry application to only 26% after 2 weeks, assuming that t he increase in delta N-15 of the slurry plots compared to the control is pr oportional to the amount of slurry-incorporated N. We conclude that the nat ural abundance tracer technique can provide a rapid new clue to the fate of slurry in agricultural C and N budgets, which is important for environment al impacts, farm waste management, and climate change studies.