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

Land application of animal wastes from intensive grassland farming has caused growing environmental problems during the last decade. This study aimed to elucidate the short-term sequestration of slurry-derived C and N in a temperate 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 thousand, 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 thousand and + 4.9 +/- 0.3 parts per thousand, respectively. Triplicate soil samples were taken from 0-2, 2-7.5, and 7.5-15 cm soil depth 90 and 10 days before, at 2 and 12 h, as well as at 1, 2, 4, 7, and 14 days after slurry application 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 application using conventional C and N analysis techniques. However, natural abundance C-13 and N-15 isotope analysis allowed for a sensitive temporal quantification 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 tentative 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 the increase in delta N-15 of the slurry plots compared to the control is proportional to the amount of slurry-incorporated N. We conclude that the natural abundance tracer technique can provide a rapid new clue to the fate of slurry in agricultural C and N budgets, which is important for environmental impacts, farm waste management, and climate change studies.