Quantification of priming and CO₂ respiration sources following slurry‐C incorporation into two grassland soils with different C content

The fate of incorporated slurry‐C was examined in a laboratory experiment using two UK grassland soils, i.e. a Pelostagnogley (5.1 %C) and a Brown Earth (2.3 %C). C 3 and C 4 slurries were incorporated into these two wet‐sieved (C 3 ) soils (from 4–10 cm depth). Gas samples were collected 0.2, 1, 2, 3, 4, 6, 9, 20, 30 and 40 days after slurry application and analyzed for CO 2 concentration and δ 13 C content. Slurry incorporation into the soil strongly increased soil CO 2 respiration compared with the unamended soil. Total (40 day) cumulative CO 2 flux was higher for the Pelostagnogley than the Brown Earth. The 13 C natural abundance tracer technique enabled quantification of the sources of respired CO 2 and priming effects (days 0–9). Proportionally more slurry‐derived C was respired from the Pelostagnogley (46%) than the Brown Earth (36%). The incorporated slurry‐C was lost twice as fast as the native soil C in both soils. Slurry incorporation induced a priming effect, i.e. additional release of soil‐derived C, most pronounced in the Pelostagnogley (highest C content). The majority of respired soil‐derived C (>70%) was primed C. The study indicated that potential reductions in ammonia volatilisation following slurry injection to grasslands might be negated by enhanced loss of primed soil C (i.e. pollution swapping). Copyright © 2003 John Wiley & Sons, Ltd.