Influence of soil moisture and land use history on denitrification end-products

We investigated the effects of recent moisture history on the relative production of N(2)O and N(2) during denitrification in soil from cropped and successional ecosystems. The soils were pedogenically identical but had been managed differently for the past decade. Sieved soils were amended with nitrate, glucose, and water. Long-wet and short-wet incubations received 80 and 0%, respectively, of prescribed water 2 d before incubation and the rest just before incubation. The N(2)O and N(2) production and N(2)O mole fraction (N(2)O/[N(2)O + N(2)]) were measured using acetylene inhibition. The N(2) production and soil IN enrichment were measured by (15)N-gas evolution. The response of N(2)O mole fraction to moisture history differed by ecosystem. Mean N(2)O mole fraction in the successional system was about the same for long-wet and short-wet treatments (0.34 and 0.33, respectively). For the cropped system, however, the N(2)O mole fraction was 0.36 for the long-wet and 0.90 for the short-wet treatment. Thus, in the cropped system a much smaller proportion of end product was N(2)O if soil had been wet for 2 d. For N(2) fluxes, the isotope method gave the same pattern (r = 0.92) but only about one-third the magnitude, suggesting that N(2) derived from two distinct pools. Differences in response of N(2)O mole fraction for successional and cropped soils may be due to differences in microbial communities. Further knowledge of ecosystem differences with respect to N(2)O mole fraction and recent moisture history may improve modeled estimates of local and global N(2)O fluxes.