Denitrification with different sizes of soil aggregates obtained from dry-sieving and from sieving with water

Abstract

The spatial variability of denitrification in soil was studied further by comparing dry-sieved and wetsieved aggregates of different sizes. It was observed that the denitrification rate generally decreased as the drysieved aggregate size increased. In contrast, the denitrification rate increased as the wet-sieved aggregate size increased. In both cases, however, the denitrification rate was positively related to aerobically mineralizable C. Oven-warming of the wet-sieved aggregates at 105°C for 30 min increased the denitrification rate, apparently due to the release of C substrate. Nevertheless, the positive relationship between the denitrification rate and the wetsieved aggregate size persisted. There was no clear relationship between water-soluble C and the denitrification rate. There may have been a contribution from C in microbial polysaccharides in aggregates of different sizes. The results demonstrated that there was a large spatial variability in denitrification over short distances in soil, which was associated with aggregates of different sizes and water stability.