The influence of a year-round tillage and residue management model on soil N fractions in a wheat-maize cropping system in central China.

Tillage practice and residue management play important roles in N pool in soils. This study determined the impacts of tillage practice and residue management on crop yield. It also investigated the distribution, fractionation, and stratification of N at soil at depths ranging from 0 to 60 cm under wheat-maize cropping systems. Three treatments were established in 2009: no-tillage with straw removal for winter wheat and summer maize (NT), no-tillage with straw mulching for winter wheat and summer maize (NTS), no-tillage with straw mulching for summer maize and plow tillage with straw incorporation for winter wheat (NPTS). After 8 years, soil total nitrogen (TN) content in NTS was greater than in NT, but only in 0-10 cm layer. NPTS treatment increased TN content over NT and NTS in 10-20 cm layer by 18.0% and 13.9%, and by 16.8% and 18.1% in 20-30 cm layer, respectively. Particulate organic N, microbial biomass N and water-extractable organic N levels were the greatest in 0-10 cm layer under NTS treatment; and in 10-30 cm layer, the corresponding values were the highest under NPTS treatment. NPTS treatment could immobilize the mineral N in 10-30 cm layer, and reduced leaching losses into deeper soil layers (40-60 cm). Furthermore, total yield increased by 14.7% and 8.5% in NPTS treatment compared to NT and NTS treatments, respectively. These results indicate that NPTS is an effective and sustainable management practice, which will improve soil fertility, sustainable crop production, and environmental quality in low-productivity soils in central China.