Tillage effects on soil aggregation, organic carbon fractions and grain yield in Eum-Orthic Anthrosol of a winter wheat-maize double-cropping system, Northwest China

Conservation tillage has been applied in vast semi-arid regions of the Guanzhong Plain, Northwest China. The tillage effects on soil aggregation, organic carbon (OC) stabilization and grain yield on this plain have not been fully elucidated. A 9-year field experiment was established from 2002 on a silty clay loam soil (Eum-Orthic Anthrosol) growing winter wheat-maize in a double-cropping system. Six conservation tillage treatments were applied by different combinations of rotary tillage (RT), subsoiling (SS) and no-till (NT), with or without finely chopped straw retention. Conventional tillage (CT) acted as the control. Results showed that in the surface (0-10cm) soil, the proportion of water-stable aggregates (WSA) <0.05mm was 18% less while that for WSA >2mm was 98% more under NT treatments compared with CT. Additionally, the oxidizable OC content in WSA 0.25-2mm was 27% greater under NT treatments compared with CT. The OC stocks increased under SS by 17%, RT by 16% and NT by 15% relative to CT. Grain yield (wheat + maize) showed similar increasing trends in all the tillage treatments compared with CT. Both OC stocks and grain yield were larger in treatments with than without straw retentions. These results indicate that NT is beneficial for OC accumulation in WSA but is limited in its ability to improve soil structure in this region. SS plus straw retention (fine-chopped or as a mulch) is an effective practice to improve soil structural stability, OC accumulation and soil productivity of Eum-Orthic Anthrosols in Northwest China.