Soil tillage practices affecting the soil characteristics and yield of winter wheat and summer maize in North China

The North China Plain (NCP) is one of the most intensively farmed agricultural regions in China, with approximately 70% of the total cultivated land being used for an annual double-cropping system of winter wheat and summer maize. Owing to the long-term rotary and no tillage practices accompanying with the whole straw of winter wheat and summer maize return to field for several years, soil physical characteristics are gradually changing in terms of the increased soil pan depth, bulk density and content of soil nutrients in the surface soil layer. Improving soil quality by changing the tillage practices might help to maintain crop productivity in this region. An experiment was conducted for the winter wheat-summer maize rotation system in Luancheng County, which represented a high yield region, and in Nanpi County, which represented a medium and low yield region, in the NCP. Four treatments-soil deep tillage (DT), subsoiling (SS), narrow subsoiling (NSS), and rotary tillage (control, CK)-before winter wheat sowing and no tillage before summer maize sowing to all treatments were simultaneously conducted at the two areas. Soil bulk density, crop root growth, soil water use, yield and water use efficiency (WUE) were monitored throughout. Results showed that the effects of different tillage practices on soil and crop were different in the two regions. At Nanpi, deep tillage and subsoiling significantly increased crop yield. Compared with traditional rotary tillage, winter wheat yield was improved by 16.5% under DT, 19.3% under SS, and 13.1% under NSS. Yield of summer maize was increased by 17.3%, 16.2%, and 21.9%, respectively, with annual yield increases of 16.9%, 17.6% and 17.8%, respectively. Yield differences were not observed among the DT, SS, and NSS treatments. However, no significant difference in crop yield among the four treatments was found at Luancheng. Furthermore, four tillage practices reduced soil penetration resistance and bulk density for the 0-20-cm soil layer in both Luancheng and Nanpi. At Nanpi, after sowing winter wheat, the soil penetration resistance of the 0-20-cm soil layer under DT, SS, NSS and CK decreased by 69.7%, 72.7%, 72.5% and 68.2%, respectively. At Luancheng, soil penetration resistance of the 0-20-cm soil layer was reduced by 88.8% averagely under treatments of deep tillage and subsoiling, and slightly increased by 7.7% under CK. Soil bulk density of the 0-40-cm soil layer under the four tillage treatments were all lower at wheat harvest compared with that before tillage. Until the summer maize harvest, soil bulk density under different tillage treatments was essentially similar to that before tillage, and there was no significant difference among the four tillage treatments. At Nanpi, WUE of winter wheat and summer maize was significantly increased under DT, SS, and NSS compared with that under CK. At Luancheng, the WUE of winter wheat and summer maize was similar among the four treatments. These results indicated that different tillage practices in the low yield regions benefited crop production and water productivity. However, in the high yield regions, the three tillage practices did not enhance crop performance compared with traditional tillage practice. Therefore, it is suggested that the model of soil rotary tillage can be continuously implemented in the high yield regions of the NCP, whereas DT can be beneficially implemented in the medium and low yield regions.