In Huang-Huai-Hai area in China, winter wheat (Triticum aestivum)/summer maize (Zea mays) rotation is the dominant two-crop-per-year cropping system. Crop residue removal and subsoil compaction have become limiting factors for yield improvement in the area. Tillage and crop residue retained are two effective ways to improve soil properties and increase crop yield. Soil tillage and crop residue retained can reduce soil bulk density, improve water storage and aeration in the soil, increase soil microorganism and enzyme activities, improve soil biological properties, thus promote plant root growth and increase crop production. However, studies in the past mainly focused on the effects of single tillage or single crop residue retained on soil respiration. There is a need currently for research in the effects of tillage, crop residue retained and their interaction on soil respiration under the two-crop-per-year cropping system. A two-year field study from 2010 to 2012 was conducted to determine effects of tillage practice and crop residue management on soil respiration, soil temperature, soil water content, soil compaction, soil organic carbon content, dry matter accumulation of plant and root in the wheat-corn double crop cropping system. The study was conducted at the Wen County Experimental Station, Henan, China. The experiment was arranged in a split-plot design with three replications. Tillage practice and crop residue management were two factors of interest. The tillage treatment was randomly assigned to main plots and crop residue treatment was randomly assigned to sub-plots. The tillage practice treatments were: moldboard plough (MP) to a maximum depth of 15 cm, deep moldboard plough (DMP) to a maximum depth of 30 cm, and chisel plough (CP) to a maximum depth of 30 cm. All three tillage treatments were implemented after corn harvested in October of 2010 and 2011. In addition to different plough treatments, all plots were disc harrowed before wheat planting. There were no direct tillage implements for corn as corn was seeded using a no-till planter. Crop residue management included two levels: crop residue retained (CRRet) and crop residue removed (CRRem). For the CRRet treatment, the wheat straw produced in 2011 and 2012 remained in fields as straw mulching for the following no-till corns, and the 2010 and 2011 corn stover was also incorporated into soil by tillage implements. For the CRRem treatment, both wheat straw and corn stover were removed from the field. The results indicated that there were significant (P<0.05) effects of tillage and crop residue management on soil respiration. Both soil tillage and crop residue retained significantly (P<0.05) increased soil respiration. Crop residue retained increased soil respiration during winter wheat season, but decreased soil respiration during summer maize season. During the growth period of winter wheat, DMP and CP increased soil respiration by 31.8% and 21.9%, respectively, relative to MP. The CRRet increased soil respiration by 14.3% compared with CRRem. On average, DMP+CRRet and CP+CRRet treatments increased soil respiration by 45.5% and 38.2%, respectively, as compared with MP+CRRem treatment. During the growth period of summer maize, DMP and CP increased soil respiration by 47.6% and 47.8%, respectively, relative to MP, and CRRet decreased soil respiration by 18.0% compared with CRRem. On average, DMP+CRRet and CP+CRRet treatments increased soil respiration by 19.7% and 22.2%, respectively, compared with MP+CRRem treatment. The soil respiration was significantly positively correlated with soil temperature and soil carbon, while negatively correlated with soil compaction. The correlation coefficient of soil respiration and soil temperature was highest among the correlation coefficients that affected soil respiration. Compared with the MP+CRRem treatment, the dry matter accumulation of the DMP+CRRet and CP+CRRem treatments increased by 34.9% and 38.2%, the root dry weight density increased by 45.0% and 39.4%, respectively. Therefore, we concluded that deep moldboard plough or chisel plough with crop residue retained was the most appropriate tillage practice in Huang-Huai-Hai area.
