| In recent years, all kinds of unreasonable human activities have caused soil and land degradations which seriously threatened the sustainable development of agriculture in China.In North China, multi-tillage system with straw returning including conventional tillage and conservation tillage, reduced tillage and zero tillage, is very important to agricultural sustainable development.This study was implemented in Agricultural Experiment Station of Shandong Agricultural University, based on 13 years of long-term located conversation tillage and residue returning farmland(started in 2002), the effects of conventional tillage, subsoiling,and no-till under different crop residue returned amount on soil organic carbon, CO2 emission,crop photosynthetic characters, and grain yield and qualities were studied under a wheat-maize cropping system.The results showed as follows: residue returning could significantly increase the content of soil organic carbon content, and the soil organic carbon content increased with the increase of residue returned amount. Compared with conventional tillage and zero tillage, subsoiling tillage can not only increase the carbon content in deep soil, but also reduce the mineralization of organic matter, thus, maintained more soil organic carbon.Subsoiling and zero tillage treatment can significantly reduce the total soil CO2 emissions,and zero tillage treatment was the lowest. Residue returning could increase soil CO2 emissions,which was positively correlated with the residue returned amount. The residue not only supply the soil with a large number of carbon source, but also improve the physical properties of soil and increase soil microbial activity, thus increasing soil CO2 emissions. Compared withwhole residue returning, the partial residue incorporation could reduce the soil CO2 emission.Thus, zero tillage with appropriate amount of residue incorporation could effectively reduce the CO2 emission.Subsoiling and zero tillage can increase net photosynthetic rate, stomatal conductance,transpiration rate and chlorophyll content after anthesis of wheat and male tetrad stage of maize, when compared with conventional tillage. The intercellular CO2 concentration under subsoiling and zero tillage was lower than that of the conventional tillage. In the late period of crop growth, leaf chlorophyll contents under subsoiling and zero tillage were higher than conventional tillage. There was a positive correlation between the net photosynthetic rate and the residue returned amount. These results suggest that subsoiling and zero tillage with residue returned can significantly improve crop photosynthetic capacity, delay crop senescence at late growth stage, and increase dry matter accumulation.Subsoiling and zero tillage with residue returning can significantly improve the grain weight of winter wheat, effective panicle number and grain number per spike. Subsoiling treatment got the highest yield among different tillage systems, 1m stubble returned had higher wheat spike number, grain number per spike and yield, when compared with other residue returned amount. Thus, the yield of the S-1 treatment of was the highest. The effects of subsoiling, zero tillage and conventional tillage treatments on the grain weight and grain number per 1000 grain weight of maize were not significant, but 1m stubble returned had the highest yield as compared to other residue returned amount.The contents of DNF and ADF in straw were significantly decreased with the increase of the height from the ground. The contents of DNF and ADF in the residue above 1 m was the lowest, which was about 28% of the total biomass of the whole plant. The content of CP in straw was increased with the increase of the distance from the ground. Thus, the residue above 1 m can be used for forage with higher CP and nutrients contents but lower NDF and ADF contents. |
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