Effect Of Tillage And Straw Returning On Sources Of Soil Organic Carbon In Wheat-Maize Crop System

Conservation tillage technology has many advantages in crop production, and it was gradually promoted in our country from 1970 s. At present, most of the studies have reported their results of tillage and residue returning on soil carbon sequestration, however, there was less report on the carbon resources for different crop residue and their contributions under different tillage and residue returning systems. Using wheat- maize cropping system in North China Plain, the effects of tillage and residue returned on crop and soil organic carbon were analyzed, and suitable tillage method and residue returned amount were analyzed. This paper will provide theoretical and technical supports to high yields of wheat- maize and soil carbon sequestration. The main results were as follows:1 Effects of tillage methods and residue returning amount on yieldCompared with conventional tillage, subsoiling increased the grain number per ear and yield of maize. No-till reduced the grain number per ear and the yield of summer maize. No-till also reduced the number of productive ears, grain number per ear, and 1000-grain weight of wheat. Subsoiling significantly increased the yield of wheat. The effect of residue returned stubble 1 m increased grain yield of maize and wheat significantly. The annual total yields of S-1 was 14.71% higher than CA. The annual total yields of ZA was 6.09% lower than that of CA.2 Effects of tillage methods and residue returning on soil organic carbon amountSoil organic carbon content?SOC? increased with the increment of residue returned amount, and all residue returned has the highest soil organic carbon, but the largest increase occurred in 1 m residue returned treatment, which is 9.32%. SOC decreased with the soil depth. Compared with conventional tillage, no-till and subsoiling increased SOC in soil surface. In the 30?40cm soil layer, the SOC of conventional tillage was significantly higher than no-till and subsoling. SOC increased with the increment of residue returned, but the effect of stubble 1 m returned was better.3 Effects of tillage methods and residue returning on soil ¹³CSoil 13 C increased with soil depth. Compared with conventional tillage, 13 C stratifications of zero tillage and subsoiling were more significant. No-till can significantly increased 13 C in soil surface, however conventional tillage treatment had the highest 13 C in 30-40 cm soil layer. 13 C increased with the increased amount of residue returned, and the biggest increased is maize 1m stubble returning.4 Contribution of wheat and maize residues to soil organic carbonSubsoiling can increase crop residue on the contribution of soil organic carbon co ntent by 17.59% and 17.59% relative to no-till and conventional tillage, respectively. The contribution of winter wheat residue to soil organic carbon in summer increased with the increase of the quantity of maize residue returned, but there was no rules for summer maize residue. Winter wheat residue to soil organic carbon contribution is 1.5 times of that of summer maize residue. At the same time, the contribution of winter wheat residue to soil SOC quantity reduced with the increase of soil depth, but there was no rule for summer maize residue.5 Effects of tillage methods and residue returning on MRT of soil organic carbonIn maize growing season, soil organic carbon retention period was 150-200 days, however in wheat growing season it was about 350 days. In maize growth season, the update rate of soil organic carbon in subsoiling is the fastest, but there were no significant differences for the other three tillage methods. In wheat growing season, the MRT of no-till was lowest. Regardless of maize growing season or wheat growing season, the update rate of soil organic carbon was increased with the increase of residue returned amount. The MRT of soil organic carbon of wheat growing season is 2.18 times of that in maize growing season.6 The residue of summer maize and winter wheat yield and nutritionMaize residue in water content, calcium, potassium, soluble sugar and starch is significantly higher than on wheat residue. Wheat residue calcium, potassium, soluble sugar and starch yield were 22.83%, 3.64%, 44.74 and 22.86% of maize residue, respectively. The crude fat, crude protein and phosphorus production in wheat residue were 178.76%, 183.62% and 126.43% of those in maize residue. The differences on nutritions may promote the activity of soil microorganisms and animals, increase the maize residue decomposition and the transformation from wheat residue.7 CO₂ distribution and sources in summe r maize canopyIn maize canopy,only 16.79% of the CO₂ amount was from soil released. Maize canopy CO₂ in near ear leaves is the minimum, which was 350.27 ppm. In 0-40 cm canopy, CO₂ concentration can up to 478.33 ppm, and 32.40% of CO₂ amount was from soil release. And with the distance to soil surface increased, the proportion of soil CO₂ emissions decreased. In theory, soil release of CO₂ on photosynthetic of maize ear leaf contribution 20.17% in the condition of 1400?mol/m2/s light intensity. In ear leaf photosynthetic CO₂ of air is 3.96 times CO₂ of soil emissions...