Effect Of Mulching Methods On Soil Structure Of Aggregate And Soil Carbon Sequestration In Dryland

In recent decades, mulching in the surface was widely used in dryland farming system. The research of measuring the effect of mulching methods on soil physical and chemical properties, aggregate structure and carbon sequestration was important to the global carbon balance and the soil quality. Base on two 6-yr field experiments, we explored the effects of straw mulching and plastic film mulching on soil physical and chemical properties, soil aggregates and organic carbon under dryland farming system. Four treatments were included as the control without mulching, high wheat straw mulching at a rate of 9000 kg/hm2, low straw wheat mulching at a rate of 4500 kg/hm2 and plastic film mulching for winter wheat field. Three treatments were included as the control without mulching, corn straw mulching at a rate of 9000 kg/hm2 and plastic film mulching for the corn field. We take the 6 years mulching experiment as the research object of the research which was located in Changwu Agriecological Station of Loess Plateau. The studies was detected the effect of straw and plastic film mulching on basic physical and chemical properties of soil, aggregate and organic carbon distribution in rainfed winter wheat and spring corn fields. Main results as follows:(1) In winter wheat mulching experiment, the contents of soil water content, total nitrogen, alkali solution nitrogen and available phosphorus was greater in straw mulching treatments than in control without mulching treatment in 0?20 cm soil depths. Soil bulk density in straw mulching treatments decreased in 0-20 cm soil depths when compared to that in no mulching treatment. High straw mulching was better than low straw mulching in improving soil quality. Plastic film mulching decreased soil bulk density, but had no effect on soil water content and soil nutrient content. In spring corn mulching experiment, the contents of soil water content, soil total nitrogen, alkali solution nitrogen and available phosphorus were all greater in mulching treatments than in control without mulching. In contrast, soil bulk density in 0?20 cm soil depths decreased significantly after mulching.(2) In both experiments, the mechanical-stable and water-stable aggregates were given priority to the>0.25 mm aggregate, and the content of>0.25 mm water-stable aggregate was significantly lower than that of>0.25 mm mechanical-stable aggregate. In winter wheat mulching experiment, the contents of> 0.25 mm mechanical-stable aggregate and> 0.25 mm water-stable aggregate were greater in straw mulching treatments than in control without mulching in 0-10 cm and in 0-20 cm soil depths, respectively. The content of>0.25 mm mechanical-stable aggregate increased after plastic film mulching in 10-20 cm soil depth. The content of>0.25 mm water-stable aggregate in 0?20 cm soil depths was not significant between plastic film mulching and no mulching treatment. Compared with those without mulching, the values of mean weight diameter (MWD) and geometric mean diameter (GMD) increased, and the destruction rate of soil aggregates (PAD) value decreased after straw and plastic film mulching in 0?10 cm soil depth. The effect on improving soil structure was better for high straw mulching than low straw mulching or plastic film mulching. In spring corn mulching experiment, compared with no mulching, straw and plastic film mulching treatments were conducive to increase the content of>0.25 mm mechanical-stable aggregate in 0-10 cm soil depth and the content of>0.25 mm water-stable aggregate in 0-20 cm soil depths. The values of MWD and GMD greater and PAD value lower in straw mulching than control without mulching in 0-10 cm soil depth. Plastic film mulching also had a certain effect on improving soil aggregate stability but its PAD value was not significantly difference with that without mulching. The content of>0.25 mm water-stable aggregates content was positively correlated with the MWD and GMD value and negatively correlated with PAD value. The content of>0.25 mm water-stable aggregates can be as a reference index to measure soil structure stability.(3) In the winter wheat mulching experiment, compared with no mulching, straw mulching increased soil orgainc carbon content in 0?20 cm soil depths, and the effect of mulching rate was not significant difference. Plastic film mulching had no effect on soil organic carbon content. In the spring corn mulching experiment, soil organic carbon content increased after straw mulching in both 0?10 cm and 10-20 cm soil depths. However, total organic carbon in plastic film mulching treatment tended to decline in 10?20 cm and 20-40 cm soil depth when compared with that in control without mulching. In both winter wheat and spring corn mulching experiments, the organic carbon contents in>0.25 mm aggregates were significant greater than in<0.25 mm aggregates. The contribution of organic carbon in>0.25 mm size aggregates was significantly higher than in<0.25 mm aggregate. Soil organic carbon was mainly stored in macro-aggregates in both soil depths. Straw mulching increased soil organic carbon content in>0.25 mm aggregates in 0-10 cm soil depth, however, plastic film mulching had no effects on this side. In winter wheat mulching experiment, straw and plastic film mulching had no influence on the organic carbon content in<0.25 mm aggregate. However, the organic carbon in<0.25 mm aggregates was greater in straw mulching than in control without mulching in spring corn mulching experiment. Straw mulching increased the contribution of soil macro-aggregates to soil total organic carbon in 0?10 cm soil depth when compared with control without mulching and plastic film mulching.