Effects Of Tillage Methods And Straw Cover On Water Erosion Of Lucerne And Wheat Fields

The effects on soil erosion, soil bulk density, soil infiltration, soil compaction, soil aggregation and soil organic carbon under different tillage methods and straw cover rate in lucerne and wheat field had been studied in Dingxi as a typical semi arid area of loess plateau. The main results are summed up as below: 1. Effects of different tillage methods and straw cover rate on soil water erosion 1) Effects of different tillage methods on soil water erosion The infiltration of lucerne and wheat field was descended after ploughed,because Lucerne field with no till was cultivated lucerne long term ,so its capability of rainfall accept was stronger ,and its utilization of natural rainfall was high,so the pounding time and runoff time was delayed .Pounding time and runoff time of spring wheat field with no till(T4) was the fastest, the average was 3.83min and 6.01min respectively. Pounding time of different tillage methods had not significant difference .Pounding time of lucerne field with till(T1) is the longest ,which was 5.22min.Runoff time of lucerne field with no till(T2) was the longest ,which was 11.13min,which was significantly higher than three treatments. 2) Effects of different straw cover rate on soil water erosion Soil surface covering delayed pounding time and runoff time, and the capability of rainfall infiltration of surface soil was improved, the runoff of surface soil was reduced, because the chance of soil were attacked were reduced by covering, so the soil crust did not form. The soil accept more rainwater in rain season, it can offer better soil environment for crop. The pounding time and runoff time of lucerne field with till(T1) was the longest in 50% straw cover , the pounding time and runoff time was 8.79min and 11.83min respectively,it had significant difference compare to that of lucerne field with till and no straw cover. The runoff time of lucerne field with no till and 100% straw cover(T2) was the longest, which was 14.65min,which had significant difference compare to lucerne field with no till and no straw cover. The cumulated runoff of lucerne field with till and no straw cover (T1)was the highest , which had significant difference compared to lucerne field with no till(T2) and spring wheat field with no till(T4).The cumulated sediment of lucerne field with no till and no straw cover(T2) was the lowest. Cumulated runoff and sediment of treatments decreased with the quantity of straw cover increased, but the cumulated infiltration increased in the same time. 2. Effects of different tillage methods on soil infiltration and soil bulk density The soil of long-term cultivate lucerne was ploughed 3 years before rainfall, though the saturated hydraulic conductivity and sorptivity of lucerne field with till(T1) and lucerne field with no till(T2) was higher than that of spring wheat field with till(T3) and spring wheat field with no till(T4), but had no significant difference. The saturated hydraulic conductivity and sorptivity of soil decreased after rainfall simulation. But the saturated hydraulic conductivity of lucerne field decreased was slower than that of spring wheat field. The soil bulk density of surface 0-5cm ploughed was lower than which of no till. The surface soil bulk density of lucerne field with no till(T2) was higher significantly than that of spring wheat field with till(T3). The surface soil bulk density of spring wheat field with no till(T4) was lower than that of lucerne field with no till(T2),but not significantly. 3. Effects of different tillage methods on soil surface structure and soil organic carbon The percent of microaggregates,silt and clay contents of soil aggregates was higher in the ploughed soil and long-term luncerne cultivated soil. In 0-5cm layer, the water stability macroaggregates which was higher than 0.25mm contents of lucerne field with no till(T2) and spring wheat field with till(T3) were 36.1% and 16.7% respectively. In 0-20cm layer, the soil compaction of lucerne field with no till(T2) was higher than that of spring wheat field with till(T3) significantly. In 20-40cm layer, the soil compaction of tillage treatments was higher than that of no tillage. In 0-5cm layer, the total organic carbon of lucerne field with no till(T2) was 15.38 g·kg-1,which was higher than that of other three treatments.