Effects Of Different Rainfall Intensities And Slope Gradients On Water Conservation Of Straw Mulch

Using indoor artificial rainfall simulation experiments to study the runoff situation in different rainfall intensities and slopes at sloping land. Revealing the mechanism of straw mulch water conservation, the rules of sloping erosion with rainfall intensities and slopes changed on purple soil. There are the main ideas:(l)The runoff course could be generally divided into "fovea posterior" type and "superior fovea" type, and described with exponential function and log function respectively. With increase in rainfall intensity and slope, the runoff course of "fovea posterior" type transformed into "superior fovea" type. Straw mulch could approve the soil infiltration productively, had obvious influence in small rainfall intensities and slopes. With rainfall intensities and slopes increased, it approved little.(2)The coherence of rainfall intensities and slopes proved motivation of runoff, made the runoff faster. While the straw mulch decreased the raindrops motivation, made it slower and approve the soil infiltration. When the rainfall intensity was less than 54mm/h and the slope was less than 15°, the rate of water conservation was higher than 80%and runoff initiation time is more than 27min. With the increase of the rainfall intensity, the rate of water conservation decreased as parabola. When the rainfall intensity was 125mm/h and the slope was 25°, the rate of water conservation was only 14.25% and the runoff initiation time was delayed in 1.61 min-2.84 min.(3) During lower rainfall intensities effect of slope in runoff generation was more obvious while at higher rainfall intensities slope had little effect on runoff generation. With the rainfall intensity increased, the slope contribution rate decreased while the rainfall intensity contribution increased. The slope contribution rate is lager under mulch over, had more influences on runoff under straw mulch condition.(4)Rainfall was the source and motivation of runoff. The rainfall intensity influenced on runoff course directly. Rainfall intensity was significant negative related with water conservation rate under straw mulch, it was the main factor of runoff.(5) The critical slope of infiltration is 15° on purple soil under indoor artificial rainfall simulation experiments. The water conservation rate had obvious differences in higher slopes under straw mulch. The contribution rate of slope was higher than rainfall intensity and effected runoff amount obviously.To sum up. the form of runoff was relative with rainfall intensity and infiltration mostly on purple soil. When the soil infiltration is less than rainfall intensity, the slope land formed infiltration excess runoff. The runoff formed fast, had strong motivation and a strong ability to erosion soil. When the soil infiltration is higher than rainfall intensity, the rainfall could infiltrate abundantly. The slope land formed runoff yield at nature storage. The runoff formed slowly, had less motivation and ability to erosion soil. It is beneficial to water and soil conservation. The coherence of rainfall intensities and slopes increased the motivation and speed of runoff, decreased the infiltration of soil. The straw mulch decreased the motivation and speed of runoff, increased the infiltration. With the increase of rainfall intensity and slope, the function of infiltration losing increased while the production of water and soil conservation of straw mulch decreased. It should formulate the appropriate measures on straw mulch aimed at various terrain and climate conditions in sloping land on purple soil so that prevent soil and water loss scientific and productively.