The Regulation Effects Of Combining Level Ditch And Infiltration Hole On The Slope Water In The Loess Plateau

The degraded ecosystem caused by human activities and climate change has affected the harmonious relationship between human and nature,vegetation restoration is an important approach to mitigate climate warming and restore the degraded ecosystem.The Chinese Loess Plateau has the fragile ecological environment,the vegetation restoration in the Loess Plateau has been obviously improved,but the excessive water depletion,the aggravated soil desiccation and the poor vegetation growth have seriously threatened the stability of vegetation ecosystem and the sustainability of ecosystem services.The severe soil erosion in the Loess Plateau results in the loss of soil water and nutrient resources of slope.Under the context of global climate change aggravation and the continuous vegetation restoration,the shortage of soil water and nutrient resources is the main limiting factors to limit the stability and sustainability of slope vegetation ecosystem in the Loess Plateau,how to further improve the utilization of rainfall runoff on slope has become an important scientific and technical problem to be solved in alleviating the shortage of soil water and nutrient of the slope in the process of vegetation restoration.The combination of level ditch and infiltration hole is a technical measure for enhancing the utilization of rainfall runoff.The soil column experiment was constructed to accurately quantify the soil water evaporation effects of the infiltration hole.Two field experiments were conducted on the typical slope of the Loess Plateau to determine the effects of the combined measure on slope rainfall runoff and soil water re-distribution and study the improved effects in soil water and nutrient environment of the slope planted with Caragana korshinskii under the combined measure,respectively.The main results of this study are showed as follows:（1）Under the high initial soil water content condition,in day 0 to day 26,the average increase of the daily evaporation of the infiltration holes with the different depths（20 cm、40cm、60 cm、80 cm）was 14.14%,in day 31 to day 96,their average decrease was 10.63%,the evaporation effects did not intensify with the depth of infiltration hole.In the whole evaporation period,the average daily evaporation of covering the top surface of infiltration hole and the inner surface（the sidewall and the bottom of the hole）of infiltration hole was decreased by 74.25%and 4.25%than that of the infiltration hole without any cover,respectively.The soil water was mainly evaporated through the top surface of the infiltration hole rather than the infiltration hole itself.After the rainfall of 100 mm h^-1,the infiltration hole,gravel mulching,branch mulching,the combination of infiltration hole and gravel mulching,and the combination of infiltration hole and branch mulching could reduce soil evaporation,in day 97,their cumulative evaporation was significantly reduced by 61.40%,33.47%,41.50%,54.15%,and 63.50%,respectively.Compared with gravel mulching and branch mulching,the average daily evaporation in day 14 to day 97 under the infiltration hole was significantly decreased by 65.36%and 59.50%,respectively.During the later evaporation stage,the effect in reducing soil evaporation was better under the infiltration hole than the mulching.During the whole evaporation period,the combination of infiltration hole and branch mulching was the most effective measure for reducing soil evaporation after rainfall event.（2）Under the high slope runoff yield,the combination of level ditch and infiltration hole had more effective effects in reducing runoff and sediments compared with the level ditch.In rain season,the combined measure significantly increased the soil water content of different layers of 70–200 cm in upper slope and 70–280 cm in lower slope.After two rain seasons,the soil water storage of soil profile of 0–300 cm in the level ditch of upper and lower slope under the combined measure was significantly increased by 18.57%and 19.30%,respectively,the increase was in the soil profile of 50–200 cm in upper slope and in the soil profile of 50–300cm in lower slope.The contribution rate of infiltration hole in the effects of the combined measure on the soil water storage of 0–300 cm in the level ditch of upper and lower slope was104.15%and 98.18%,respectively.The soil water environments of all the different locations of 0,15 cm,30 cm in horizontal direction from infiltration hole under the combined measure were better compared with the soil water environments in the level ditch without infiltration hole,the improvement effects were decreased with the increase in the distance from infiltration hole.Compared with the level ditch without infiltration hole,the average increase of the soil water storage of soil profile of 0–300 cm in upper and lower slope at the locations of 0,15 cm,and 30 cm in horizontal direction from infiltration hole was 19.18%,9.45%,and 5.37%,respectively.（3）In dry season,all the branch mulching,the infiltration hole and the combination of infiltration hole and branch mulching had no significant effects on the soil water storage of soil profile of 0–380 cm in level ditch.In wet season,the infiltration hole and the combined measure significantly increased the soil water storage of soil profile of 50–150 cm in level ditch and their impact depth were up to 300 cm with the increase in the runoff yield intercepted by level ditch,however,the branch mulching just increased the soil water storage of soil profile of 0–50 cm in level ditch.After two rain seasons,the replenishment depth of rainfall runoff under the infiltration hole and the combined measure was increased by 40 cm and 30 cm,respectively.The soil water storage of soil profile of 0–380 cm in level ditch was significantly increased by 116.20%under the infiltration hole.The infiltration hole and the combined measure significantly recovered the soil water environment of soil profile of 50–150 cm in level ditch,the main contribution of the improved effects of the combined measure on deep soil water was from infiltration hole,combining branch mulching to the level ditch with infiltration hole reduced the soil water replenishment from rainfall runoff.（4）After two rain seasons,the infiltration hole and the combination of infiltration hole and branch mulching could significantly improve the average soil organic matter and soil total nitrogen content of soil profile of 0–120 cm in the level ditch of the slope planted with Caragana korshinskii,however,no significant improved effect was found under the branch mulching.The mulching mainly improved the soil nutrient environment of the layer of 0–10cm rather than the deeper layers,the infiltration hole and the combined measure significantly increased the soil nutrient content of the layers of 60–100 cm.The carbon\nitrogen storage of soil profile of 0–120 cm was decreased in the level ditch without any measure after two rain reasons,however,the one was significantly increased in the level ditch with the infiltration hole or the combined measure,the more obvious effects were found in the soil profile of 80–120 cm.（5）The infiltration hole and the combination of infiltration hole and branch mulching had obviously improved soil water and nutrient environment in the level ditch of the slope planted with Caragana korshinskii,however,these were insufficient to significantly change the basal diameter,the canopy diameter and the plant height of Caragana korshinskii in statistics.A longer experimental period needs to be carried out for accurately evaluating the effects of infiltration hole on the growth of Caragana korshinskii in level ditch.Overall,the combination of level ditch and infiltration hole can regulate rainfall runoff,this can effectively inhibit soil evaporation after rainfall event,significantly increase the water supplement of rainfall runoff on deep soil layers,and obviously improve soil water and nutrient environment of deep layers.The main contribution of the improved effects of the combined measure on soil environment of deep layer was from infiltration hole.The study provides the scientific basis and an effective technical measure to alleviate the shortage of soil water and nutrient of slope and the soil desiccation of deep soil layers in the Loess Plateau and promote the health and stability of slope vegetation ecosystem in the Loess Plateau.