Study On Runoff Regulation Of The Hedgerow In Semi-arid Area

Hedgerow technology is widely used in projects of soil and water conservation andecological construction in China. However, it is still unclear that how the hedgerow systemkeeps its own stability through soil hydraulic redistribution. We take the Caragana intermediahedgerow（26-year-old）and Prunus armeniaca hedgerow（8-year-old）, located in Loess HillsRegion, as the research object. This paper analyzes the spatial distribution characteristics anddynamic features of soil moisture in different position, and discusses the river runoff regulationeffects of hedgerow system as well as the moisture redistribution process on the basis ofstudying soil mechanical composition, water-stable aggregates, water physical property in soil,nutrient content and soil permeability of different position (inter-band, front of band,inner-band and behind of band), as well as observing soil moisture content during2years.Results are as follows:(1) It is obvious that the hedgerow has a pronounced effect on the ameliorating of soil,and there are some differences of soil particle composition in different parts of the system. Inhedgerow system, soil clay content and aggregate content are all higher than the cultivated land.The soil clay content of inner-band is up to20.88%, which is the highest of the system. It isdemonstrated a trend that the particle size>0.25mm water-stable aggregates is enriched ininner-band, especially in topsoil. However, in Prunus armeniaca hedgerow, inter-band soilaggregate structure is superior to the inner-band, besides, inner-band soil sand content is higherthan other parts of the system. Maybe it could be attributed to the long-term cultivation ofalfalfa which improves the inter-band surface soil structure.(2) In Caragana intermedia hedgerow, inner-band soil is more porous, and has betterpermeablity performance and water retention capacity. In front of the band, surface soil densityis1.16mg·m-3, the highest in the system, but its water retention capacity is poorer. In Prunusarmeniaca hedgerow, the inner-band soil structure is not obviously optimum, but soil physical structure in hedgerow is better than the check, which demonstrates that the hedgerow has veryobvious role for improving soil. Statistics indicate that soil moisture content of the inner-bandpart of both Caragana intermedia and Prunus armeniaca is the highest in the same matricpotential. Meanwhile, during the wetting and drying process of soil, water characteristic curveof the two hedgerows’ soil shows hysteresis phenomenon. In the same matric potential, watercontent of drying process is higher than wetting process which indicates that the waterretention capacity of Caragana intermedia is superior to Prunus armeniaca obviously.(3) Same as the trend of soil water physical property, in Caragana intermedia hedgerow,soil organic matter and total nitrogen are showing a trend of converging to the inner-band, butcontent of the organic matter in front of the band is the lowest in the system which may beascribed to the damage of topsoil during the process of planting hedgerow. However, soilalkali-hydrolyzable nitrogen is not significantly enriched to the inner-band, which may be dueto the fact that the soil alkali-hydrolyzable nitrogen is easy to leaching loss in condition ofpreferable soil pore structure in inner-band. In Prunus armeniaca hedgerow, soil fertility ofinter-band is higher than the inner-band, which is in connection with long-term cultivation ofherbage in inter-band.(4) Wetting front advancing speed of inner-band is faster. Infiltration rate is higher thaninter-band, and the capacity of water penetration and replenishing is stronger.(5) With the increase of soil depth, soil moisture content of Caragana intermediahedgerow is decreased gradually, following by0-20cm(20.35%±11.56%)＞40-60cm(10.37±5.90%)＞60-80cm(8.02±4.50%)＞80-100cm(7.33±4.14%)＞100-120cm(6.94±3.94%), and converged on the front of the band and inner-band. According tothe orderly cluster analysis on soil moisture, the profile of soil moisture in the hedgerowsystem can be divided into three layers: weak moisture utilizing layer, moisture utilizing layer,and moisture regulating layer. Moisture utilizing layer of inner-band soil (20-120cm) is greaterthan soil in the front of the band, behind of band (20-60cm) and inter-band (40-60cm). It is inline with the utilization depth of soil moisture by plants. The moisture regulating layer of inner-band soil is below120cm, which is deeper than inter-band (below80cm), front of theband and behind of band (below60cm). It embodies the effect of intercepting runoff, enrichingsoil moisture to the inner-band, water infiltrating and reserving which the hedgerow has onsoil.