| Soil moisture is a limiting factor governing vegetation growth and environmentrestoration especially in semiarid areas like the Loess Plateau region in China, in additionstrong soil and water loss intensified conflict between plant water consumption and soil waterdeficit threatens the growth of artificial forests in this region. This paper was focus on theefficiency utilization of soil and water on the process of eco-economic forest construction inthe hilly Loess Plateau region of Northen Shaanxi province. Study on a new rainwaterharvesting and utilization measure——Rainwater Harvesting and Conservation Ditch (RHCD)that is founded by Special Foundation of National Science&Technology Supporting Plan(Investigation and demonstration of key technologies in cash crop efficient water use inNorthwest ecologically fragile areas). In this study, effects of RHCD on rainwater harvestinand soil structure amelioration, characteristics of water variation, soil water content of RHCDfilled with different material and water-holding characteristics of the filler had been donethrough filed continuous soil water monitoring, determination of soil properties, experimentof rainfall simulation and water immersion test in laboratory. The main conclusions of thisstudy were as follows:(1) The RHCD had better soil water storage capacity than level bench, enhanced by23.14%averagely between July to September in2011. The mean RHCD soil water content ofthree sampling within0-200cm profile were in the order: middle>top>bottom. A comparisonof the different layers showed that the overall soil moisture content was highest in the0-40cm RHCD layer, although there was a decreasing trend from the end of July until the end ofSeptember. The>40-100cm layer was higher than the>100-200cm layer and it wasrelatively stable throughout the observation period. The>100-200cm layer was lowest,although there was an increasing trend. The filler significantly ameliorated the physicalproperties of the bottom10cm soil layer by reducing the bulk density and increasing the soilporosity.(2) The ditches are separately filled with straw (SD), branches (BD) and gravel (GD) andcollected water compared with level bench-terrace value under rain-fed conditions. Storedwater in the BD, GD and SD in October2012were higher than level bench21.79mm,18.28 mm and11.27mm respectively. In October, the depth of soil water restoration in RHCD andlevel bench within the30200cm soil profile is different. The deepest soil water restoration isin the SD and BD, followed by the GD and then the level bench-terrace.(3) Deficit soil water condition is noted in all the treatments during the observationperiod, with the maximum deficit index in August. Soil water deficit in all the treatmentsdeclines across the entire soil profile during the period from September to October. Within100-200cm profile the soil water deficit of RHCD was dicline, however, the level bench wasincreased. The soil water restoration under SD is similar to that under BD in the30200cmsoil profile. It is next followed by GD and then by level bench-terrace.(4) The water-holding amount and rate of straw, substrate and wood crumbs leveled offafter10hours soaking reached maximum, while the water-absorption rate decreased sharplyduring the first0.5hour, then decreased gradually after0.5hour to10hours, and fell to zeroafter10hours nearly. Analyze the water-holding process of these three matetials, we foundthat the water-holding rate increased logarithmically with soaking time, while thewater-absorption rate showed an power function with soaking time. The changes of thegreatest water-interception amount, the effective water-interception amount, the greatestwater-holding amount and the effective water-interception depth were generally similar ofdifferent types of filler, which were in the order: wood crumbs>substrate>straw. The changesof the greatest water-interception rate, the effective water-interception rate and the greatestwater-holding rate were generally similar of different types of filler, which were in the order:straw>wood crumbs> substrate.(5) The water infilitration depth were different among different size RHCD after rainfallsimulation. The size of1×0.3×0.3and1×0.2×0.3RHCD had maxmum infilitration depth inthe middle of ditch, reached70cm after rainfall30min and130cm after72h. However, thesize of1×0.2×0.2RHCD was60cm and110cm respectively. The change of soil watercontent was intensity near the bottom side of slop and high water content zone. In the upperpart of RHCD within the depth of100cm, it will appear a high soil water content zone thatcould reach60%of the field moisture capacity after full filled with water.(6) There were different impoundment amount in different size of RHCD under rainfallsimulation with intensity of0.92mm/min and0.6mm/min. However, the same size RHCDhave small difference in impoundment amount between two types of rainfall intensity. Theimpoundment amount of SD, BD and GD were in the order: SD>GD>BD. |
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