Study On Runoff Sediment And Benefits Of Supplement Irrigation In Watershed Of Ninxia's Mountainous Areas

In order to find out the rule of runoff and sediment and the benefits of soil complemental irrigation in south Ningxia's mountainous areas, so as to serve its ecological environment restoration, standard runoff fields were set up at Daping Experimental Station for Soil and Water Conservation in Xiji county, Ninxia. Runoff and sediment were observed through corresponding facilities due to different slope and land use so as to analyze the effect of precipitation, slope, land use on runoff and sediment. The results shows:1. Under experimental condition, the runoff yield is very low(only 7.3mm) and account for 2% of yearly precipitation.2. The runoff volume is relevant to precipitation intensity of max 30min, slope, land use and soil moisture.The runoff volume on slope land and grassland increases with the rise of slope gradient and reaches its maxim at 20°,then decreases with slope rise, while increases evenly on forest land between 10°～25°.The way of land-use is an important factor to affect the slope runoff. From the precipitation data between 1993～1996, we know that the runoff volume on slope land is the least, the forest land middle and the grassland the most, which is 6.4mm, 6.9mm and 7.9 mm per year respectively.The runoff volume will differ greatly under different precipitation because of different soil moisture. Higher pre soil moisture avails the runoff and vice versa.3.The sediment yield is greatly related to the precipitation properties, slope gradient, land-use and soil moisture.The experiment shows that under similar precipitation, the sediment yield on runoff plot with natural slope is more than that of standard plot.The slope erosion yield show direct ratio to slope gradient. Different land-use leads to different sediment yield even though under the same slope and precipitation, among them it is the least on slope wildland.The times of sediment generation shows direct ratio to yearly precipitation, slope and the times of precipitation on standard runoff plot.4.Use of dry land terrace can increase yield stably and remarkably by more than once. The crop yield on slope land is the least among slope, dryland and irrigated terrace, and the highest on irrigated terrace. The average yearly yield on slope, dryland terrace, 1:1 and 2:1 irrigated terrace is 1172kg, 2415kg,3008kg and 3216 kg respectively and the catchment area has little effect on crop yield.The crop yield decreases with slope increase by 3% every 1°, while for the irrigated terrace it increases by 3%.This experiment also shows that it is fundamental to develop sustainable agriculture by use of terraced land. The crop yield can increase greatly when slope land is transformed to terraced land. What's more, the application of advanced agricultural technology can improve the soil output more.5. Complemental irrigation can increase crop yield by 25% and different irrigation modes have different water-saving and economic benefits.The irrigation water volume differs greatly under different irrigation modes. For point irrigation, mulched irrigation and gravity irrigation, it needs 375m3 , 105m3 and 950m3 water respectively. Water is insufficient in south Ninxia's mountainous areas and it is the key factor to restrict agricultural development, therefore, to develop water-saving irrigation such as point irrigation and mulched irrigation is quite imperative.