Soil Water Balanc Of Typical Artificial And Natural Grasslands In The Semi-arid Loess Plateau

Soil moisture is the most important restrict factor for vegetation restoration in arid and semi-arid regions.The natural rainfall is the only source for soil moisture supplement.Thus,unreasonable way of vegetation restoration could aggravate soil moisture deficit and against the vegetation sustainable development.Hence,establishment of artificial grasslands and natural grasslands are the two choices for vegetation restoration,because of the soil moisture condition in the Loess Plateau.In order to research the soil water balance characteristics of typical artificial and natural grasslands in Loess Plateau,we studied the artificial cultivation Caragana korshinskii grassland,Medicago sativa grassland and Agropyron cristatum grassland,as well as the Stipa capillata natural grassland.Soil moisture variation,evapotranspiration variation,water use efficiency,soil moisture deficit and replenishment as well as soil water balance characteristics were analyzed.The results showed that:(1)Water consumption of artificial grasslands was more than the natural grassland.Legume grasslands consume more water than gramineous grasslands.In artificial grasslands,soil moisture seasonal changes rapidly in the 0-100 cm depth,and 0-30 cm in natural grassland.Soil moisture vertical variation was increase-decrease in legume grasslands,and increase-decrease-increase in gramineous grasslands.Compared to first growing season,soil moisture was increased in natural grasslands.However,there were 3%-6% decrease in legume and 1% decrease in gramineous of artificial grasslands.Artificial grasslands would continuously consume soil moisture.(2)Higher precipitation use efficiency and water use efficiency of artificial grasslands could promote the increase of above-ground biomass.When above-ground biomass increased rapidly,evapotranspiration also reached peak value.Evapotranspiration of artificial grasslands was lower than natural grassland in June.In the mid and end growing season,it was higher in artificial grasslands than natural grassland.In the first growing season,evapotranspiration was exceed precipitation supplement,soil moisture was keep balance in natural grassland and negative balance in artificial grasslands.(3)The soil water storage deficit would aggravate at the end of the growing season with the increasing planting years.And the soil moisture deficit of legume grasslands was more serious than gramineous grasslands.The soil moisture deficit increased approximately 4% in legume grasslands and 0.5% in gramineous grasslands compared to first growing season.To the contrary,the natural grasslands decreased about 2%.During the growing season,the soil water storage deficit variation was increased and decreased,and the highest value was in August.At the end of growing season,soil water storage deficit was not completely supplement,the deficit compensation degree was higher in gramineous grasslands than legume grasslands.(4)The infiltration rate was higher in artificial grasslands than natural grasslands.The infiltration rate of legume grasslands was 30% higher than gramineous grasslands.The main factors for determining the infiltration rate were below-ground biomass,total porosity,capillary porosity,soil organic matters and water-stable aggregate.The capillary porosity had a negative effect on infiltration rate in the top soil depth.In the 10-30 cm depth,below-ground biomass could significantly increase the infiltration rate.Legume grasslands could increase the supplement of rainfall to soil.However,it was restricted,due to the less precipitation in arid and semi-arid regions.The soil moisture consumption was higher in artificial grasslands than natural grasslands.Due to the higher infiltration rate of artificial grasslands,precipitation use efficiency were higher in artificial grasslands than in natural grasslands,as well as aggravated the soil water storage deficit.In the little rain and arid environment condition of Loess Plateau,artificial grasslands would constantly aggravate soil water deficit and natural grasslands would maintain a better soil water condition with increasing years of planting.Thus,natural grasslands could sustainable development in the semi-arid Loess Plateau.