Water Transformation And Simulation Of Soil-artificial Vegetation-atmosphere-transfer In The Farming-pastoral Zone Of The Loess Plateau

In the farming-pastoral zone of the Loess Plateau, with arid and semi-arid climate and scarce precipitation, the majority of vegetation distribution is patchy with lower biomass and relatively small canopy. Research on the water movement and transformation of soil- vegetation-atmosphere-transfer can reveal the water consumption characteristics of the representative sparse vegetation in the region, and it will help to establish sustainable development ecosystem. In this study, in order to understand the water consumption and movement in different SVATs, the spatial distribution of fine roots of typical trees, shrubs and grasses species were investigated, the components of SVAT system water balance were monitored. In addition, SHAW model was used to simulate energy and water transmission among the components of SVAT system under different land use patterns, long-term water consumption process of typical vegetation were also simulated, and the suitable vegetation coverage were determined by the relationship between vegetation and soil water in this area. The main conclusions of this study are as follows:(1)More fine roots of representative arbors and shrubs in the Liudaogou Basin occurred in the upper 100 cm soil layer and fewer were below 100 cm. The majority of fine roots of Robinia pseudoacacia concentrated in 0-340 cm; for Caragana korshinkii which grown in loess soil and Salix psammophila were both 0-300 cm; the fine roots of C. korshinkii in sandy soil and Artemisia ordosica mainly concentrated in 0-200 cm. The proportion of fine roots in 0-100 cm of total fine roots was C. korshinkii in sandy soil>A. ordosica>C. korshinkii in loess soil> S. psammophila>R. pseudoacacia.(2)The soil water in profile was greatly affected by different land use patterns. The soil water condition was better in P. tabulaeformis and A. ordosica land, but R. pseudoacacia, P. simonii, S. psammophila, C. korshinkii and S. psammophila-C. korshinkii- A. ordosica were suffered different levels of water stress, especially the soil moisture content was very low in 0-200 cm soil layer. 20 years old C. korshinkii grown in different soils all strongly consumed the soil water in 0-200 cm, but they had different effect on the soil water below 200 cm. The soil water condition was relatively good in red clay soil and hard loess soil, followed by aeolian soil and sandy soil, the lower soil water occurred in sandy loess soil. 3-5 years old M. sativa used more water in 0-280 cm soil layer, the soil water storage was only half of the farmland at the 3th year.(3)The water balance of different land use patterns indicated that the soil water kept balance for the P. tabulaeformis and C. korshinkii which grown in silt loam soil over the whole study period, the average evapotranspiration/precipitation (ET/P) was 97.6% and 98.3%, respectively; but the soil water storage was deficit for 3-5 years old M. sativa land, and the average ET/P was 107.5%. The soil water also remained balance for the S. psammophila, A. ordosica and C. korshinkii which grown in sandy soil during the same period, the average ET/P changed from 95.7% to 98.8%; the average evapotranspiration for R. pseudoacacia, P. simonii and S. psammophila-C. korshinkii-A. ordosica lands slightly exceeded precipitation, the average ET/P were 103%, 101.6%and 101.1%, respectively.(4)SHAW model could be used to simulate the dynamics of solar radiation and soil water. The simulated net solar radiation was in good agreement with the measured values, and the relative mean absolute error (RMAE) was around 21%. The soil water model efficiency (ME) for P. tabulaeformis, C. korshinkii and M. sativa land over two growing seasons was from 0.54 to 0.82, RMAE changed between 9.2% and 12.9%. Energy balance showed that, the major consumption of energy was the latent heat of evapotranspiration for M. sativa, S. breviflora and Millet at the shade slope, but the energy consumption was mainly sensible heat for P. tabulaeformis and C. korshinkii at the sunny slope.(5)Considered the relationship between the suitable amount of soil erosion and moderate soil water consumption by plants and the vegetation coverage, the suitable coverage for M. sativa and C. korshinkii in hillslope was 33%-40% and 25%-32%, respectively.