Evaluation And Simulation Of Soil Reservoir Dynamic Property In Loess Plateau In Northern Shaanxi Province

Soil moisture condition is the key which restricts the ecological restoration of the area ,and is also the determinate factor which maintains the sustainable development of agriculture in Loess Plateau. Gaopo village in Baota District in Yan'an, Nihegou Watershed in Chun'hua and Quanjiagou Watershed in Mi'zhi are taken as the area of coverage in this paper. Through position monitoring soil moisture in different land utilization, the character of soil reservoir is analyzed systematically in Loess plateau in northern Shaanxi Province by using the methods of fixed quantity and fixed quality and combination of model simulation and observation comparison. The conclusions are obtained as follows:Submerged soils in Loess plateau, which bring a huge storage capacity into the soil reservoir, are usually in anhydrous condition due to the effect of precipitation infiltration and supply. The change of measured soil moisture content of each layer is fluctuant as it's affected by the soil moisture content change and inaccuracy of measurement. When the depth that corresponds to the minimum of the soil moisture content fluctuant change is taken as the adjusting depth, the adjusting depth of soil reservoir in sunny slope orchard and sunny slope locust in Northern Shaanxi Province is the least, the shady grassland and farmland is the largest, and the soil adjusting depth of the other slope aspects and land utilizations is intervenient. The modulability of soil reservoir in shady slope farmland and wild grassland is the largest, that is 1194.96mm, the sunny slope orchard and locust is the least, that is 597.48mm, and the modulability of the other slope aspect and land utilization is between them.Domatic soil reservoir have different character as it is affected by multifactor such as zonation, land utilization, slope location, slope aspect, the length of land use and land-use density ect. In zonation aspect, soil water storage grows downwards obviously from the south to the north. In land-use aspect, soil water storage in farmland and wild grassland is obviously higher than that in orchard and locust. In slope aspect, sunny and semisunny slope are obviously lower than shady and semishady slope. In the same slope aspect, water content in the upper is lower than the middle and the abdominal. Soil gets dry obviously under the 200cm soil layer in the locust with the age of 16 along with the length of land use being increasing and water storage was being decreasing. At the mean time, the vegetation density also affects the soil water storage directly. Water storage decreases with the dengsity increasing.Soil reservoir storage is affected by the factor such as precipitation, evaporation and so on , which presents fluctuant change annually and interannually. With the time series theory application, soil reservoir capacity tendency mean value in orchard, locust, grassland and farmland are 250.16mm, 95.02mm, 84.75mm and 55.86mm respectively. The discipline of soil reservoir seasonal change is that: soil moisture is in the phase of slow cumulating in autumn and winter, in the phase of strong consumption in late spring and early summer, and in the phase of fluctuant change in summer. Soil reservoir is adjusting precipitation and evapotranspiration, showing that water storage, which provides plants for their growth consumption, decreases in the first part of year, and that it is supplied by infiltration in the second part of year, storage precipitation. Soil reservoir gets supply from the infiltration in 2003 and 2005, which makes the water storage increasing. Soil moisture is consumed in 2002, 2004 and 2006 when the measured soil reservoir maximum regulated quantities in orchard, locust, grassland and farmland are 245.38mm, 328.18mm, 284.78mm and 261.62mm respectively.Soil moisture is divided into unavailable water, difficult available water, middle available water, readily available water, and saturation water, according to the difficulty level of plants drinking in moisture from the soil. The validity of soil moisture in domatic orchard, locust, farmland and wild grassland recedes into the north, that is Chun'hua > Yan'an >Mi'zhi. In different slope aspects, It's showed that the validity of soil moisture registers in sunny slope is the worst, shady slope the best, and semishady, semisunny slope and hilly top is between them.Annul soil moisture keeps in step with the season, showing that soil moisture is high integrally in Jan. and validity decreases gradually with the evapotranspiration of soil moisture, and that soil moisture in the 0-40 surface layer is unavailable water in Jun. and validity of soil moisture is recovered in a certain extent for the effect of precipitation supplement. Econiche of soil moisture of different land use type is obtained by taking portion of root in each soil layer as weight, which shows that in different land use types, soil moisture niche fitness in Chun'hua is the highest, Mi'zhi the lowest and Yan'an between them, and that in different slope aspects, soil moisture niche fitness in sunny slope is the lowest, shady slope the highest and semishady, semisunny slope and hilly top between them, and that in deferent land utilization, soil moisture niche fitness in farmland is the highest, locust higher, grassland and orchard lower and that soil moisture niche fitness of all land utilizations reaches the lowest in July, after which soil moisture econiche gets a raise due to the infiltration supplement, and that the longer age of domatic locust is, the lower soil moisture niche fitness is, which restricts the growth of wood in a certain extent and that the larger the density of forest is, the lower soil moisture niche fitness is.With the application of linear disturbing theory, soil reservoir water yield linear disturbing model is built, taking the random value of precipitation and referenced crop evapotranspiration as output , simulating the random value of soil water storage, adding the tendency and periods of soil reservoir water storage and forming the response of soil reservoir water storage to precipitation and evaporation, and make sure that each memory length of soil reservoir linear disturbing model is 12 periods of time, namely six months. Empirical linear disturbing model can describe, soil reservoir water storage very well. Soil reservoir water storage in 2006 is predicted by using the model which can predict the change of soil reservoir water storage very well, for the deviation between simulated value and measured value in other periods is very small through analyzing the forecast precision of the model, except for in individual period when the error is largish.