Study On Spatial Variability Of The Field Soil Hydraulic And Saline Properties

Soil hydraulic and saline properties are parameters used to describe soil water and salt movement and distribution. Study on spatial variability of soil hydraulic and saline properties had great significance on guiding the development and application of soil environment, soil tillage, and soil water movement. Based on the measurement of Lou soil samples taken in yangling region along straight lines (scheme one), saline-alkalin sail samples taken in Xinjiang region at different scales of grids (scheme two) and along straight lines (scheme three). Spatial variability of soil hydraulic and saline properties were analyzed by means of principles of classical statistics, geostatistics, spatial autocorrelation theory, wavelet analysis, the BP artificial neural network, multifractal theory, and joint multifractal theory. In order to reveal spatial variability of soil hydraulic and saline properties from different angles. The main conclusions were as following:(1) From the analysis of classical statistics for scheme one, variation coefficients of Brooks-Corey model fitting parameter (α) and saturated hydraulic conductivity (Ks) were larger than 1, belonged to strong variations; variation coefficients of Brooks-Corey model fitting parameter (n) varied from 0.1 to 1, belonged to moderate variation; Brooks-Corey model saturated water content (θs), mass water content(θ) and bulk density(ρ) distributed uniformly, and variation coefficients were smaller than 0.1, belonged to weak variation. For scheme two, most soil hydraulic and saline properties varied to a moderate degree. For scheme three, most of the soil hydraulic and saline properties varied to a moderate degree while pH belonged to weak variation.(2) From the analysis of Geostatistics, most semi-variance theoretical models of soil hydraulic and saline properties of three schemes could be fit with spherical models, and showed moderate variation level.(3) From the analysis of spatial autocorrelation theory for scheme one, spatial autocorrelation degree of soil hydraulic and saline properties were different in four directions, Moran's I coefficients ranged from -0.3 to 0.3, showed that random distribution took up a large proportion. For scheme two, Moran's I coefficients of all the soil hydraulic and saline properties were quite similar in variation, which ranged from -0.8 to 0.6 at all the three scales. For scheme three, Moran's I coefficients of all the soil hydraulic and saline properties were different, but which ranged from -0.5 to 0.4.(4) From the analysis of the wavelet variance map, for scheme one and three, every soil hydraulic and saline properties in space showed at least two scale structures, most of their biggest scale structure appeared near 200 and 64 meter respectively. It suggested that in these positions, the spatial variability information of soil hydraulic and saline properties were more abundant, and spatial distribution structure were more complex.(5) From the analysis of multifractal theory, in scale-free scale from -4 to 4, soil hydraulic and saline properties had multifractal feature. For scheme one, the multifractal features ofθs,θandρwere weak, and the multifractal features of Ks,αand n were obvious. According to the calculations of generalized dimensions of soil hydraulic and saline properties, spatial variability ofθs,θandρwere weak, the spatial variability of Ks was stronger thanαand n, suggested that spatial structure of Ks was more complex. For scheme three, soil salt content, WDPT, pH, Na⁺, Mg²⁺, and Ca²⁺ had multifractal structure, but multifractal features of pH was not obvious, suggested that spatial variability of pH was weak.(6) From joint multifractal analyse for spatial correlation of soil hydraulic and saline properties, for scheme one, the result showed that in the first program spatial correlation between Ks andα, n, and betweenρand n were weak, spatial correlation between Ks andθs,ρ,θ, and betweenρandαwere strong. For scheme three, spatial correlation between salt content and pH, Na⁺, Mg²⁺, Ca²⁺, between Na⁺ and Mg²⁺, Ca²⁺, between Mg²⁺ and Ca²⁺ , WDPT were strong.