Profile texture configuration of the soil in alluvial plains is a crucial factor determining soil water and nutrient conserving and supplying capacity and water and salt movement in the soil. Among the six major soil-forming factors in this regional soil, topography stands out to be the most prominent one. Analysis of the influence of topography on soil profile texture configuration is of important theoretical and practical significance to guiding agricultural production. Using the fuzzy c-means algorithm model nine soil profiles different in texture configuration was defined. Based on the data of thicknesses of the characteristic texture layers of nine soil profiles including sandy, loamy and clayey, surface layers, (0-(30±10)cm), sandy, loamy and clayey center layers((30±10)cm-(60±10)cm)and sandy, loamy and clayey bottom layers((60±10)cm-(90±10)cm), nine types of soil profile texture configuration were identified, i.e. loam-clay-loam, loam-loam-clay, loam-clay-clay, clay-clay-clay, sand-sand-clay, sand-sand-sand, sand-loam-loam, loam-loam-sand and loam-loam-loam, among which loam-loam-loam and sand-sand-sand were the dominant types. As a result of frequent flooding by the Yellow River in history, complex process of sediment deposition, and in addition farming practices and soil amelioration measures, like irrigation, deep plowing and field leveling, soil profile texture configuration varied sharply in distribution at a small spatial scale.
Comparison analysis of the influence of landform on soil texture profile configuration in the whole study area and the typical area relatively concentrated with various types of soil profile texture configuration, shows that a positive correlation always exists between membership value of the soil profile texture configuration of the sand-sand-sand type and elevation, suggesting that the law prevails that soils in lands relatively high in elevation tend to be sandy, while the influence of landform on soil profile texture configuration of other types, and soil texture of the 0-60cm soil layer, surface soil layer, subsoil layer and bottom soil layer, does not follow any specific law. The reason is probably that as the influence factor of soil profile texture configuration is relatively simple in the typical area than in the whole study area; elevation can be viewed as the main factor controlling spatial distribution of various types of soil profile texture configuration. Based on the definition of 0-60cm texture control layer, soil profile texture configurations with the same texture function layer or texture control layer were collated. It was found that the soils with a texture control layer of the sand-sand-loam type were generally distributed in areas on average over 70m in elevation, while the soils with a texture control layer of the loam type or the loam-clay type were in areas that did not vary much in average elevation, i.e. below 70 m. The two were often overlapped in distribution at a micro-region scope.
At the study area scope, the spatial and temporal heterogeneity of the sedimentary environment, the wind transporting process and the soil farming and amelioration practices, such as local irrigation sedimentation, deep tillage, was great, which to a large extent reduced and masked the influence of elevation on spatial distribution of soil profile texture configuration. The higher the elevation of the parts of landform, the fewer the type of soil profile texture configuration developed; and the lower the elevation, the more the type developed. Moreover, the parts lower in elevation are often complex in soil profile texture configuration, and higher in elevation, simple in soil profile texture configuration. Areas complex in soil profile texture configurations may have been subjected to exposure of human interference, and as a result that the influence of landform on soil profile texture configuration does not have any specific law to follow.