Spatial Distribution Of Soil Quality On Cropland Under Different Landscape Positions In The Loess Plateau Of China

For the purpose of knowing the distributing law of on-farm soil factors under different landscape positions in the semi-arid area of Loess Plateau, and studying the soil factors mianly correlated with crop biomass, the research was conducted on the Loess Plateau Experimental Station of Lanzhou University, in zhonglianchuan area, Yuzhong county, Gansu Province. Treatments were adopted as follows: we selected four different aspects respectively: East (E, 85°), South (S, 174°), West (W, 263°) and North (N, 0°) . Four different vertical positions (namely slope positions) also selected from every aspects respectively according to altitude difference, there were: adjacented bottom land (AB), lower slope (LS), middle slope (MS) and upper slope (US). The interval of altitude between adjacent slope positions was about 25 m. We regarded every slope position as a sampling belt, and took fhe sample of soil and crop biomass on the farm land which planted three major crops (pea, spring wheat and potato). Such results were obtained as follows:The distributing law of physical factors about soil quality: The soil temperature of BL was significantly higher (p<0.05) than other slope positions in Winter, but there was no difference between them in Spring. During the depth of 10cm, the soil temperature of LS changed when the direction of wind altered, and it was lower on the wind-facing slope. Bulk density had negative linear correlation with altitude(or elevation), and had positive quadratic correlation with slope. Also, positive quadratic correlation was existed between bulk density and aspect. More the north aspect deflects, more bulk density is. Totally, The rank of soil moisture (0-100cm depth) from highest to lowest is : BL>MS>LS>US. the soil moisture of slope positions changed when the direction of wind altered, and it was lower on the wind-facing slope. During the depth of 40-100cm, soil moisture had negative quadratic correlation with slope. megative linear correlation was existed between soil moisture and altitude.The distributing law of chemical factors about soil quality on different vertical positions: (1)The factors which existed in US and MS were significantly higher (p<0.05) than LS and AB: total organic carbon(TOC), light fraction of organic carbon (LFOC), total soil nitrogen (TSN) and C/N. (2)The factors which existed in LS and AB were significantly higher (p<0.05) than US and MS: NO₃^--N, total soil phosphorus (TSP) and available phosphorus (AP). (3)The factors which didn't have any significant difference among vertical positions: C/N and pH. The distributing law of chemical factors about soil quality among different apects: (1) The factors which existed in slope positions facing east were significantly higher (p<0.05) than it facing other directions: TOC, TSN, TSP, C/N and C/P. (2) The factors which existed in slope positions facing north were significantly higher (p<0.05) than it facing other directions: LFOC. (3) The factors which didn't have any significant difference among aspects: NO₃^--N, AP and pH.The distributing law of biological factors about soil quality: There was positive linear correlation between soil biomass carbon (MBC) and soil mineral nitrogen.During the depth of 0-20cm, the above-ground biomass of pea had significant correlation (p<0.05) with soil moisture, pH and MBC respectively, and the value of Sig. were 0.029, 0.045 and 0.046 respectively. Although the above-ground biomass of spring wheat didn't have significant correlation with soil factors, the degree of correlation between it and TOC, TSN, C/N were the mot during the depth of 0-20cm, and the value of Sig. were 0.169, 0.185 and 0.244 respectively. Also, although the above-ground biomass of potato didn't have significant correlation with soil factors, the degree of correlation between it and C/P,AP, bulk density were the mot during the depth of 0-20cm, and the value of Sig. were 0.132, 0.263 and 0.279 respectively.According to the experimental results mentioned above, we advise that the investigated area should adjust measures to local conditions: For exemple, developing efficient and special agriculture on AB; Enhancing the soil moisture and heat management to accelerate mineralization of organic matter on MS and US; Adjusting the gradient of slope and returning farmland to grassland and shrub-land so as to enhance the capability of water maintenance in soil. According to the differences of soil condition, the three major crops as pea, spring wheat and potato had better be arranged rationally under suitable landscape positions.