| Topography is an important factor affecting the nature of the soil. Quantitative study of the correlation between terrain factors and soil properties has an important significance for the rational utilization of soil resources in the hilly areas, soil conservation and ecological environment construction. Recent studies on the differentiation characteristics has mostly concentrated on the nature of the soil under a single topographic factor, however, little in different combination of topography and the rehabilitation and reconstruction of agriculture in the disaster area of the earthquake. By the analysis of geo-statistic, the characteristics of spatial variability under farmland scale, the differentiation of the soil property under different terrain factors and different combination of terrain factors through establishing Digital Elevation Model was studied based on Arc GIS9.0. The study area was in a village of Mianyang in Sichuan province, which was heavy hit in the "5.12" earthquake. The results indicated that:1 In the study, most soil was neutral to weak alkaline. The content of the total nitrogen, available nitrogen, total potassium, available potassium, total phosphorus, available phosphorus and organic matter was 0.37 g kg-1,87.34 mg kg-1,18.69 g kg-1,69.38mg kg-1, 0.91 g kg-1,18.00 mg kg-1 and 19.60 g kg-1. The level of the content of the total nitrogen is very lacking, which of available nitrogen, available potassium and organic matter were lacking, while available phosphorus was in the medium level. The coefficient of variation of the soil nutrient factors was between 0.1 and 1 indicating that the soil nutrient factors were intermediate variability.2 The semi-variance function model indicated that total nitrogen fitted linear model good. The available nitrogen, total potassium and total phosphorus fitted index model. While the available phosphorus, organic matter and pH was good fitting Gaussian model. The nugget of all the soil nutrients was less than 25%. The nugget of total nitrogen, available nitrogen, total potassium, available potassium, total phosphorus, available phosphorus, organic matter and pH was 10.62%,10.13%,3.69%,0.09%,0.28%,0.22%, 2.94% and 0.16%, respectively. These results indicated that the description of soil properties in the region has a strong spatial variability; the distribution was mainly affected by the structural factors.3 The content of nitrogen in the study area was highest in the northwest. The highest content of total nitrogen was 0.88g kg-1 and that of available nitrogen was 173.23mg kg-1. The content of total nitrogen and available nitrogen was gradually decreased to the central showing annular plaque. The content of potassium was highest in west south. The highest content of total potassium was 29.15 g kg-1 and that of available potassium was 247.56 mg kg-1. The lowest content of total potassium was 3.80 g kg-1 in north. The content of available potassium was lowest at the top of hillock in the central and gradually increased to outside. The lowest content of total phosphorus plague was in south and north and the value was 0.13g kg-1. The higher content of total phosphorus was in west. The spatial distribution of available phosphor showed a high content zone along northwest-southeast. The lowest content of organic matter was 8.30g kg-1 in the central of hillock. The content of organic matter gradually increased along with the decrease of the slope position showing as a annular, and that in west was higher than in east. The spatial distribution of pH showed that acidic soil was in northwest and the calcareous soil was in west, central and north.4 The results of correlation between the soil properties and terrain factors indicated that: the soil properties were negatively correlated with the elevation except pH. The correlation coefficient between elevation and total nitrogen, available potassium, available phosphorus, organic matter was -0.121,-0.121,-0.118 and -0.135. In the 0-180°azimuth, total nitrogen, available potassium, total phosphorus, organic matter was negatively correlated with aspect. Among them, total nitrogen, available nitrogen, organic matter and aspect was significantly negative correlation, with the coefficient of-0.257,-0.321 and-0.317; In the 180-360°azimuth, total nitrogen, available nitrogen, available potassium, organic matter is positively correlated with the aspect, the contents was gradually increased from south to north. Total potassium, total phosphorus, available phosphorus and pH were negatively correlated with aspect in this azimuth. All the soil elements in the study were negatively correlated with the slope shape, indicating that serious soil and water loss and pure capability of preserving fertility were on the convexity slope. The factors of ground curvature were positively correlated with soil elements.5 Under different slope position, the total nitrogen, available nitrogen, total potassium, available potassium, total phosphorus, available phosphorus and organic matter decreased with the increase of slope position and significantly correlated with the slope position. The content of total nitrogen, available nitrogen, total phosphorus, available phosphorus and organic matter was highest in the gentle slope, which were 0.39 g kg-1,90.41 mg kg-1, 0.96g kg-1,18.75 mg kg-1 and 20.20 g kg-1. As the slope steepened, their content gradually decreased. The content of total nitrogen, available nitrogen, available potassium, total phosphorus and organic matter was highest on the linear slope, and lowest on the convex slope. The content of total potassium was highest on the convex slope. The content of total nitrogen, available nitrogen, available potassium, available phosphorus and organic matter was highest in the shady slope under different slope aspect.6 Slope position has little effect on the differentiation characteristics of the soil nutrient elements at different slope aspect under the combinations of slope position-slope aspect. The available phosphorus was mostly affected by the slope aspect on the down slope. The soil nutrients were highest under a down slope and mid slope, while the slope was gentle slope and mid gentle slope under the combinations of slope position-slope. The upslope has an effect on the differentiation characteristics of the soil nutrients on the slope. Under the combinations of aspect-slope position, the content of total nitrogen, available nitrogen, available potassium and available phosphorus was significantly affected by the slope position on the shady slope. The content of organic matter was highest at the upslope of the shady slope, which was 26.60g kg-1. The effect of aspect on the soil nutrients was notable than the slope under aspect-slope. The slope also affected the soil nutrients under half-sunny slope, sunny slope and half shady slope. Under the combinations of slope-slope position, the total nitrogen and available potassium was significantly affected by slope position on the moderate slope. The available phosphorus on the steep slope was affected by slope position. The aspect on the gentle slope has a significant effect on the soil nutrients. The aspect affected the total nitrogen and organic matter on the gentle slope obviously and the available nitrogen and available potassium were notable affected by slope aspect. |
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