Effects Of Land Use And Topographic Factors On Soil Nutrients Variability In Mountain Area

As a natural resource，soil is an important part of terrestrial ecosystem and themost basic means of production of agroforestry. Soil nutrient provide the necessarynutrients for plant growth, and it is the important factor influencing soil health andecosystem productivity. Topographical factors influent soil development stage anddegree by affecting hydrothermal conditions and material redistribution; Humanactivities changed the soil environment directly or indirectly, which affecting thespatial distribution of soil properties. In an area, topographical factors and the way ofland use respectively represent internal forces and external forces that affecting thesoil nutrient content and spatial distribution, and they act on surface soil at the sametime.Take Qixia for example, with the help of mathematical statistics andgeostatistics, using computer and GIS technology, this paper studied the semivariablefunction and its theoretical model of the organic matter, total nitrogen, totalphosphorus and total potassium in surface soil; analyzed the law of spatial variabilityof soil nutrients. In addition, this paper discussed the correlations between soilnutrient content and altitude, slope, aspect and land use type; analyzed thecharacteristics of four kinds of soil nutrients, under different topographical factors anddifferent land use type. Considering the characteristics of hilly area, this paper furtherin-depth discuss the effects on soil nutrients by the interaction of topographical factorsand land use type. The main results are as follows:（1）Descriptive statistical characteristic and semi-variance function analysis ofsoil nutrients. With the variation coefficient vary from22.49%to40.63%, the fourkinds of soil nutrient all belong to moderate variability, and order of the variability isas follows: organic matter> total phosphorus> total nitrogen> total potassium. Byanalysising semi-variance function, the theoretical model of the soil organic matter,total nitrogen, total phosphorus and total potassium are respectively: Spherical Model, Gaussian Model, Gaussian Model and Exponential Model. The nugget effect of totalphosphorus is greater than75%, which shows that the soil total phosphorus withweaker spatial correlation is mainly affected by random factors. While the nuggeteffect of organic matter, total nitrogen and total potassium is between25%~75%,suggestting that these three kinds of soil nutrient are affected by structural factors andrandom factors at the same time, and they have medium spatial correlation. Thenugget effect of organic matter and total potassium are less than50%, which meansstructural factors play a dominant role. While the nugget effect of total nitrogen ismore than50%, meaning random factors play a dominant role.（2）Spatial distribution characteristics of soil nutrient. Comparing the spatialdistribution figures of four kinds of soil nutrient: Having similar spatial distribution,on the whole in block distribution, In the northeast the soil organic matter and totalnitrogen content is higher than that in the southwest, besides their high value area andlow value area are basically identical. Similar to organic matter and total nitrogen, onthe whole in block distribution, soil total phosphorus is higher in the study area, andmainly distributed in the northwest, northeast and south. The content of totalpotassium in the study area is rich, which is higher in the north than in the south, andit is in zonal distribution along the border in the southeast northwest four directions.（3）The relationship between topographical factors and soil nutrients. Thealtitude and slope factor have a strong correlation with soil nutrients, but thecorrelation degree of aspect and soil nutrients is low. The altitude and slope factorhave very significant positive correlation with the content of soil organic matter andtotal nitrogen, with the increace of altitude and slope, the content of organic matterand total nitrogen increase significantly, however the total phosphorus and totalpotassium showed a trend of decrease, but not significant. The negative correlationbetween aspect and soil nutrients is not significant. In addition to the total potassium,the average content of soil organic matter, total nitrogen and total phosphorus aremore in the shady slope than in the sunny slope.（4）The relationship between land use type and soil nutrients. According to theconfficient of variation, the order of the influence on soil nutrients by land use type is: organic matter(C.V.=41.16%)> total phosphorus(C.V.=35.14)>total nitrogen(C.V.=32.95)> total potassium(C.V.=23.03%). It can be seen that land use type have arelatively large impact on organic matter, a relatively small impact on the totalpotassium, and its influence on total phosphorus and total nitrogen are basically thesame. Soil organic matter and total nitrogen have the same content law: unused land>grass land> forest land> cultivated land> garden land. Soil total phosphorus andtotal potassium content have the characteristics: forest land and grass land> gardenland and unused land.（5）The influence of interaction between topographical factors and land use typeon soil nutrients. The interaction have different degree of influence on organic matter,total nitrogen, total phosphorus and total potassium, but most of the effects is notsignificant, only the interaction on soil total phosphorus which is between slope andland use is remarkable. Under the different topographical conditions and differentland use ways, the average content level of organic matter, total nitrogen, totalphosphorus and total potassium have differences, but the law is not obvious. It can beseen that on the shady slope with higher altitude and larger slope, the content oforganic matter and total nitrogen are higher in forest land and grass land than in thecultivated land and garden land; however the situation is the opposite on sunny slopewith lower altitude and minor slope.