Soil Nutrient Study Based On Digital Terrain Analysis (DTA)

At present, with the rapid development of the computer technology and GIS, digital elevation model (DEM) has made breakthrough progress in obtaining data methods, data processing speed and so on. Using DEM as information source to extract various terrain quantitative factors, the digital terrain analysis method has covered many subjects.Yongxing County located in the innumerable mountain of Chongqing. Its complicated variety terrain will affect the soil moisture, heat and air distribution status of soil, which will affect physical and chemical properties of soil. It is realistic significance for agricultural production to research on the influence of terrain factors on soil properties and arable land.This paper, based DEM as data sources, using statistical methods, combining GIS spatial analysis principle, digital terrain analysis method and the data processing, study and analysis soil chemical characteristics of cultivated land county. The specific content of research and the main conclusions obtained as follows:(1) Descriptive statistics of study area 618 sampling eight indexes results show: pH, organic matter, alkali-hydro nitrogen, effective phosphorus, rapidly-available potassium, total nitrogen, total phosphorus and total potassium content change range are respectively:4.1～8.6,5.3～2.38 g/kg,17.5～193.5 mg/kg,1.0～40.0 mg/kg. 20.0～280.0mg/kg,0.16～1.61 g/kg,0.01～1.02 g/kg,10.1～34.4 g/kg. From the perspective of variation coefficient of variation, all nutrients are medium variations, variability size order:effective phosphorus> rapidly-available> total phosphorus> organic matter> alkali-hydro nitrogen> total nitrogen> total potassium> pH.(2) Soil chemical properties half variance function fitting:pH, rapidly-available potassium, effective phosphorus, total potassium belongs to the exponent model, others belongs to spherical model. Half variance analysis shows that, the whole area studied nugget proportion C0/(C0+C) is for little change, distribution interval is 0.714 0.818. It is indicated soil properties of study area has been enormously influenced by random factors (such as variable experimental errors, fertilization, the management level, etc), and variable spatial correlation is very weak.(3) Using kriging spatial interpolation method and in combination with the soil nutrient classification criteria of secondary census, rendered various soil nutrient spatial interpolation charts of study area and analyzed nutrient content and spatial distribution status for different levels. Looking from space distribution pattern, in the study area most nutrient is block distribution. From different levels nutrients content distribution situation, the nutrient content distribution is very different from different nutrient. Except total phosphorus is low, and other nutrients are in the medium level.(4) Using Pearson correlation algorithm in SPSS, studied the correlation between slope, aspect, elevation and pH, organic matter, alkali-hydro nitrogen, effective phosphorus, rapidly-available potassium, total nitrogen, total phosphorus, total potassium. The results showed that the correlation between slope, elevation and nutrients is higher than that between aspects and nutrients.(5) Studied soil nutrients distribution to different slope, slopes, elevation, and variation trend with them. The results showed that the soil nutrient content increases with the trend of slope reduced in the whole point of view. Different aspects, nutrient content distribution are relatively diversification. In the study area, within the scope of elevation 328m to 238m, the nutrients changes with the elevations showed the same trend:with the increase of elevations, nutrients reduce after the first increases; and nutrient is different while the altitude of maximum nutrient is difference.(6) Extracted dry land and the paddy of research area in ArcGIS and studied soil nutrient change status of dry land and the paddy with different slope, different slopes, and different elevations. Farmland nutrient research based on the slope shows that: overall, the nutrient content of the paddy fields is more than that of dry land. Aspects paddy soil nutrient maximum focus on north and northeast, while that of dry land focus on north and east aspects. Compared the same nutrient of the same altitude between the paddy and dry land, except the total phosphorus, nutrients content in the paddy fields is higher than that dry land; In aspect of variation amplitude, the variation amplitude of nutrient with elevation in paddy field is bigger than that in dry land.