Spatial Variability Of Soil Properties And Fertility Evaluation In Beijing Suburban Farmland

This paper combined the methods of geo-statistics and geographical information system (GIS) to do a research in the soil properties spatial characteristics and distribution of fertility parameters in North Canal Basin to evaluate the status of soil properties there, and provided the basic information for future fertility partition management and precise fertilization. Soil fertility parameters include pH, bulk density, organic matter, total nitrogen, nitrate nitrogen, available phosphorus and available potassium. And based on the standard of Beijing soil properties grading classification, drawn the maps to show the spatial distribution of soil properties grade and its area. Then analyzed the factors that affect the spatial variability of soil properties. For soil fertility evaluation, used the method of comprehensive fertility evaluation, provided a comprehensive fertility evaluation to the status of North Canal Basin soil properties. The results revealed:(1)In March and November, for 0-50cm and 50-100cm soil layer, the coefficient of variation ranged from 1.76% to 98.51% for the seven fertility parameters. pH had the lowest coefficient of variation (1%).(2) Analyzed with semi-variograms and in the isotropic level, contents of these seven kinds of soil properties in different soil layers majorly consistent with Gaussian model and the exponential model in March and November. The range of seven fertility parameters in 0-50cm and 50-100cm soil layer had significant changes within the range of 6.65km-151.55km and 18.89km-166.50km. These seven properties had relatively strong spatial correlation contents within a certain distance, which was caused by structural factor. In November, total nitrogen, phosphorus and potassium in 0-50cm soil layer has a strong spatial autocorrelation, and nugget value was within 0-19%. The organic matter and nitrate has a moderate spatial correlation, which was related to both structural and random factors.(3)The analysis of isotropy showed that in March and November their nugget value, sill value and the range are all the same in four directions in different soil layers, which indicated that fertility parameters in the four directions have banded structure with isotropic characteristics. Spatial variability is not obvious, which means this phenomenon is mainly affected by human fertilization and tillage behavior rather than the structural factors, like parent material.(4)Results showed that the soil permeability in the watershed is overall better, the soil bulk density is much higher in the northeastern basin, especially for the sporadic regional in Shunyi, which is very hard. The study area as a whole was weak alkaline soil, the soil organic matter was higher in November, but in the study area contents of organic matter were showed little bit less than the middle level. Contents of total nitrogen and nitrate nitrogen showed the same trend, in which their contents declined sharply in November. Total nitrogen and nitrate nitrogen contents showed massive distribution, the northern areas is higher than the southern. In November, contents of available phosphorus and available potassium showed somewhat higher than previous, which indicated enrichment. Taking the soil nutrient grading standards from Beijing as a reference, then all the fertility parameters contents in the study area were little bit less than the middle level.(5)Integrated fertility of the topsoil in the southeastern and southeastern is much higher, which means EFI>0.7 and is the level I area. The integrated fertility declined sharply in November after one year’s planting, the area of the first level declined from 10494 hm2 to 0 hm2. Only 0.33% of the area is in the second level, for all of Daxing District and the junction of urban and rural of Tongzhou District, where the IFI was between 0.3 and 0.5 has already declined to 0.3, from low to extremely low level. So fertility management should be area-based management. In order to improve soil fertility, more organic matter should be putted into the area which is in the low concentrated level, while in the higher concentrated level fertilization should be controlled to avoid soil enrichment and the environmental issues.