Soil Nitrogen Stocks And Its Spatial Distribution In Zhejiang Province

As an important component and a vital factor either in global nitrogen pool or ecosystem, soil nitrogen has always been attracting great attentions on agriculture, ecology, soil and environment science, and now has become the hot topic of global change research. As an important part of China soil nitrogen pool, the estimation of Zhejiang soil nitrogen pool is of great significance to national and regional agriculture, ecology and environment. By using Zhejiang1:50000soil database, the spatial analysis techonolgy of GIS, the soil total nitrogen(STN) density and stocks in the0-20cm and0-100cm layers in Zhejiang province was estimated,as well as the spatial distribution of the STN were analyzed in this study. The main results are as follows.The estimation of STN densities and stocks:the average STN density of Zhejiang province in0-20cm and0-100cm soil layers is0.30kg/m2and0.85kg/m2; and the stocks of two layers are29.9×106t and85.4×106t. The STN densities and stocks of10soil groups,21soil subgroups,99soil genus and277soil species in the0-20cm and0-100cm layers were respectively analyzed, and a huge gap was found between different soil types. And among all soil species, the maximum STN density in0-20cm layer is30times bigger than the minimum value, while the gap of STN stocks between the maximum and minimum value in0-100cm layer reached about61000times. Mountain meadow soil in Zhejiang soil always has the highest STN density in soil groups, subgroups, genus and species, while in which different soil have the minimum STN values. In comparision of STN stocks between different soil types, it shows that the STN stocks were largely determined by the soil areas. Of all the cities in Zhejiang province, Jiaxing has the highest STN density both in the0-20cm and0-100cm layers (0.37kg/m2and1.34kg/m2respectively), while Jinhua has the lowest STN density in each of layers (0.21kg/m2and0.62kg/m2respectively). Lishui and Hangzhou have the biggest STN stocks respectively in0-20cm and0-100cm soil layers (5.56×106t and1.59×106t), while Zhoushan has the lowest STN stocks in two layers (294.2×103t and841.1X103t)As the important environmental factor and foundmental material of soil formation, terrain and soil parent materials largely determined soil properities and spatial pattern. In this study, Zhejiang was divided into7landform areas, and the accumulational landform region has a very high STN density both in0-20cm and0-100cm soil layers, the erosion-denudational landform region has a very low STN density both in0-20cm and0-100cm soil layers, the tectonic-erosional landform region either has a high STN density in0-20cm soil layer or a low STN density in0-100cm soil layer,while the coastal landform is contrary to the tectonic-erosional landform region. With the elevation escalating, The STN density in Tianmu mountain area first decreased gently and then increased rapidly, and the turning point just appeared at the600meters elevation region where the red soil seperates from yellow soil. With the solpe escalating, the STN density in0-100cm laye shows a sharp decrease firstly, and then maintained stable, finally kept a gent decrease. While the STN density in0-20cm layer shows a different trend in the>25°slope area, it increased slowly first and then decreased with the escalation of slope. As for the average STN density in different parent material areas, the result shows that the limnetic material region and the residual-talus material region have the hightest and lowest STN densities respectively. The STN in Qiantang basin was studied by dividing it into17soil buffer zones, the average STN density for each zone existed a general negative correlation with red soil (r=-0.421), a general positive correlation (r=0.514) with paddy soil, and a significant negative correlation(r=0.815) with yellow soil.