| Due to human activities,the spatial distribution and storage of total nitrogen in farmland soil are very complex.Making use of soil database to quickly and effectively obtain the basic data of soil total nitrogen storages estimation under large regional scale,which is of significance to the establishment of nitrogen management measures at large regional scale.Therefore,this study explored the spatial distribution characteristics and storage conditions of soil total nitrogen density in the top soil(0-20 cm)of farmland in Sichuan Province by excavating existing data,based on the establishment of a 1:100 0000SOTER database in Sichuan Province,and the influence factors of regional soil nitrogen reserves distribution was analyzed.The main results are as follows:(1)The digital elevation model of Sichuan Province was established adopting the method of weighted optimal fusion DEM.Based on this,the terrain data such as elevation,slope,and relief were extracted,and the 12 types of landforms were classified according to the features of Sichuan topography and geomorphology.We build the terrain unit of Sichuan Province and classified terrain species based on the principle of building database to build the SOTER unit map of Sichuan Province,and complete the establishment of SOTER database in Sichuan Province combined with existing data of topography,soil,land use and climate,etc.(2)The total nitrogen density in top soil of provincial farmland was concentrated between 0.05-0.80 kg/m~2,and the average total nitrogen density of farmland soil in each ecological area was the highest in the Northwest Plateau of Sichuan Province(0.570kg/m~2),and the lowest in the siltstones hilly(0.287 kg/m~2).The spatial distribution trend of total nitrogen density in top soil of provincial farmland was complex,and the ecological regions had obvious regional characteristics,which were closely related to the terrain,climate,soil matrix,soil texture and human activities.By comparing the performance of the model,it was found that the total nitrogen density GWR model of farmland soil in each ecological area can fit more details,and the prediction effect was better.(3)The total nitrogen storage in top soil provincial farmland was 33.80 Tg,and its spatial distribution had obvious regional differences.The highest total nitrogen storage in top soil of farmland of siltstones hilly was 18.24 Tg,accounting for 53.97%of the Sichuan Province’s total storage.Followed by Penzhou mountain(5.71 Tg),accounting for 16.90%of the Sichuan Province’s total storage.And the soil total nitrogen storage in Penzhou mountain is high and the farmland is widely distributed,its nitrogen accumulation capacity plays an important role in improving the soil nitrogen pool level in the whole province.The total nitrogen storage of dryland soil was the highest(18.05 Tg)among different farmland types,mainly due to the 55.37%of the farmland area in the province.Among different soil types,purple soil had the highest soil total nitrogen storage(16.00 Tg),accounting for 47.33%of the total storage of farmland in the province,and the total nitrogen storage of the calcareous purple soil account for 25.34%.The second was the paddy soil(10.43 Tg),and give priority to permeable paddy soil and waterloggogenic paddy soil(6.89 Tg and 1.77 Tg,respectively).The third was the yellow soil,accounting for 8.35%of the province’s total storage,which was given priority to subgroup yellow soil,proportion of storage in 6.58%.The large area of purple soil resulted in the highest total nitrogen storage,but its total nitrogen density was lower than that of paddy soil,indicating that the nitrogen storage capacity of purple soil was insufficient.(4)The ANOVA analysis showed that the top soil total nitrogen storage under different elevation,slope,slope direction and parent material reached significant or extremely significant level.The top soil total nitrogen storage rising along with the elevation of different changes,and decreased with the increase of the slope.The top soil total nitrogen storage was higher in semi-sunny slope,semi-shady slope,and shady slope among different slope directions.The total nitrogen storage was the highest in the soil developed by the loess parent material.The total nitrogen storage in soil developed by wash,glacial water and ancient river bed sediments was significantly higher than that that of residual purple rock weathering.The spatial distribution of top soil total nitrogen storage is influenced by many factors,such as terrain and parent material. |
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