The Study On Soil Fertility And Quality Under The Different Landform And Land-Use In Gully Region Of The Loess Plateau

Changwu County is located in the South of the loess plateau,there was the transition zone of conjunction that Weibei and Gansu Plateau. The region's climate type is humid continental warm temperate monsoon climate, Average annual rainfall was 584mm, mean annual temperature was 9.1oC, A typical dry farming district. Its'geomorphology is a gully region of the loess plateau. The plateau and gully coexist in this region. There are three main types of land including the plateau, slope, gully. It was the region of severe soil and water loss. Before 1980, that mainly to grow food in this region, Then part of the farmland has turned into orchards, There occurred transformation of the conversion by Food-base to Food-Fruit base on the Loess Plateau, At present, this region has become an important production base of apple. The change of land-use, will definitely cause the changes of soil fertility and quality, this problem attracts the most attention.In order to make clear the the process of dynamic change of soil fertility and land quality degradation mechanism which in the process of This study reached the following conclusions by measurement and analysison of soil organic matter, nutrients and trace elements in different landform (plateauland,slopingland and floodland)and land-use (orchard and farmland)in northern part of ChangWu County.Meanwhile, We assessed comprehensively the soil quality of entire region.The following important conclusions and progress made:(1) The SOM content is 5.2g/kg~18.1g/kg in northern area of Chang wu County, the average content is 11.7g/kg.The content of soil organic matter has achieved the medium fertility level of this area. The content to be different levels of soil organic matter and soil active organic matter in different landform.The plateauland(12.77g/kg) was relatively higher than the floodland(9.56g/kg) and the slopingland(11.93 g/kg),also the different Land-use affects the content change of SOM and SAM, the content of SOM and SAM of orchard was slightly higher than the farmland soil, the orchard upper layer is higher than the lower layer; Along with fruit tree age's increase, the SOM and SAM to be droped.(2) The TN content of this area ranges from 0.6g/kg to1.3g/kg,the overall average was 1.0g/kg . the average content of AN was44mg/kg.Soil total nitrogen achieves the medium fertility level of the whole areas. The orchard soil total nitrogen achieves the higher fertility level, the farmland reaches on the medium level. The different terrain to TN and AN's influence also slightly has the difference, the TN (1.02 g/kg)and AN (47.88 mg/kg)of plateauland were relatively higher than the floodland's(0.85 g/kg,38.76 mg/kg) and the slopingland's(0.95 g/kg,41.18 mg/kg); The different Land-use to TN and AN's influence also slightly has the difference,To be compared with the TN, AN content of farmland,The TN, AN content of orchard surface soil was increased by more than 9%, 5%. With the increasing of orchard planting ages, the TN and AN assumed the declining trend in upper (0-20cm)and lower(20-40cm) layer of orchard.(3) The overall average contenr of TP,AP as 0.9g/kg, 16.3g/kg.The AP reached on the middle fertility levels. The AP of orchard achieved high fertility soils, the farmland in general reached to the middle soil fertility level; Under different landforms, the TP and AP content of plateauland were higher than the floodland and slopes. The different Land-use patterns, the TP content of upper orchard was slightly higher than the farmland, the AP content of upper orchard was higher than the farmland more than twice as high.With the increase of years of orchards, the TP and AP content occurred the cumulative effect in the upper and lower layer, that was reached maximum content on 5-15 years of the orchard.(4) The area of soil potassium changes in 16.7g/kg ~ 25.1g/kg,the overall average was 21.3g/kg, The area of soil AK changes from 63.1 mg/kg to 438.7mg/kg,average content of AK was 217.8mg/kg, The AK in the region reached a high fertility levels (>150mg/kg). The AK content of orchard and farmland have reached higher levels;The TK in different terrain positions did not have significant differences, the TK of orchard and farmland soil were significantly higher.The TK content of the plateauland (21.48 g/kg)compared to the floodland (21.23 g/kg) and slopingland (21.00 g/kg) is more higher. The AK content of orchard were slightly higher than the farmland (increased 27%). With the increase of years of orchard planting, The AK content was gradual increase in surface of orchard, The AK content of 15 years,5-15 years compared with <5 years increased by 31.5%, 39.6%, The AK was increased more in the prosperous period.(5) The overall average content of trace element in soil, Fe: 5.89mg/kg, Mn: 19.8 mg / kg, Cu: 0.9mg/kg, Zn: 0.91mg/kg,The Mn achieves the higher fertility level. Landform influenced the distribution of soil trace element.The content of soil trace element(Fe,Mn,Cu) shows trends that plateauland > slopingland>floodland. However,Zn has relatively high level in floodland.Under the different land-use, the trace element average content of orchard was higher than the farmland, The different land-use have the significance difference differently. Along with increase of planting age, The soil trace element presents the cumulative effection in the upper and lower layer of orchard(5-15years). (6) The distribution of soil TN,AN changes as the parabola along the Jinghe River basin from east to west, The TN,AN content of middle area were more higher and the eastern regions was the lowest. The TP was highest in Western and lowest in eastern regions. The distribution of soil AP changes as the parabola, The AP content of middle area were more higher and the eastern regions was the lowest. The distribution of soil TK,AK changes as the parabola, The content of TK,AK in the middle area was relatively high. The distribution of soil trace elements changes as the parabola .Considered that the distributed situation of different landform,There has three kinds approximately: From east to west, the tendency of SOM and SAM to be consistent in different landform, that Assumes parabola distribution completely , the distribution of soil nutritive elements was different in different terrain spot. And the distribution of the floodland is most complex and the regularity is not strong, the phosphorus and the potassium content was rich, the phosphorus and the potassium content's distribution in the slopingland and plateauland was averaged,and the scope is not big . The trends of soil trace elementin floodland was changed as the same straight line, The distribution of the slopingland and plateauland changes as the parabola.(7) Through the method of principal components and Norm value to determine the soil quality evaluation of the minimum data set MDS,Eventually there were 12 indicators enzymes into the minimum data sets of this area soil quality evaluation, which are the SAM,TN,AP,AK,Clay, CEC, Fe, Cu, Zn, Catalase, Phosphatase, and Invertase and so on. by the two evaluation methods of partial correlation and principal component to determined soil factor weight, and through the application of fuzzy mathematics model to computate the soil quality evaluation index FQI under different terrain spot and the different land-use,The results show that, Index of soil quality in the region FQI values ranged from 0.25-0.7, most of soil concentrated in between 0.5-0.7, so the overall soil quality in the region are the middle class. By the membership of the soil factors, that the SOM,TN, AN, AP and AK and Cu, Zn are the limiting factors of local soil quality development, Moreover soil quality index was indicated by these two kinds of method of weighting definition:soil quality of orchard is better than farmland, soil quality of plateauland was first,the slopingland second, the floodland was worst;As the increasing of orchard planting ages, soil quality is not significantly increase or decrease .