| The ecological environment of loess hilly areas is fragile,which it leads to soil erosion,land desertification,drought and floods.The special geographical position vulnerable to wind erosion,not only effect the local economic development,ecological security and people's life,but also seriously threaten downstream plain areas.However,the improvement of ecological environment is imperative,and returning farmland to forest and grass is the basic measure to control soil erosion on the Loess Plateau.The soil physical and chemical properties such as soil bulk density,soil cohesive force and soil nutrient was changed after the implementation of the project of returning farmland to forest and grass.This project provide theoretical basis for soil remediation,and it has great significance to the comprehensive management of soil erosion in the Loess Plateau.In this paper,through data collection,field investigation and sampling analysis,we study the change of soil physical and chemical properties in loess hilly region by Geostatistical method.The soil physical and chemical properties of the cultivated land area and enclosed area(Returning farmland area)were analyzed as well as variation tendency.Based on the change of soil surface,the difference and change regulation of soil properties was analyzed and summarized.The conclusions are as follows:(1)The soil water content of the enclosed area was 0.6% higher than that in the cultivated land area.This due to the high surface vegetation coverage could reduce the rainfall runoff and surface evaporation in enclosed area,and the cultivated land was just the opposite.In addition,the herbaceous root system in the enclosed area was relatively deep,and the root mainly absorbed the lower layer of water,resulting in more soil moisture in the upper of soil profile.(2)The soil bulk density of the cultivated land area increased by 0.01g/cm3 compared with the enclosed area,and the soil porosity of the cultivated land area increased by 1% compared with the enclosed area.Due to the large number of herbaceous root in the enclosed area,the soil particles were pulverized and the soil porosity increased and the bulk density reduced.On the other hand,herbaceous plants litter in the topsoil was easy to decompose and form soil organic matter,and it was directly reducing the soil bulk density.Second,the less compacted soil pores in cultivated land area thanks to the influence of human activity,so the soil bulk density was relatively high.(3)The average content of soil organic matter was 9.65g/kg and 10.2g/kg in cultivated land and enclosure area,respectively.The soil organic matter content in enclosed area was 5.7% higher than that in cultivated land area.Compared with the enclosed area,the soil organic matter in the cultivated land area was low.It was due to the lack physical protection of organic matter and increases the soil temperature in the cultivated land soil.Soil mixing with organic residues increased the activity of microorganisms,and increases the decomposition rate of organic matter.(4)The average content of total nitrogen was 0.32g/kg and 0.29g/kg in the cultivated land area and the enclosed area,respectively.The soil total nitrogen content in the cultivated land area was 10.34% higher than that in the enclosed area.Soil total nitrogen content was also closely related to soil type.In the study area,the soil is chestnut soil.The soil erosion is serious,making the soil barren.The organic matter content was very low,so the total nitrogen content was low.With the increase of cultivated land degradation,soil total nitrogen content will decline rapidly.(5)The average value of total phosphorus was 0.52g/kg and 0.42g/kg in cultivated land area and the enclosed,respectively.The soil total phosphorus content in the cultivated land area was 23.8% higher than that in the enclosed area.The soil total phosphorus content was diminishing appeared in the second layer in the enclosed area and the cultivated land area,which may be due to the better absorption of phosphorus in the 5~10 cm soil layer by the plant(crop)root system.(6)The average value of total potassium was 3.43g/kg and 3.23g/kg in the enclosure and the cultivated land area,respectively.The total potassium content in the enclosed area was 6.19% higher than that in the cultivated land area.In general,the total potassium content was increasing and decreasing trend in enclosed area and cultivated land area,respectively.It may be related to the decrease of organic matter distribution and the initial soil parent material and the role of soil formation.(7)The average content of soil available nitrogen was 0.12mg/kg and 0.04mg/kg in cultivated land area and enclosed area,respectively.The soil available nitrogen content in the cultivated land area is higher than that in the enclosed area,which indicates that the soil nitrogen supply potential in the cultivated land area is better than that in the enclosed area.(8)The average content of available phosphorus was 10.28mg/kg and 65.51mg/kg in the enclosed area and the cultivated land area,respectively.It can be seen that the soil available phosphorus content in the cultivated area is higher than that in the enclosed area,which may be related to the implementation of the phosphate fertilizer in the cultivated land area.However,the change of available phosphorus content was closely related to vegetation root uptake,leaching loss,phosphorus content in sediments and decomposition rate of sticky soil.(9)The average content of soil available potassium was 13.02mg/kg and 21.17mg/kg in cultivated area and enclosed area,respectively.The available potassium content in enclosed area was 62.6%.higher than that in cultivated land area.The available potassium content in the cultivated area was low,because the available potassium of the soil mainly relies on the decomposition of the vegetation litter to be compensated.The crops in the cultivated land area was single and the litter was less and the decomposition rate was slow,so that absorption rate of crop root system was greater than compensation rate of available potassium of vegetation litter. |
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