The Characteristics And Assessment On Soil Quality Of Shrub Lands In Loess Plateau

The wide planted shrub lands of soil and water conservation in Loess Plateau can prevent soil and water loss and have important effect on both revegetation and the ecological environment construction. This research aimed at the soil quality problem of shrub lands, took three kinds of shrub lands as research object as below: the Caragana Korshinskii Kom. Land (CKK) of Shanghuang experimental field in Gu yuan City, Ningxia Hui Autonomous Region,the Hippophae Rhamnoides L. land (HRL) of Gaoquangou watershed in Dingxi City, Gansu province and the Natural Secondary Forest land (NSF) of Feimahe watershed in Yan'an City, Shaanxi province. This thesis systematically researched the basic feature, the vertical and horizontal distribution, indicator system and comprehensive assessment of soil quality by soil sample collection, field investigation, laboratory analysis on soil physical, chemical and soil enzyme indicators, and statistic methods of variance analysis, correlation analysis, factor analysis and stepwise regression analysis. The main results were as follow:1. The change trend of sand and silt particle content of the three shrub lands on different slope aspect is shady slope>half sunny slope>sunny slope, and clay particle content is shady slope>half sunny slope>sunny slope; the difference of sand and silt particle content on different slope position is upper>middle>lower position of slope, and contrary sequence for clay particle content. The soil aggregate content on the upper position of slope>middle>lower position of slope, and it showed shady slope>sunny slope>half sunny slope on different slope aspect. The improve effect sequence of shrub lands on siol aggregate is HRL>CKK>NSF. Compare with 10 years old CKK, the 20 years old ones had less sand particle and more silt and clay content, this showed the soil has a little changed to fine soil. The total soil aggregate content, mean weight diameter and the soil aggregate content of different diameter all increased a little. The Bulk Density of shrub lands increased by the depth increase on the soil profile and the improve sequence is HRL>CKK>NSF.2. The content of organic matter (OM), total N (TN), alkali-hydrolyzed nitrogen (AHN), available K(AK), CEC, and CaCO₃ in the topsoil of shrub lands is mostly"middle"level except AHN of CKK and NSF is"lower"level, AK of NSF is"sub-high"level, CEC of CKK is"lower"level, CaCO₃ of CKK is"high"level. The total P (TP) content of CKK and HRL is"high"level and NSF is"sub-high"level; and the available P (AP) of three shrub lands is"much lower"level, at the same time, the total K of three shrub lands is"sub-high"level.The content of OM, CaCO₃,AK and EC of the topsoil of three shrub lands decreased by the increase of soil depth on the profile, and there are significant differences between the different soil layers. On the other hand, the content of TN, AHN and TK showed no significant difference on the profile.The OM and TN content of the topsoil showed same distribution regular pattern, that is upperhalf sunny slope>sunny slope between different slope aspects, but AHN didn't show the same trend. Meanwhile, the content of TK and AK showed no significant difference between both different slope positions and different slope aspects.Compare with 10 years old CKK, the 20 years old ones had less TP, AP, CaCO₃ and lower pH, but had more OM, TN, AHN, AK, CEC and EC. In a word, the soil nutrition contents and soil quality will improve with the increase of age of shrubs.3. The activity sequence of phosphatase and Invertase of the topsoil of three shrub lands is CKK>HRL>NSF, but it is CKK>NSF>HRL for urease. Slope aspects had no notability influence on soil enzyme activities but the slope positions obviously influenced the soil enzyme activities, the enzyme activities of the upper slope positions are generally higher than lower slope positions. The soil enzyme activities enhanced as the tree ages increasing and fell down as the depth of soil profile increasing.4. It showed very significant correlation between most of physical features of the researched 15 physical properties, and also for the researched 12 chemical properties except coarse clay particle, fine and Coarse silt particle and water content. The fine clay particle, fine silt particle, fine sand particle and OM had significant improvement on the nutrition conservation and soil quality enhancement. It showed very significant correlation between the soil enzyme (urease, phosphatase, Invertase) activities of three shrub lands.5. The simple assessing indicator system of 9 indicators for soil quality had been ascertained for the shrub lands on Loess Plateau: OM, TN, TP, TK, AHN, Invertase activities, CEC, CaCO₃ and water content. The assessing model had been established and was used to assess the soil quality of the three shrub lands. The result showed the soil quality sequence is HRL>CKK>NSF. The soil quality of HRL is gradeâ…¡, but the quality of CKK and NSF is gradeâ…¢. The best shrub type should be HRL when we plant shrub in Loess Plateau, the second should be CKK, and the last one should be NSF. The soil quality of the three shrub lands was obviously different on the soil profile, decreasing with the soil depth increase, and there were significant difference between different soil layers on the profile. The soil quality of different slope position had no significant difference, but that of different slope aspects was shady slope>half sunny slope>sunny slope. The soil quality improved with the increase of shrub ages.