岩溶区坡耕地土壤肥力综合评价——以重庆中梁山坡耕地样区为例

Soil fertility evaluation of slope farmland in karst area:A case study of slope farmland in Zhongliang mountain in Chongqing

坡耕地是我国西南地区最重要的土地利用类型,也是我国一项重要的国土资源。由于该地区坡耕地石漠化程度高,土壤侵蚀问题严重,致使坡耕地土壤肥力不断退化。以重庆市中梁山坡耕地样区为例,采用模糊综合指数法进行小尺度坡耕地土壤肥力评价。经取样数合理性分析表明,25个样点估计研究区土壤肥力评价能够满足90%置信水平条件下,10%、15%和20%的相对误差取样数的精度要求;运用主成分分析（PCA）,通过计算变量的Norm值筛选有机质、全氮、全磷、全钾、碱解氨、耕层厚度和粉黏比进入最小数据集（MDS）,并对进入MDS的肥力因子进行相关系数分析检验,表明选取的MDS能最大程度表达坡耕地土壤属性信息;利用隶属度函数实现评价指标量纲归一化并对单项肥力指标进行评价,采用加权求和模型计算土壤肥力综合指数（IFI）,结果表明,土壤有机质和全磷是影响研究区土壤肥力的限制因子,研究区80%样地肥力综合指数在0.40-0.60之间,肥力水平处于中等程度。

Slope farmland is one of the main land-use types in southwest China,and also an important farm land resource in China.However,rocky desertification and soil erosion problems are serious in slope farmland areas,leading to soil fertility degradation.Taking Zhongliang mountain in Chongqing as a case,the soil fertility of slope farmland was evaluated on a small scale by the fuzzy comprehensive index method.According to statistical analysis of sample number rationality,the regional soil fertility evaluation based on 25 soil samples was sufficient to meet the required accuracy of 10%,15%and 20%relative error at a 90%confidence level.The minimum data set（MDS） components including soil organic matter,total nitrogen,total phosphorus,total potassium,available nitrogen,soil depth and silt/clay were selected by calculating the norm values based on principal components analysis（PCA）.Correlation coefficient test between the indicators inside MDS showed that MDS represented maximally all the soil properties with minimal loss of soil fertility information.Membership function was used to transform the indicators into dimensionless data and a weighted summation model was used to calculate the integrated fertility index（IFI）.The membership values and IFI reflect the single factor fertility and the integral fertility respectively.This indicated that soil organic matter and total phosphorus were the limiting factors for the soil fertility in the study area,and soil integral fertility was at a medium level with integrated fertility index（IFI） ranging from 0.40 to 0.60.