黄土高原南麓县域耕地土壤速效养分时空变异

在生态脆弱的黄土高原南麓合阳县,以1983、2006年耕地土壤速效氮、磷、钾含量为对象,利用空间自相关、变异函数及分形维数等方法,研究县域土壤速效养分时空变异特征及主要影响因素.结果表明,从1983到2006年,除土壤速效钾外,耕地速效氮、磷的平均含量分别提高73.98％和92.69％;土壤速效养分全局Moran's I指数和空间相关距均呈递减变化、分维数增加,预示其空间结构减弱,随机变异性增强.土壤速效氮、磷含量在绝大部分研究区域内呈现不同程度累积,而速效钾含量则在59.65％的耕地上减少;导致其不同变化的因素有耕地利用方式、施肥管理、灌溉、土壤类型等,其中以土地利用方式和施肥管理措施的影响最大.

Temporal and spatial variability of soil available nutrients in arable Lands of Heyang County in South Loess Plateau

Soil available nutrients play important roles in ensuring high, stable yields and avoiding water eutrophication. In this study, the spatiotemporal variation of soil available nitrogen (AN), phosphorus (AP) and potassium (AK) was studied in Heyang County of Shaanxi Province, an ecologically vulnerable area at the south Loess Plateau. Two sets of data were used for analysis in this study, in which 545 and 618 soil samples data were from the second national soil survey in 1983, and Shannxi Province arable land soil fertility survey in 2006, respectively. Prior to data analysis, outliers were identified and removed. Logarithmic and BOX-COX transformations of data were performed to obtain normality distribution of variables. Data were analyzed with spatial autocorrelation, semi-variance function and fractal dimension analysis. Factors affecting soil nutrient change were identified using Kriging interpolation and zonal statistics. The results showed that mean concentrations of arable soil AN, AP and AK were 35.4, 8.2, and 195 mg/kg in 1983, respectively; whereas their average contents in 2006 were 61.5, 15.8, and 196 mg/kg, respectively. The contents of soil AN and AP were significantly increased from 1982 to 2006 by 26.2 (74.0%) and 7.6 (92.7%) mg/kg, respectively. It was found that there was significant difference between soil available nutrient contents in 1983 and those in 2006 based on the Levene's equality of variance test. Spatial autocorrelation analysis showed that the Moran's I values of AN, AP and AK in the two time points all showed spatial cluster at 0.01 significance levels. Soil available nutrients in 1983 had higher Moran's I values, indicating their stronger spatial structure. In semi-variance function and fractal dimension (FD) analysis, AN, AP and AK contents in 2006 had shorter spatial correlation distance and higher fractal dimension values, suggesting that soil available nutrients in 2006 exhibited weaker spatial structure and self-similarity. Thus, results obtained from analysis with three methods confirmed their effectiveness. The spatial patterns of soil available nutrients in 1983 and 2006 were analyzed with kriging interpolation and raster computing in ArcGIS. It was found that soil AN and AP contents in most study areas showed varying degree of increase in the past 23 years. In contrast, soil AK content decreased in 59.65% of arable land during this period. The relationships were analyzed between soil nutrient changes and land use type, fertilizer application, geomorphic type, soil type and so on. It was found that soil available nutrient changes were significantly affected by these factors. Among others, excessive N and P fertilizer use and land use change were the main reasons for soil AN and AP increase. The decrease of soil AK was due primarily to the shortage of K fertilizer.