The spatial-temporal variability of soil organic matter and its influencing factors in suburban area of Beijing

Chinese. 揭示土壤有机质时空变化规律及其影响因素，为土壤肥力评价和管理提供指导。通过收集和实测北京南郊―大兴区1980、1990和2000年3个不同时期耕层土壤有机质含量的资料，应用地统计学方法对其进行分析。3个时期土壤有机质的平均含量分别为9.64、12.76和12.89 g/kg，它们的空间相关距离分别为80.5、59.2和49.0 km，呈递减趋势。大兴区土壤有机质含量空间分布呈北高南低之势。从1980年到2000年，有机质含量表现为由低向高逐级累积的规律，具体变化为有机质含量一级和二级的土地面积从无增加到分别占土地总面积的8.0%和14.3%，含量三级的土地面积从23.0%增加到37.1%，四级土地面积减少很少，约为2.19%，五级土地面积减少幅度最大，为50.4%。秸秆还田和施用有机肥是有机质含量普遍上升的原因，随着作物产量的不断提高，部分地区的有机质入不敷出，呈下降的趋势，应注意土壤的培肥管理。

English. The objective of this study was to explore the spatial-temporal variability of soil organic matter (SOM) and its influencing factors, and to provide a firm scientific foundation for soil fertility assessment and management. SOM content in arable layer in 1980, 1990 and 2000 in Daxing County of Beijing was obtained by collecting data in the Second National Soil Survey (SNSS) and recent measures. The general statistics and geostatistics methods were used to analyze the data. The average SOM content at different times were 9.64 g/kg, 12.76 g/kg and 12.69 g/kg, respectively. The semivariance analysis showed that their spatial correlation distances at different times were 80.5 km, 59.2 km and 49.0 km, respectively, showing a descending trend. Kriging method was applied to estimate the unobserved points and as a result SOM content contour maps were derived, and the map indicated a decreasing trend from north to south across the county for SOM content. The SOM content had been classified into six categories (bellow 6, 6 to10, 10 to 12, 12 to 15, 15 to 20 and above 20 g/kg) according to the standards set by SNSS. The SOM changed slowly from low to high category based on the accumulation of SOM in the low category from 1980 to 2000. During the last 20 years, the area with the highest and the second highest category of SOM content changed from 0 to 8.0% and 14.3% of the total area. The area with the third category for SOM content increased from 23.0% to 37.1% of the total area, respectively. The area with the forth category for SOM content decreased little, about 2.19% of the total area. The area with the fifth category for SOM content decreased sharply, about 50.4% of the total area. SOM content increasing trend might be attribute to the widespread practices of mulching and organic manure application. With the yield improvement, some regions have exhibited SOM deficit and attention should be paid to the fertilization of SOM.