黑河中游临泽绿洲农田土壤有机质时空变化特征

Characteristics of spatio-temporal changes of soil organic matter in typical oasis croplands of Linze County at middle reaches of Heihe River

土壤有机质是表征土壤质量的一个重要指标，持续稳定的有机质含量是土壤维持生产能力的基础。土壤有机质的动态演变可以表征土地利用和管理水平。结合地理信息系统，运用地统计方法研究了黑河中游的临泽县绿洲农田20多年来土壤有机质含量的时空变化特征。结果表明：（1）1982年0～20cm耕层土壤有机质含量平均为12．78±4．38g／kg，2008年平均为13．76±4．02g／kg；从1982—2008年，有机质含量总体有所上升。（2）两个时期的土壤有机质的实验变异函数值与理论变异函数拟合均较好；克立格插值和不同时期的有机质空间分布图叠加运算表明，由于人为活动的影响，土壤有机质的结构性空间变化程度有所减弱。（3）临泽县土壤有机质含量和变化具有一定的区域性特点：南部的山前平原地区土壤有机质含量较高，呈现上升趋势；中部地势低下的区域土壤有机质相对较高，由于农田面积扩大，有机肥供应不足而下降显著；北部绿洲与戈壁交错带土壤有机质偏低。总体来看，临泽县土壤有机质含量有所上升，但局部地区的有机质发生了下降。为了防止局部区域土壤有机质下降引起土壤退化，应该采取加大有机肥投入和实施秸秆还田等措施。

In agricultural ecosystem, soil organic matter （SOM） is an important index in assessing the soil quality and the sustainable and steady contents of SOM is the foundation of soil productivity. The dynamic evolution of SOM is contributed to characterize the land-use and management level. In arid and semiarid region of China, the water resources and landscape changes have been mainly concerned by most of researchers; yet there are only few studies that deal with soil quality change. This paper examines the temporal and spatial variation of SOM in Linze County, an agricultural area in the middle reaches of Heihe River Basin, Gansu Province, China. Based on spatial analysis function of GIS, spatial heterogeneity of SOM and its spatio-temporal changes in the Linze oasis croplands were studied with semivariogram and ordinary Kringing showed as follows ： （ 1 ） The average concentration of SOM in topsoil of cultivated soil between the 1982 and 2008 of geostatistics. The results was 12.78 ±4.38 g/kg in 1982 and 13.76 ± 4.02 g/kg in 2008, respectively. Taken as a whole, the content of the SOM in Linze County showed increasing tendency from 1982 to 2008. （2） The exponential model was fit for both data sets in the two periods. Results of mapping of SOM by Kringing in the two periods show that the spatial structure of SOM was decreased due to the anthropogenic activities. （3） The content and features. The soil in piedmont of the south of Linze oasis contains changes of SOM in the past years showed regional higher content of SOM and have increasing tendency. The soils have relatively higher concentrations of SOM in the low terrain of the middle of Linze Oasis, but there was decreasing trend for the concentrations in that area because of increasing areas of cropland and deficiency of organic input. The soils in northern of the oasis interleaving with Gobi landscape where has low content of SOM. In conclusion, SOM had been increasing with the cultivation time in the Linze County. But the content of SOM in some regions was declined. In order to prevent SOM declination and sustain the content of soil organic matter, both measures of organic fertility input and returning straw to field should be taken to the greatest extent. With regards to the implementation of these sustainable measures under rapid economic development and the population increase, the government must be liable for guiding or supporting farmers so that the sparse soil resources in the oasis of arid region can be appropriately utilized.