Temporal and spatial variability of soil organic matter and total nitrogen in an agricultural ecosystem as affected by farming practices

Abstract

In agricultural ecosystem, soil organic matter (SOM) and soil total nitrogen (STN) are important indexes in estimating the soil carbon stock, soil fertility and soil quality. This paper examines the temporal and spatial variation of SOM and STN in Rugao city, Jiangsu Province, an agricultural area in Yangtze River Delta region, China, as affected by farming practices using the data from 1982 through 1997 to 2002. Spatially, loamy Stagnic Anthrosols (Baipu) in the eastern area and clay Aquic Cambosols (Changqingsha) in the southern area had high contents of SOM and STN, whereas sandy Ustic Cambosols (Guoyuan) and Aquic Cambosols (Motou) in the mid-western areas had low SOM and STN contents, and loamy Aquic Cambosols (Banjing, Dongchen, etc.) in the northern or southern areas had medium SOM and STN contents. Temporally, SOM had shown a tendency to constantly increase in the past 20 years. During the period 1982–1997, the SOM and STN in the mid-western areas rapidly increased due to the effect of farming practices such as incorporating crop residues in soils and shifting from corn–wheat rotation to rice–wheat rotation. From 1997 to 2002, the soils in the eastern and southern areas had a rapid increase in SOM owing to the adjustment of agricultural and cropping structures and/or application of more organic fertilizers, whereas those in the mid-western areas increased slowly or even decreased because of reduced incorporation of crop residues in soils. Accordingly, STN content in the eastern and southern areas increased slightly, but soil STN content in the mid-western areas did not change or decreased in some areas. In conclusion, the incorporation of crop residues in soils and the application of organic fertilizers were effective in increasing SOM, whereas the application of organic fertilizers in combining with chemical fertilizers were effective for accumulating STN. As regards to the implementation of these sustainable measures under rapid economic development, the government must be liable for guiding or supporting farmers so that the sparse soil resources in the densely populated area can be appropriately utilized.