Benefits of SOM in Agroecosystems: The Case of China - Soil Carbon: Science, Management and Policy for Multiple Benefits - page 314

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Benefits of SOM in Agroecosystems:
The Case of China

Genxing Pan*, Lianqing Li, Jufeng Zheng, Kun Cheng,
Xuhui Zhang, Jinwei Zheng and Zichuan Li

Abstract
While soil organic matter (SOM) content can be directly correlated with crop yield at the country/
province level, abundance in SOM content may also be linked to economical output such as gross
domestic production per capita at the county or province scale. Benefits of SOM include increasing
nitrogen (N) efficiency, enhancing soil biodiversity and the health of soil food web systems, as well
as aiding the degradation of toxic pollutants. Among these, the enhancement of the soil microbial
community, and hence microbiochemical functions, is of key importance for productivity in crop-
lands. Many studies have shown that the metabolic quotient of the soil microbial community (the
specific quotient of soil respiration to SOM content) is unchanged or lowered as SOM accumulates.
In order to characterize these benefits, several parameters are needed: (i) microbial abundance on
the base of SOM content (microbial quotient, %); (ii) soil basal respiration to microbial biomass
carbon (C); and (iii) normalized enzyme activity on the bases of soil microbial biomass carbon and
soil organic carbon. As yet, there is no evidence that there is an SOM limit for Asian agricultural
soils. A conceptual model of the role of SOM and benefits from the interaction with mineral par-
ticles and the formation of aggregates is hypothesized to gain an understanding of the benefits of
SOM in croplands.

The Importance of Soil Organic
Matter in China's Agriculture

content has been suggested as the most im-
portant key soil quality parameter for the
European Union's (EU) agricultural and for-
estry sectors (EC, 2002). A case study of
tropical farming systems (Dawe et al ., 2003)
demonstrated that SOM had a significant
control on crop productivity and function-
ing. This was later highlighted by Manlay
et al . (2007). Recently, when reviewing the

Organic matter is considered as vital to the
soil fertility of croplands, and has been pro-
posed as a key soil parameter for the charac-
terization of soil quality, productivity and
ecosystem functioning (Tiessen et al ., 1994).
Moreover, topsoil soil organic matter (SOM)