Organic Carbon Sequestration Potential and the Co-Benefits in China’s Cropland - Principles of Sustainable Soil Management in Agroecosystems - page 510

the loss of biophysical protection of SOC in the paddy. Land ownership and manage-
ment system changes can also impact on cropland SOC dynamics. Fragmentation of
land holdings, as affected by household ownership, has prevailed for a long time in
China (Tan et al. 2006) and has caused adverse effects on land quality, resource effi-
ciency, and profitability of agriculture (Tan et al. 2008; Rahman and Rahman 2009).
The potential impact of the land fragmentation on SOC had received much attention
elsewhere but not in China (De Costa et al. 2006). A pilot study of soil quality and
household farming was conducted in a rural area of Jiangxi Province where the local
people had been living on the land (Feng et al. 2011). They concluded that the topsoil
SOC stock varied widely from 1.7 to 25.2 g/kg, depending on the size of the total
cropland area and the land tenure status. The amount of SOC in plots of <0.1 ha was
significantly lower (by 20%) than in those of >0.1 ha, and the owned croplands had
a higher SOC level by almost 100% on average than those leased or contracted out.
Therefore, improving land tenure and land management systems could play a key
instrumental role in enhancing SOC sequestration in China's croplands.
Therefore, the SOC sequestration in cropland soils of China could be accounted
for mostly by the increasing amount of straw or residues being returned, and these
increased crop inputs have been affected by fertilizer application as well as enhanced
humification with increased N status. However, a low rate of SOC sequestration and
even loss of SOC in some cropland soils could occur in some regions of China (Figure
18.6). While SOC sequestration could be prominent in East, North, and Northwest
China, large losses have happened in Northeast and also in Southwest China. The
region of Southwest China had been recognized as an ecotone vulnerable to climate
changes due to the shallow soils on limestone terrains and a widespread problem of

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25

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15

10

5

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Northeast North Northwest East Central SouthSouthwest

FIGURE 18.6 Mean background value and the value after t years of monitoring of crop-
lands from major crop production regions of China. (From Xu, X.W., Regional Distribution
and Variation of SOC Storage in Agricultural Soils at Different Scales (in Chinese), Nanjing:
Ph.D. Dissertation of Nanjing Agriculture University, 2009.)