Organic Carbon Sequestration Potential and the Co-Benefits in China’s Cropland - Principles of Sustainable Soil Management in Agroecosystems - page 507

historical agricultural development. Lal (2002) estimated a total loss of 3.5 Pg since
the agricultural development in China, including about 2 Pg from land desertification
caused by improper land use (Lal 2002). Lindert et al. (1996) reviewed SOC data from
early agricultural literature published before 1960 and reported severe SOC losses
from a wide range of China's ecosystems. Using the DeNitrification-DeComposition
(DNDC) model, Li (2000) addressed a serious and continuing decline of SOC storage
in China's croplands since the 1950s, resulting in a total SOC stock loss of up to 70 Tg
since the 1970s. Wu et al. (2003) conducted a statistical analysis of SOC storage from
the archived data from the second national soil survey for cultivated soil compared
with natural soils and estimated a loss of whole soil SOC stock of China's croplands
at 7 to 8 Pg, primarily due to historical degradation in SOC storage from cultivation of
the native soils. Drastic loss in SOC stock occurred mainly in the north and other arid
and semiarid regions of China. Nevertheless, it has been argued that there have been
large areas and soil and land use associations where changes in SOC stocks were either
minimal or even where increases in SOC storage had occurred, especially in irrigated
areas (Pan et al. 2003). Song et al. (2005b) used data for cultivated and uncultivated
soils from the national soil survey in a comparative analysis and revealed that cultiva-
tion-induced loss of topsoil SOC stock could be up to 14.8 ± 15.1 Mg/ha, giving a total
stock loss of 2 Pg for cultivated topsoil. Song and colleagues also observed that over
60% of this loss occurred in soils of Northeast China, Northwest China, and Southwest
China. Therefore, the significant loss of SOC stock from soils under intensive cultiva-
tion and increased inorganic fertilizer inputs may account for, at least partly, the low
level of SOC in croplands, but also indicates a significant role of CO 2 emission to the
atmosphere from China's historical land use/land cover changes.
18.2.3 c arBon S tock d ynamicS and S equeStration
Between 1980 and 2006
The SOC stock of croplands, among other C reservoirs in the terrestrial ecosystem,
is prone to anthropogenic activities, especially with progressive advances in agri-
cultural technology. China's agriculture experienced consecutive increases in crop
production capacity for ensuring food supply with technology transfer for improv-
ing crop management since the earlier 1980s, and consequently, the SOC followed
an increasing trend in cropland soils. Thus, several studies have reported adverse
impacts of China's intensive agriculture on natural resources and the environment,
including increase in desertification, extension of arid areas, secondary salinization,
N overuse, and water quality deterioration, as well as historical SOC loss. However,
an increase in overall topsoil SOC stock has also been well documented at a county
level in Jiangsu (Zhang et al. 2004b), a village level in Jiangxi (Zhang 2004), and a
regional level in the North China plain and Northeastern China's black soil region
(Xu et al. 2004).
The increase in topsoil SOC stock has been validated by a range of long-term
agroecosystem experiments as well as by modeling. Data from long-term agroeco-
system experiments show topsoil SOC enhancement over the last decades. For exam-
ple, increases in topsoil SOC stocks have been reported with rational fertilization,
mainly via combined use of organic and inorganic fertilizers, over 10 to 20 years