Agricultural intensification has contributed greatly to the sustained food
supply of China's population of 1.3 billion over the 30-year period from 1982
to 2011. Intensification has several and widely recognized negative
environmental impacts including depletion of water resources, pollution of
water bodies, greenhouse gas emissions and soil acidification. However, there
have been few studies over this period on the impacts of intensification on
soil organic carbon (SOC) at the regional level. The present study was
conducted in Huantai County, a typical intensive farming region in northern
China, to analyze the temporal dynamics of SOC influenced by climate and
farming practices. The results indicate that from 1982 to 2011, SOC content
and density in the 0–20 cm layer of the cropland increased from
7.8
Increasing soil organic matter (SOM) storage in arable lands can ensure the
sustained supply of nitrogen (N) and other nutrients to crop growth and
maintain appropriate soil quality such as aeration, permeability,
water-holding capacity and nutrient preserving capacity (Smith et al., 2012).
Globally, accumulation of SOM or soil organic carbon (SOC) stock in arable
lands, which contribute to the mitigation of greenhouse effect and a
concomitant improvement in soil fertility (Matson et al., 1997; Sainju et
al., 2009), may be achieved by a range of improved farming practices. These
practices include adoption of high-yielding crop varieties, balanced
fertilization, crop residue incorporation, no-till (NT) or reduced tillage,
optimal irrigation, high cropping intensity (Matson et al., 1997; Kucharik,
et al., 2001). For instance, agricultural soils in the USA had a carbon sink
capacity of from 1.3 to 21.2 Tg C annually from 1982 to 1997, due to land use, NT,
higher cropping intensity, etc. (Eve et al., 2002; Ogle et al., 2003). The
rate of increase in SOC stock in Canada was 5.7 Tg C yr
Northern China is one of the most important agricultural regions, producing
60–80 % and 35–40 % of nation's wheat (
We collected 3 decades of data of climate, farm management and crop yield from Huantai County to (1) analyze the evolution of SOC at the regional level from 1982 to 2011 and (2) establish the cause–effect relationship between the driving forces and SOC change. The results derived from this study may contribute to improved farm management for the long-term sustainable agricultural development in the intensive farming of northern China and elsewhere.
Huantai County, with an area of 509 km
The soil, climate and farming data were collected between 2011 and 2013 from the
sources as described below:
where where SOC is the soil organic carbon content (g kg
The Kolmogorov–Smirnov test was used in the SPSS Statistics 17.0 package to determine if SOC content followed a normal distribution. Central tendency, dispersion degree and distribution characteristics of SOC data were calculated. Pearson correlation analysis and/or partial correlation analysis were conducted between SOC content and driving factors including mean annual temperature, mean annual precipitation, grain yield, nitrogen fertilizer rate and straw C incorporation. A multivariate regression model was developed to account for the impact of these factors on temporal SOC change in Huantai County.
Evolution of SOC content and density for cropland from 1982 to 2011 in Huantai County. Error bars are shown only for the years which soil survey is undertaken.
Figure 1 presents the dynamic changes of topsoil SOC content and density for
the cropland (winter wheat–summer maize) from 1982 to 2011. The mean
increase in cropland from 1982 to 2011 was from 7.8
An adjustment in the local agricultural sector altered the land use between
1982 and 2011 in Huantai County. The farmland area in 1982 was 35 204 ha,
of which more than 99 % was winter wheat–summer maize cropping
(cropland). Due to the expansion of vegetable production starting in the
1990s, land used for vegetable production increased to about 20 % by the
early 2000s, and has remained constant through 2011 at about 6000 ha. The
average SOC content of vegetable land is not significantly different from
that of cropland (11.0 vs. 11.0 g kg
Correlation analysis between SOC content of cropland and driving factors in Huantai County.
Change of SOC stock for farmland (cropland, vegetable land, farmland converted to construction land) from 1982 to 2011 in Huantai County.
Although cropland area decreased from 35 204 ha in 1982 to 24 343 ha in
2011, the SOC stock of cropland (0–20 cm) increased from 0.75
Among the natural/climate forces which can influence SOC level, mean air
temperature in Huantai County increased within the period of 1982–2011, with
a relationship represented by the regression equation
Correlation and regression analyses were performed between SOC of cropland
and driving factors, i.e., temperature, precipitation, crop (wheat and maize)
yield, N fertilizer rate and C input from crop residues (Table 1). There was
a highly significant correlation (
Regression analysis of driving factors with the years in Huantai.
Partial correlation analysis between SOC content of cropland and driving factors in Huantai County.
A partial correlation analysis was conducted to determine the relationship
between SOC content of cropland and any major driving factor, as the
effect of a set of controlling random variables was removed (Table 2). The data
indicated a highly significant and positive correlation between SOC content
and the C input from crop residues (
The SOC level of farmland was influenced by climate (mainly temperature and precipitation) and farming practices, including crop residue incorporation, N fertilizer use, crop yield, etc. (Khan et al., 2007; Ladha et al., 2011).
A few studies (Khan et al., 2007; Mulvaney et al., 2009) have reported that
even the long-term input of a massive amount of residue C and synthetic N
fertilizer do not sequester SOC; this was not the case with the
intensification of cropland in northern China. A major factor lies in the
concentration of the principal parameter (i.e., SOM) which was significantly
lower in cropland soils of northern China than those of the US Corn Belt (9
vs. 25 g kg
Balanced fertilization should be widely promoted for optimization of the
integrated economic benefits and ecosystem services. It is important to
understand that increasing the input of N fertilizer increased SOC only when
crop residues were returned to the soil. There may have been either no or
only a slight increase in SOC level if the aboveground crop residues were
removed or burnt (Alvarez, 2005); therefore, N fertilization in itself is not a
suitable strategy to increase SOC, particularly considering the overriding
effects of N
Miao et al. (2011) reported the significance of N fertilizer and crop residues incorporation to the maintenance and increase of the SOM. Retention of residues (wheat and maize) in conjunction with the appropriate rate of N fertilization have been properly implemented in northern China where the antecedent levels of SOM are much lower than those in North America and western Europe. Therefore, a reasonable continuation of these practices will continue to accumulate SOM for a long time to come. However, similar trends may not occur under all situations. For example, Khan et al. (2007) explained that after attaining a steady state, it is unlikely that SOC will continue to increase, and may even decline with continuous use of synthetic N because of the enhanced activities of heterotrophic soil microorganisms in using crop-derived residues or SOM. In the context of northern China, therefore, it is likely that the increase in SOC level will continue because of the improved crop productivity and retention of crop residues, but it will eventually attain a new equilibrium. Some other SOC-enhancing practices including application of residue-based animal manure derived from the same land unit contribute further to SOC sequestration. In addition, higher levels of mechanization during the agricultural intensification process may increase the soil BD (about 7 % in our study), and this also contributed to the increase of SOC stock and should not be ignored when quantifying of farmland carbon sequestration.
Topsoil (0–20
Continued.
Agriculture in China has grown rapidly over the 3 decades since 1982, primarily because of the household contract responsibility system and adoption of the reform and open policy by the central government. Further, the intensification process has achieved some economic and environmental benefits (Firbank et al., 2013). In the case of northern China, however, there were also problems with increases in soil compaction and water pollution over the last 3 decades.
Among all agronomic regions, northern China registered the highest rate of
SOC sequestration. In contrast, however, the SOC level has declined in
northeast China since the 1980s (Table 3). Northeast China, one of the few
world regions characterized by the black soil (Phaeozems) and cold climate,
has high antecedent SOC content (
Agricultural intensification in China is an ongoing process, and is progressively evolving over time. For instance, since 2012, maize residues from some cropland have been harvested by Huantai farmers for use as cattle feed and the eventual return of the animal manure to cropland. It is possible that the efficiency of SOM accretion through animal manure is higher than that of returning maize straw (Wilhelm et al., 2007), which may result in yet another period of SOM accretion at the regional level with proper dissemination of this technology (Ladha et al., 2011). Similar to northern China, other important grain production region like the Midwest USA also experienced the stage of SOC accumulation, although the practices (residue management, non- or reduced tillage and crop rotation) are different (Ogle et al., 2003; Jelinski and Kucharik, 2009). Adoption of conservation agriculture (NT or minimum tillage) may be another option for SOC sequestration. However, its applicability and efficiency need to be validated through long-term research.
The study of the impact of agricultural intensification on SOC content and stock was conducted in Huantai County, which is a representative region of northern China. The farmland SOC stock of the whole county increased by more than 50 % over the 3 decades from 1982 to 2011. Among several improved farming practices, the retention of crop residues strongly contributed to the restoration of SOC, but there was no synergistic effect between N fertilization rate and crop yield on increase in SOC. The SOC content decreased with an increase in mean annual temperature. The temporal change in SOC was significantly influenced by the evolution of the practice of retaining crop residues through implementation of local farming policies. The data support the conclusion that agricultural intensification may both increase crop productivity and enhance some ecosystem services, such as SOC sequestration in croplands of northern China. However, current farming practice (e.g., retention of crop residues) may not always linearly increase SOC over time, indicating a strong need for long-term research. Furthermore, there is also need to explore other options such as the application of manure through integration of crop and animal production. Research on the use of animal manure within the region is a priority, because of its multiple benefits for grain production, the economy and ecosystem services such as SOC sequestration.
Fanqiao Meng, Wenliang Wu and Yan Liao designed the experiments and Yan Liao carried them out. Yan Liao and Pete Smith performed the calculations and data analysis. Yan Liao, Fanqiao Meng, Pete Smith and Rattan Lal prepared the manuscript with contributions from all co-authors.
This research was supported by National Natural Science Foundation of China (no. 31370527 and 31261140367) and the National Science and Technology Support Program of China (no. 2012BAD14B01-2). The authors gratefully thank the Huantai Agricultural Station for providing of the Soil Fertility Survey data. We also thank Zheng Liang from China Agricultural University for the soil sampling and analysis in 2011. Thanks are extended to Jessica Bellarby for helpful discussion and suggestions. Edited by: Y. Kuzyakov