Effects of long-term fertilization and residue management on soil organic carbon changes in paddy soils of China: A meta-analysis
Introduction
Soil organic carbon (SOC) in agricultural ecosystems plays a positive role in soil fertility, soil tilth, soil sustainability and crop production (Bauer and Black, 1994, Lal and Kimble, 1997). It is well known that agricultural management can increase or decrease SOC content due to variations in tillage, fertilization, irrigation and other activities (Paustian et al., 1997, Ogle et al., 2005). Consequently, improved management practices should aim to increase SOC accumulation, as these practices affect both world food security and global climate change (Lal, 2004, Lal, 2007).
Increasing evidence indicates that improved management practices can increase agricultural SOC to levels similar to those found in natural lands (Smith et al., 2000, West and Post, 2002, Lal, 2004, Gattinger et al., 2012). The SOC change rate results from the net balance between the rate of SOC input and the rate of mineralization (Post and Kwon, 2000). Carbon inputs to soil are mainly controlled by the biomass productivity of cropping systems, which is a function of the variations in climate, soil conditions, fertilizer inputs and agronomic management. Fertilizer application can enhance crop yield and biomass productivity, which increases the biomass input into the soil from crop residues and roots. Straw return and/or organic manures add carbon directly to soil. Several field experiments have proven that these measures can increase soil carbon and sequester C from the atmosphere (Halvorson et al., 1999, Kapkiyai et al., 1999, Wu et al., 2004, Ogunwole, 2005, Cong et al., 2012). In general, the application of organic fertilizers, especially manure, applied alone or in combination with inorganic fertilizers, increases SOC concentration (Manna et al., 2007, Purakayastha et al., 2008, Gong et al., 2009, Cong et al., 2012).
Paddy soils are a major form of cultivated soil in China. These soils, which account for approximately 25% of the total cultivated land, cover a total area of 30 M ha and are widely distributed across a broad range of temperate, subtropical and tropical climates (Shi et al., 2010, Zhang et al., 2012). Therefore, accurate estimates of the SOC changes in China’s paddy soils are critical for understanding their contribution to agro-ecosystem sustainability and the sequestration of atmospheric CO2. SOC change is a process that is controlled by many factors, including organic C inputs from crop residue or applied organic manure, climatic and soil conditions, and original C levels, and thus has high spatiotemporal heterogeneity. A realistic estimate of the change in SOC at regional and national scales must account for the effects of heterogeneity in soil and climate conditions and spatiotemporal management practices on SOC changes (Yan et al., 2007, Luo et al., 2013). However, there is a significant lack of spatiotemporally explicit quantification of SOC change and its sustainability with improved soil management in the paddy soils of China.
Process-based biogeochemical models, such as DNDC (Li et al., 1994), Century (Parton et al., 1987), RothC (Coleman et al., 1997), CEVSA (Cao et al., 2003) and EPIC (Izaurralde et al., 2006), are useful tools for simulating SOC changes in agricultural soils (Paustian et al., 1992) and provide a means of predicting, monitoring and verifying SOC changes under diverse conditions at a field scale (Bricklemyer et al., 2007). Some attempts have been made to upscale individual site results to quantify potential C sequestration at regional and national scales in China (Li et al., 2003, Tang et al., 2006, Yan et al., 2007, Wang et al., 2011, Xu et al., 2012). However, these process-based models usually require detailed input information, particularly spatially distributed information on agricultural practices and management history, which is typically not available at regional and/or global scales (Luo et al., 2013, Jandl et al., 2014). Hence, there is great uncertainty in simulating SOC changes and upscaling the results from individual sites to a regional scale (Ogle et al., 2006, Ogle et al., 2010, Smith et al., 2010). A meta-analysis is an effective statistical method to quantitatively summarize the results of numerous individual and independent studies and allows general conclusions to be drawn at regional and global scales (Gurevitch and Hedges, 1999, Guo and Gifford, 2002). The effects of agricultural practices on soil carbon changes have been investigated in numerous field experiments. Therefore, we conducted a meta-analysis to integrate the results of previous studies that examined changes in SOC due to fertilization and residue return in paddy fields in China. SOC measurements and auxiliary data were specifically compiled to
- (a)
comprehensively assess the spatiotemporal changes in SOC in paddy soils in China;
- (b)
provide confidence intervals for estimates of soil C change rates;
- (c)
quantitatively estimate the duration of soil C sequestration rates and soil C sequestration potential.
Section snippets
Data sources
We collected data on the changes in soil organic carbon (SOC) contents under different fertilization treatments from all peer-reviewed research papers published before 2013. The SOC contents in the analysis were obtained from the published tables and text of all of the selected research articles, and some data were extracted from published figures using graph digitizing software. Experimental site information, including the experimental periods, cropping systems, fertilization schemes and soil
The mean difference in SOC change rates in the fertilization treatments
There were positive SOC sequestration effects in all fertilization trials (Fig. 2a). The bias-corrected CIs of the mean differences were greater than zero for all treatments, indicating a significant effect on carbon sequestration in the paddy topsoil (Fig. 2a). Specifically, the greatest mean difference in SOC change rates occurred under NPKM treatment, with a rate of 0.401 g kg−1 yr−1, while the N treatment resulted in the lowest rate of 0.046 g kg−1 yr−1 compared with the control (CK). The
Initial SOC content
According to the soil C saturation hypothesis, changes in SOC may be affected by initial C levels (Campbell et al., 1991, Stewart et al., 2007). A greater SOC sequestration potential was observed in soils with a low C content compared with those with a high C content because they were further from their saturation level (Stewart et al., 2007, Stewart et al., 2008). A linear equation or a logarithmic function has been used to describe the relationship between SOC changes and their initial C
Conclusion
Our meta-analysis indicated that fertilizer application and straw return can significantly increase the SOC content compared with a control (CK) without fertilization. The combination of manure and inorganic fertilizers (NPKM) is the most promising strategy to maximize SOC levels. In contrast, the lowest increase in SOC levels were observed in response to mineral nitrogen (N) applied alone. The rates of the SOC change decreased with time and experiment duration. The duration of SOC
Acknowledgements
We are grateful to the authors who shared additional information on studies chosen for our meta-analysis. We acknowledge the support for this research from the Natural Science Foundation of China (41471177), the Strategic Priority Research Program of Chinese Academy of Sciences–Climate Change: Carbon Budget and Relevant Issues (XDA05050509) and the National Basic Research Program of China (973 Program) (2010CB950702).
References (84)
- et al.
Influence of fertilizer and straw baling on soil organic matter in a thin Black Chernozem in western Canada
Soil Biol. Biochem.
(1991) - et al.
Chronosequential changes of selected pedogenic properties in paddy soils as compared with non-paddy soils
Geoderma
(2009) - et al.
Simulating trends in soil organic carbon in long-term experiments using RothC-26.3
Geoderma
(1997) - et al.
Carbon sequestration in the agricultural soils of Europe
Geoderma
(2004) - et al.
Influence of tillage and plant residue management on respiration of a Florida Everglades Histosol
Soil Tillage Res.
(2007) - et al.
Simulating soil C dynamics with EPIC: model description and testing against long-term data
Ecol. Model.
(2006) - et al.
Current status, uncertainty and future needs in soil organic carbon monitoring
Sci. Total Environ.
(2014) - et al.
Effects of forest management on soil C and N storage: meta analysis
For. Ecol. Manage.
(2001) - et al.
Controls over soil microbial biomass responses to carbon amendments in agricultural systems: a meta-analysis
Agric. Ecosyst. Environ.
(2011) - et al.
Soil organic matter and nutrient dynamics in a Kenyan nitisol under long-term fertilizer and organic input management
Soil Biol. Biochem.
(1999)