Chapter One
Management-Induced Changes to Soil Organic Carbon in China
A Meta-analysis
Xin Zhao
*, Ran Zhang
*, Jian-Fu Xue
*, Chao Pu
*, Xiang-Qian Zhang
*, Sheng-Li Liu
*, Fu Chen
*, Rattan Lal
§ and Hai-Lin Zhang
*,
1 *College of Agronomy and Biotechnology, China Agricultural University, Key Laboratory of Farming System, Ministry of Agriculture, Beijing, China §Carbon Management and Sequestration Center, School of Environment and Natural Resources, The Ohio State University, Columbus, OH, USA 1 Corresponding author: E-mail:
hailin@cau.edu.cn Abstract
Soil carbon (C) sequestration is an environmentally friendly and efficient strategy to offset emissions of greenhouse gases and mitigate climate change. However, inappropriate farming practices can deplete soil organic carbon (SOC) stock and degrade soil quality. Thus, we conducted a meta-analysis to assess and identify the effects of improved farming practices on SOC sequestration in China by compiling a data set of 83 studies. The results indicated that SOC concentration and stocks at 0–30cm depth significantly increased by 1.00±0.26gkg-1 and 0.97±0.24Mgha-1 when plow tillage with residue removal was converted to no-till with residue retention (NT); 1.11±0.21gkg-1 and 2.09±0.46Mgha-1 when no fertilization was changed to chemical fertilization (CF); and 1.99±0.62gkg-1 and 3.09±0.99Mgha-1 when CF was changed to manure application (MF) (P<0.05), respectively. However, increases in SOC were primarily observed in the surface layer and decreased with soil depth. Therefore, the adoption of NT and MF in conjunction with CF is an effective strategy to enhance SOC stock in the surface layer. Further, in single-crop farming regions, the effects are more significant at 0–10cm depth; and the new equilibrium can occur within 11–20years after the adoption of NT. In double-crop farming regions, conversion to MF enhanced the SOC at 0–20cm depth over 16years. Additional research is warranted to credibly assess the rates of residue and manure input, soil “C saturation,” and soil type on the potential SOC sink capacity in China's croplands.
Keywords
Climate-smart agriculture; Farm practices; Meta-analysis; Soil organic carbon; Soil organic carbon stock
List of Abbreviations
BD
Soil bulk density
C
Carbon
CA
Conservation agriculture
CF
Chemical fertilization application
CI
Confidence interval
F0
No fertilization
MAP
Mean annual precipitation
MAT
Mean annual temperature
MD
Mean difference
MF
Manure application
NT
No-till with residue retained
NT0
No-till with residue removal
PT0
Plow tillage with residue removal
R0
Residue removal
RR
Residue retained
SOC
Soil organic carbon
SOM
Soil organic matter
1. Introduction
The Fifth Intergovernmental Panel on Climate Change (IPCC) reported that the global mean surface temperature has significantly increased since the late nineteenth century: the global combined land and ocean temperature increased by 0.89°C (0.69–1.08°C) between 1901 and 2012 (
IPCC, 2013). Climate change is attributed to anthropogenic emissions of greenhouse gases (GHGs), which include CO2, CH4, and N2O (
Lal, 2004a). The use of fossil fuels and land use conversion have released 545 (460–630) Pg (Pg=petagram=1015g=1giga ton) of carbon (C) to the atmosphere, leading to an increase in atmospheric CO2 concentration from 275–281ppmv in 1750 to 390.5ppm in 2011 (
IPCC, 2013) and 400ppmv in 2013 (
WMO, 2014). Thus, identifying strategies of reducing GHGs emissions and mitigating climate change are global issues (
Paustian et al., 2000;
Lal, 2004c,
2007;
Lal et al., 2007). Soil C pool is the third principal global C stock containing 1220–1550Pg to 1m and 2376–2450Pg to 2m depth as soil organic carbon (SOC) and 695–748Pg to 1m depth as inorganic C (
Lal et al., 1995;
Batjes, 1996). The potential of SOC sequestration is estimated to be 0.4–1.2PgCyr
-1 throughout the world's croplands (
Lal, 2004c). Thus, enhancing SOC sequestration is important to partially offsetting anthropogenic emissions and mitigating climate change. In addition, SOC is a key soil property and an important determinant of soil quality (
Reeves, 1997;
Sá and Lal, 2009;
Brandão et al., 2011). However, conversion of natural to agricultural ecosystems may deplete the SOC pool by as much as 60% in temperate regions and 75% or more in tropical regions, degrading soil quality and biomass productivity, exacerbating risks of food insecurity, and aggravating climate change (
Lal, 2004c,
2010;
Lal et al., 2007). Thus, promoting farming practices which can restore SOC stock is important to mitigating climate change, improving soil quality, and advancing food security (
Lal, 2007).
The SOC pool is affected by a wide range of agricultural management practices including tillage (
West and Post, 2002;
Ussiri and Lal, 2009;
Dalal et al., 2011;
Zhang et al., 2014), residue management (
Lu et al., 2009;
Ding et al., 2014;
Liu et al., 2014b), fertilization (
Lu et al., 2009;
Ding et al., 2014), manure application (MF) (
Ding et al., 2014;
Maillard and Angers, 2014), water management and soil drainage (
Abid and Lal, 2008), etc. Thus, a wide range of C-smart practices have been adopted and popularized to replace traditional management practices. Conservation agriculture (CA) is widely practiced and typically leads to minimal soil disturbance (e.g., no-till, NT) and residue retention on the surface as mulch. In addition to enhancing the SOC pool, CA has numerous benefits of relevance to the environment and crop production (
Delgado et al., 2013;
Zhang et al., 2014). Thus, conversion of conventional tillage (e.g., plow tillage) to NT can result in redistribution of SOC within the soil profile (
Powlson et al., 2014) and in soil-specific situations also enhance the SOC pool (
West and Post, 2002;
Zhang et al., 2014), particularly in surface soil (
West and Post, 2002;
Lu et al., 2009;
Zhang et al., 2013b). Conversion to CA also enhances soil quality, increases aggregation, and improves aeration by enriching the surface SOC (
Doran and Parkin, 1994;
Franzluebbers et al., 2007). Agronomic yield in degraded soils can be increased by restoring the SOC pool (
Lal, 2004c). Adoption of recommended management practices (RMPs) and integrated nutrient management are some of the strategies that can be used to restore SOC stock in depleted and degraded soils. However, the rate of SOC restoration is affected by numerous factors including climate (rainfall, temperature, evaporation, and seasonal distribution), soil texture and structure, farming system, and specific RMPs of soil and crop management (
Lal, 2004c;
Johnston et al., 2009). SOC sequestration is to enhance the SOC stock compared to the pretreatment status due to soil humus through land unit plants, plant residues, and other organic solids that originate from the atmospheric CO2 pool (
Olson, 2013;
Olson et al., 2014). Because of the complexity of SOC sequestration, the amounts of SOC sequestration attained under different farming practices are not clear and have numerous uncertainties. For example, the impact of NT on SOC concentration and pool follows different trends in the long- or short-terms due to experimental...
