Alleviating global warming potential by soil carbon sequestration: A multi-level straw incorporation experiment from a maize cropping system in Northeast China

Management practices used on croplands to enhance crop yields and quality can contribute about 10–20% of global greenhouse gases (GHGs: carbon dioxide [CO2], nitrous oxide [N2O], and methane [CH4]). Some of these practices are tillage, cropping systems, N fertilization, organic fertilizer application, cover cropping, fallowing, liming, etc. The impact of these practices on GHGs in radiative forcing in the earth’s atmosphere is quantitatively estimated by calculating net global warming potential (GWP) which accounts for all sources and sinks of CO2 equivalents from farm operations, chemical inputs, soil carbon sequestration, and N2O and CH4 emissions. Net GWP for a crop production system is expressed as kg CO2 eq. ha−1 year.−1 Net GWP can also be expressed in terms of crop yield (kg CO2 eq. kg−1 grain or biomass yield) which is referred to as net greenhouse gas intensity (GHGI) or yield-scaled GWP and is calculated by dividing net GWP by crop yield. This article discusses the literature review of the effects of various management practices on GWP and GHGI from croplands as well as different methods used to calculate net GWP and GHGI. The paper also discusses novel management techniques to mitigate net CO2 emissions from croplands to the atmosphere. This information will be used to address the state of global carbon cycle.

Effects of long-term straw incorporation on the net global warming potential and the net economic benefit in a rice–wheat cropping system in China

A long-term fertilizer experiment investigating cotton-based cropping systems established in 1990 in central Asia was used to quantify the emissions of CO2, CH4 and N2O from April 2012 to April 2013 to better understand greenhouse gas (GHG) emissions and net global warming potential (GWP) in extremely arid croplands. The study involved five treatments: no fertilizer application as a control (CK), balanced fertilizer NPK (NPK), fertilizer NPK plus straw (NPKS), fertilizer NPK plus organic manure (NPKM), and high rates of fertilizer NPK and organic manure (NPKM+). The net ecosystem carbon balance was estimated by the changes in topsoil (0–20 cm) organic carbon (SOC) density over the 22-year period 1990–2012. Manure and fertilizer combination treatments (NPKM and NPKM+) significantly increased CO2 and slightly increased N2O emissions during and outside the cotton growing seasons. Neither NPK nor NPKS treatment increased SOC in spite of relatively low CO2, CH4 and N2O fluxes. Treatments involving manure application showed the lowest net annual GWP and GHG intensity (GHGI). However, overuse of manure and fertilizers (NPKM+) did not significantly increase cotton yield (5.3 t ha−1) but the net annual GWP (−4,535 kg CO2_eqv. ha−1) and GHGI (−0.86 kg CO2_eqv. kg−1 grain yield of cotton) were significantly lower than in NPKM. NPKS and NPK slightly increased the net annual GWP compared with the control plots. Our study shows that a suitable rate of fertilizer NPK plus manure may be the optimum choice to increase soil carbon sequestration, maintain crop yields, and restrict net annual GWP and GHGI to relatively low levels in extremely arid regions.

AimsTo assess 1) the effect of the combination of flooding (winter flooding vs. non-winter flooding; WFL vs NWF) and timing of straw incorporation (early vs late straw incorporation; ESI vs LSI) in the post-harvest of paddy agrosystem, on a year-round global balance of greenhouse gases (GHG) exchanges, i.e. methane (CH4), carbon dioxide (CO2) and nitrous oxide (N2O); 2) the impact on the net ecosystem carbon balance (NECB) and 3) the resulting net global warming potential (GWP).MethodsA field experiment was conducted with fortnightly samplings of main GHG emissions. Effect of the studied factors on GHG emissions was seasonally assessed. The net GWP is estimated from the balance between GHG (CH4 and N2O) and NECB.ResultsNWF-LSI reduced net GWP by 206% compared to conventional post-harvest management (WFL-ESI). NECB was similar in all treatments. Avoiding winter flooding reduced CH4 emissions significantly in the post-harvest and next growing seasons, while delay straw incorporation prevented CH4 and CO2 emissions during post-harvest. None of the treatments increased N2O emission. Environmental implications of post-harvest management options are discussed.ConclusionsPost-harvest management affects net GWP of the paddy rice cultivation by modifying GHG emissions in post-harvest and next growing season without compromise sequestration C budget. The combination of non-winter flooding and late straw incorporation strategies were more effective in reducing both CH4 and CO2 emissions, due to avoiding higher temperatures at the time of the straw incorporation during post-harvest and increasing soil Eh conditions at the following growing season.

Composting and compost application: Trade-off between greenhouse gas emission and soil carbon sequestration in whole rice cropping system

Reduced tillage is a useful practice to increase soil organic carbon (SOC) stock and decrease methane (CH4) emission in a rice paddy. However, the impacts of reduced tillage on the global warming potential (GWP) are generally analyzed for CH4 fluxes only during rice cultivation season. This study was conducted to investigate the effects of tillage on greenhouse gas (GHG) emission including both CH4 and nitrous oxide (N2O) and SOC stock changes were evaluated during the fallow season under two different tillage systems (conventional tillage and reduced tillage practice). The emission rate of GHG emissions was monitored using the closed chamber method. The SOC stock changes were estimated by the net ecosystem C budget (NECB), which is defined as the difference between total organic C input and output. Finally, the net global warming potential (net GWP), which was calculated as CO2 equivalents was compared between the different tillage system in rice paddy during fallow season. The net GWP of tillage and reduced tillage treatment were 4.09 and 4.96 Mg CO2 eq. ha-1, respectively during fallow season. However, the net GWP was not significantly different tillage systems. The decrease of SOC stock as CO2 emission was the most influential part on increasing the net GWP. Our study suggest that regardless of tillage conditions, it is necessary to establish a greenhouse gas reduction strategy focusing on increasing SOC accumulation during the fallow season. However, as this study was conducted for only single fallow season, long-term study is required to estimate the cumulative effects of tillage treatment on GHG emissions during fallow seasons in paddy.Net global warming potential (net GWP) under different tillage systems during fallow season in rice paddy (CT, conventional tillage; RT, reduced tillage).

Minimum tillage of a cover crop lowers net GWP and sequesters soil carbon in a California vineyard

Negative emissions technologies (NETs) are expected to play a significant role in mitigating climate change. However, there are also concerns that a large scale deployment of NETs may cause various environmental impacts due to the use of land, water and energy resources. A number of studies have assessed the environmental performance of various NETs; however, a comprehensive review comparing a range of different NETs is not available in the literature. To address this research gap, this paper compares life cycle assessment (LCA) studies of the following options for which the data were available in the literature: bioenergy with carbon capture and storage (BECCS), biochar incorporation into soil, afforestation and reforestation, soil carbon sequestration, building with biomass, direct air carbon capture and storage (DACCS), enhanced weathering and mineral carbonation. It is evident from this review that these technologies can have net negative life cycle GHG emissions, ranging from −603 kg CO 2 eq./t CO 2 removed for building with biomass to −1173 kg CO 2 eq./t CO 2 removed for biochar incorporation into soil. However, the estimates of GHG removal potentials vary widely among the studies for each technology as well as among the NETs owing to technological differences, methodological choices and differing assumptions. For example, the net global warming potential (GWP) of biochar varies among the reviewed studies between a net positive impact of 1710 to a net negative GWP of 3300 kg CO 2 eq./t CO 2 removed, depending upon the feedstock, pyrolysis technology and the assumptions for credits for co-products and co-benefits. Overall, biochar used as soil amendment has the lowest GWP per tonne of CO 2 removed, followed by soil carbon sequestration, while building with biomass ranks last. The review also reveals that the removal of CO 2 by these technologies could lead to a significant increase in other environmental impacts. Especially, the use of energy in non-bio NETs (DACCS, enhanced weathering and mineral carbonation) leads to relatively high fossil depletion, acidification and human toxicity. These impacts can be reduced if the energy demand of NETs is met by renewables instead of fossil fuels. The paper also identifies several methodological issues and challenges in conducting LCA of NETs and provides recommendations to address them.

Straw-derived biochar regulates soil enzyme activities, reduces greenhouse gas emissions, and enhances carbon accumulation in farmland under mulching

Biodegradable film mulching combined with straw incorporation can significantly reduce global warming potential with higher spring maize yield

Contrasting effects of straw and straw–derived biochar application on net global warming potential in the Loess Plateau of China

Integrated straw-derived biochar utilization to increase net ecosystem carbon budget and economic benefit and reduce the environmental footprint

Effect of tillage and crop (cereal versus legume) on greenhouse gas emissions and Global Warming Potential in a non-irrigated Mediterranean field

Seven upland cropping systems in Central Hokkaido, Japan, were investigated during the growing season in 2003 to evaluate the magnitude of N2O emission, CH4 uptake and soil carbon sequestration, and their net effect on the global warming potential (GWP). N2O and CH4 fluxes were measured from field soils planted with crops and CO2 fluxes were measured from bare soils in attached plots at each site using the closed chamber method. Cumulative N2O emissions ranged from 0.02 g N m−2 to 0.62 g N m−2 for different soil types, which accounted for 0.35–4.44% of the applied fertilizer nitrogen. Cumulative CH4 uptake rates ranged from −0.08 g C m−2 to 0 g C m−2. Soil carbon sequestration, defined as the difference between the net primary production and carbon loss through harvest and soil microbial decomposition, ranged from −410 to −193 g C m−2, indicating that the carbon loss from soils could not be compensated by the carbon input through plant photosynthesis. The net GWP from the investigated cropping systems ranged from 749 to 1790 g CO2 equivalents m−2. CO2 emission contributed to 84–99% of the net GWP and N2O contributed 1–16%.

Straw incorporation has a variety of impacts on greenhouse gas (GHG) emissions. However, few studies have focused on the effects of multi-year straw incorporation. In this study, a field experiment was established to study the effects of straw incorporation and water-saving irrigation on GHG emissions in the cold region of Northeast China. The following four treatments were included: (i) controlled irrigation (CI) with 1-year straw incorporation (C1), (ii) controlled irrigation with 5-year straw incorporation (C5), (iii) flooded irrigation (FI) with 1-year straw incorporation (F1), and (iv) flooded irrigation with 5-year straw incorporation (F5). The fluxes of N2O, CO2, and CH4 were measured by the static chamber–gas chromatography method, and their global warming potential (GWP) and greenhouse gas intensity (GHGI) in units of CO2-equivalent at the 100-year scale were calculated. The results showed that the 5-year straw incorporation reduced N2O emissions but increased CH4 emissions. Compared with C1 and F1, C5 and F5 reduced N2O emissions by 73.1% and 44.9%, respectively, while increasing the CH4 emissions by 101.7 and 195.8%, respectively. Under different irrigation regimes, CI reduced CH4 emissions by 50.4–79.7% while increasing CO2 emissions by 8.2–44.9% compared with FI. The contribution of N2O and CO2 emissions were relatively high at the mature and milk stages, respectively, with a range of 16–54% and 41–52% for the treatments. In contrast, CH4 emissions were mainly manifested at the tillering stage, with a contribution of 36–58% for the treatments. Affected by higher CH4 emissions in FI, the GWP of CI was 1.4–47.6% lower than FI. In addition, the yield of CI was 10.0–11.5% higher than FI, which resulted in a GHGI of 11.5–52.4% lower than FI, with C5 being the lowest. The irrigation regime of CI combined with 5-year straw incorporation was an effective agronomic measure to increase yield and reduce GHG emissions from paddy fields in the cold region of Northeast China.