Increased Soil Organic Carbon Storage Research Articles

Green manure removal with reduced nitrogen improves saline-alkali soil organic carbon storage in a wheat-green manure cropping system

The incorporation of green manure into cropping systems is a potential strategy for sequestering soil carbon (C), especially in saline-alkali soil. Yet, there are still unknown about the substitution impacts of green manure on nitrogen (N) fertilizer in wheat-green manure multiple cropping system. Herein, a five-year field experiment was performed to determine the impact of three levels of N fertilizer inputs [i.e., N fertilizer reduced by 0 % (100N), 10 % (90 N), and 20 % (80 N)] with aboveground biomass of green manure removal (0GM) and return (100GM) on soil organic carbon (SOC) storage and its primary determinants. The results demonstrated that no significant interaction on SOC storage was detected between green manure and N fertilizer management. 80 N enhanced SOC storage in bulk soil by 7.4 and 13.2 % in 0–20 cm soil depth relative to 100 N and 90 N (p < 0.05). Regardless of N fertilizer levels, compared with 100GM, 0GM increased SOC storage in bulk soil by 14.2–34.6 % in 0–40 cm soil depth (p < 0.05). This was explained by an increase in soil macro-aggregates (>2 and 0.25–2 mm) proportion contributing to SOC physical protection. Meanwhile, the improvement of SOC storage under 0GM was due to the decrease of soil C- and N-acquisition enzyme activities, and microbial resource limitation. Alternatively, the variation partitioning analyses (VPA) results further suggested that C- and N-acquisition enzyme activities, as well as microbial resource limitation were the most important factors for SOC storage. The findings highlighted those biological factors played a dominant role in SOC accumulation compared to physical factors. The aboveground biomass of green manure removal with N fertilizer reduced by 20 % is a viable option to enhance SOC storage in a wheat-green manure multiple cropping system.

The influence of grazing intensity on soil organic carbon storage in grassland of China: A meta-analysis

Grazing can potentially affect grassland soil carbon storage through selective feeding, trampling and fecal excretion of livestock. The numerous case studies and a few meta-analyses have focused on grazing-induced changes in soil organic carbon (SOC) storage, but the effects of grazing on SOC in major grassland types of China are not clear. In this study, we performed a comprehensive meta-analysis to identify the impact of grazing on soil carbon in China. We found that the key factors affecting the SOC content of grazing grasslands is grazing intensity. Heavy grazing (HG) significantly decreased the SOC content by 7.5 % in major grassland types of China (95 % confidence interval (CI), −11.43 % to −3.57 %, P < 0.001). The SOC content in temperate desert steppes (7.22 %), temperate meadow-steppes (10.89 %) under heavy grazing (HG) showed significantly (P < 0.05) decreased. HG resulted in significant (P < 0.01) decreases in SOC content (6.91 %) of Kastanoze. Our study highlighted that formulating rational grazing strategies according to grassland and soil types was the key to increasing SOC storage and sequestration under climate change and increased human pressure.

Microbial-driven mechanisms for the effects of heavy metals on soil organic carbon storage: A global analysis

Heavy metal (HM) enrichment is closely related to soil organic carbon (SOC) pools in terrestrial ecosystems, which are deeply intertwined with soil microbial processes. However, the influence of HMs on SOC remains contentious in terms of magnitude and direction. A global analysis of 155 publications was conducted to integrate the synergistic responses of SOC and microorganisms to HM enrichment. A significant increase of 13.6 % in SOC content was observed in soils exposed to HMs. The response of SOC to HMs primarily depends on soil properties and habitat conditions, particularly the initial SOC content, mean annual precipitation (MAP), initial soil pH, and mean annual temperature (MAT). The presence of HMs resulted in significant decreases in the activities of key soil enzymes, including 31.9 % for soil dehydrogenase, 24.8 % for β-glucosidase, 35.8 % for invertase, and 24.3 % for cellulose. HMs also exerted inhibitory effects on microbial biomass carbon (MBC) (26.6 %), microbial respiration (MR) (19.7 %), and the bacterial Shannon index (3.13 %) but elevated the microbial metabolic quotient (qCO2) (20.6 %). The HM enrichment-induced changes in SOC exhibited positive correlations with the response of MBC (r = 0.70, p < 0.01) and qCO2 (r = 0.50, p < 0.01), while it was negatively associated with β-glucosidase activity (r = 0.72, p < 0.01) and MR (r = 0.39, p < 0.01). These findings suggest that the increase in SOC storage is mainly attributable to the inhibition of soil enzymes and microorganisms under HM enrichment. Overall, this meta-analysis highlights the habitat-dependent responses of SOC to HM enrichment and provides a comprehensive evaluation of soil carbon dynamics in an HM-rich environment.

Maximizing soil organic carbon stocks through optimal ploughing and renewal strategies in (Ley) grassland

Grassland management effects on soil organic carbon storage under future climate are unknown. Here we examine the impact of ley grassland durations in crop rotations on soil organic carbon in temperate climate from 2005 to 2100, considering two IPCC scenarios, RCP4.5 and RCP8.5, with and without atmospheric CO2 enhancements. We used the DailyDayCent model and a long-term experiment to show that ley grasslands increase soil organic carbon storage by approximately 10 Mg ha−1 over 96 years compared with continuous cropping. Surprisingly, extending ley duration from 3 to 6 years does not enhance soil organic carbon. Furthermore, in comparison with non-renewed grasslands, those renewed every three years demonstrated a notable increase in soil organic carbon storage, by 0.3 Mg ha−1 yr−1. We concluded that management of ploughing and renewal intervals is crucial for maximizing soil organic carbon stocks, through balancing biomass carbon inputs during regrowth and carbon losses through soil respiration.

Combined Effect of Freeze–Thaw Cycles and Biochar Addition on Soil Nitrogen Leaching Characteristics in Seasonally Frozen Farmland in Northeast China

Global climate warming and increased climate variability may increase the number of annual freeze–thaw cycles (FTCs) in temperate zones. The occurrence of more frequent FTCs is predicted to influence soil carbon and nitrogen cycles and increase nitrogen leaching. Biochar has the potential to increase soil organic carbon storage and decrease nitrogen leaching. This study aims to investigate the impact of freeze–thaw cycles (FTCs) on soil nitrogen leaching in temperate zones, considering the potential exacerbation of FTCs due to global climate warming and increased climate variability. This study focuses on how biochar, a carbon-rich material produced from biomass, might mitigate nitrogen leaching by influencing soil characteristics. This study explores the interactions between different laboratory-simulated FTC frequencies (ranging from 0 to 12 cycles) and various biochar addition ratios (0%, 2%, 4%, and 6% w/w) on soil nitrogen leaching based on a total of 60 soil columns. Pearson correlations between the soil quality indicators and nitrogen leaching characteristics were detected, and partial least squares path modeling (PLS-PM) was used to assess the effects of the FTCs, biochar addition ratios, and soil quality indicators on the nitrogen leaching content. The results showed that the amount of leached soil NH4+-N and NO3−-N reached 0.129–1.726 mg and 2.90–7.90 mg, respectively. NH4+-N and NO3−-N first increased and then decreased under the FTCs, with the highest values being observed after the 6th FTC. As the biochar addition ratio increased, the NH4+-N and NO3−-N contents decreased. Correlation analysis showed that the nitrogen leaching content was significantly related to the soil pH, soil organic matter (SOM), NH4+-N content, and microbial biomass carbon content (MBC) (p &lt; 0.01). The results of the conceptual path model revealed that nitrogen leaching characteristics were significantly affected by the pH, SOM, soil nitrogen content, and biochar addition ratio. Our results suggest that biochar addition can help reduce nitrogen leaching in farmland soil in areas with black soil and seasonal freeze–thaw cycles.

Including land management in a European carbon model with lateral transfer to the oceans

The use of cover crops (CCs) is a promising cropland management practice with multiple benefits, notably in reducing soil erosion and increasing soil organic carbon (SOC) storage. However, the current ability to represent these factors in land surface models remains limited to small scales or simplified and lumped approaches due to the lack of a sediment-carbon erosion displacement scheme. This precludes a thorough understanding of the consequences of introducing a CC into agricultural systems. In this work, this problem was addressed in two steps with the spatially distributed CE-DYNAM model. First, the historical effect of soil erosion, transport, and deposition on the soil carbon budget at a continental scale in Europe was characterized since the early industrial era, using reconstructed climate and land use forcings. Then, the impact of two distinct policy-oriented scenarios for the introduction of CCs were evaluated, covering the European cropping systems where surface erosion rates or nitrate susceptibility are critical. The evaluation focused on the increase in SOC storage and the export of particulate organic carbon (POC) to the oceans, compiling a continental-scale carbon budget. The results indicated that Europe exported 1.95 TgC/year of POC to the oceans in the last decade, and that CCs can contribute to reducing this amount while increasing SOC storage. Compared to the simulation without CCs, the additional rate of SOC storage induced by CCs peaked after 10 years of their adoption, followed by a decrease, and the cumulative POC export reduction stabilized after around 13 years. The findings indicate that the impacts of CCs on SOC and reduced POC export are persistent regardless of their spatial allocation adopted in the scenarios. Together, the results highlight the importance of taking the temporal aspect of CC adoption into account and indicate that CCs alone are not sufficient to meet the targets of the 4‰ initiative. Despite some known model limitations, which include the lack of feedback of erosion on the net primary productivity and the representation of carbon fluxes with an emulator, the current work constitutes the first approach to successfully couple a distributed routing scheme of eroded carbon to a land carbon model emulator at a reasonably high resolution and continental scale. Short abstractA spatially distributed model coupling erosion, transport, and deposition to the carbon cycle was developed. Then, it was used to simulate the impact of cover crops on both erosion and carbon, to show that cover crops can simultaneously increase organic carbon storage and reduce particulate organic carbon export to the oceans. The results seemed persistent regardless of the spatial distribution of cover crops.

Vegetation succession accelerated the accumulation of soil organic carbon on road-cut slopes by changing the structure of the bacterial community

More emphasis on the soil carbon sequestration of restored rock-cut slopes will be beneficial for reducing carbon emissions from the transportation sector. However, the changes in soil carbon storage with vegetation succession are unclear. We selected two different highways where the cut slopes had been restored for 3 and 10–20 years in Guangdong Province, China, as the study plots. By examining the two restored slopes at different recovery times, we analyzed the differences in soil organic carbon, soil physicochemical properties and the diversity of the soil microbial communities of road-cut slopes with vegetation succession. The soil organic carbon of restored slopes increased significantly with vegetation succession. Moreover, vegetation diversity increased soil organic carbon storage by reducing the microbial activity of Proteobacteria. Additionally, the results indicated that pH remained a key factor in controlling microbial activity and that the effect of soil moisture was site specific. Additionally, our study highlights the importance of investigating the microbial community, pH, and vegetation diversity for a more complete understanding of the mechanisms that regulate soil organic carbon dynamics in restored slope ecosystems. Understanding the multivariate processes controlling soil organic carbon dynamics should be an important goal of future soil organic carbon research for restoring ecosystems on bare slopes.

Short‐term responses of soil organic carbon and chemical composition of particle‐associated organic carbon to anaerobic soil disinfestation in degraded greenhouse soils

AbstractAnaerobic soil disinfestation (ASD) is a short‐term practice to conquer soil degradation, yet its effects on soil organic carbon (SOC) and its composition remain unclear. A field experiment was conducted in degraded greenhouse soils (C3) that were previously used for production of vegetable (VP) and flower (FP), with three treatments (i.e., control, ST [maize straw addition [C4]] and ASD [both ST and water flooding]) for 21 days. Results indicated that the control soil lost 1.3 Mg C ha−1 in VP and 0.94 Mg C ha−1 in FP, while ST increased SOC storage by over 1.0 Mg C ha−1 in both VP and FP. The ASD increased SOC storage by over 2.0 Mg C ha−1 by forming new SOC and decreasing old SOC loss. Additionally, ASD increased OC concentration in particulate size fractions, particularly in particulate organic matter (POM) with lower basal respiration, and higher hydrophobicity as indicated by an increased ratio of C–H/C=O from POM observed by FTIR. The SEM‐EDS found an enhanced C signal in particle size fractions, especially in POM. Overlap of C, O, Si, Ca, and Fe in mineral‐associated organic matter upon ASD indicated the possible crosslinking between intra‐OC and minerals containing O, Si, Ca, and Fe. The ASD also controlled soil salinization and the pathogen Fusarium oxysporum, resulting in increased tomato yields in both VP and FP. Overall, apart from increasing tomato yields, ASD can enhance SOC storage by increasing OC in particle size fractions within a short term.

Organic amendment effects on cropland soil organic carbon and its implications: A global synthesis

Increasing soil organic carbon (SOC) content can promote soil health and crop yield. Organic amendment application is a common practice to accelerate soil carbon sequestration in cropland. The effects of different organic amendments (e.g., compost, slurry) on SOC are uncertain. Previous studies have investigated SOC response to environmental factors but not well addressed the effect of organic amendment characteristics (e.g., source, liquid/solid form, pH). Depending on 1,972 comparisons from 424 articles, we undertook a meta-analysis approach to explore organic amendment effects on SOC content and the related influence factors. The results show that organic amendment addition increased SOC by an average of 26.9% (or 5.1 Mg C ha−1). Specifically, organic amendments can enhance SOC over the long term (>20 years) or within 1.0 m depth. Organic-residue inputs increased more SOC in regions with an arid climate, alkaline soils, or no-mineral nitrogen application soils than the humid climate regions, acidic soils, and nitrogen application soils, respectively. Sewage sludge and municipal solid waste as organic amendments led to high SOC. The organic amendments' pH and liquid/solid form caused significant differences in SOC accumulation. Amendments with a relatively low carbon content or rich nitrogen content have great potential to increase SOC storage. Our results illustrate the importance of amendment characteristics when estimating the potential of organic amendment addition to soil carbon accumulation. This study highlights that amendment application might be a sustainable strategy to increase soil carbon storage while promoting organic waste utilization.

Straw returning combined with controlled-release nitrogen fertilizer affected organic carbon storage and crop yield by changing humic acid composition and aggregate distribution

Soil organic carbon (SOC) sequestration effectively reduces global CO2 emissions while ensuring crop production and sustainable agricultural development. Evaluating the effects of straw returning combined with controlled-release nitrogen (N) fertilizer on soil organic carbon (SOC) sequestration is necessary. We conducted a long-term (2013–2018) insitu field trial with six treatments: straw combined with no N and two N fertilizer types [no N fertilizer (CKS), conventional N fertilizer (BBFS) and controlled-release N fertilizer (CRFS)] and their corresponding no N and two N fertilizer treatments (CK, BBF, and CRF), each in three replicates. Overall, straw returning combined with N fertilizer (BBFS and CRFS) improves carbon storage and crop yield by changing aggregate distribution, with the effect of CRFS being more substantial. We further found CRFS treatment significantly increased SOC storage in small macro-aggregates (0.25–2 mm) by 9.2% and 28.4%, respectively, compared to BBFS and CKS treatments, which is mainly due to CRFS treatment increasing the proportion of small macro-aggregates (0.25–2 mm) by 8.1% and 20.1%, respectively, in contrast with BBFS and CKS treatments. Compared to BBFS and CKS treatments, CRFS treatment increased the fluorescence intensity of hydrophobic compounds in humic acid (HA) by 45.0% and 107.6%, respectively. Similarly, in small macro-aggregates (0.2–2.5 mm), CRFS treatment significantly increased the fluorescence intensity of hydrophobic compounds in HA. Lastly, structural equation modeling showed that straw returning treatments promote aggregate formation and carbon sequestration by increasing the fluorescence intensity of hydrophobic compounds in HA, ultimately increasing crop yield. Therefore, CRFS treatment is theoretically an effective method to promote SOC storage and increase crop yield and is a viable practice for sustainable agriculture.

Rice husk and husk biochar soil amendments store soil carbon while water management controls dissolved organic matter chemistry in well-weathered soil

Rice agriculture feeds over half the world's population, and paddy soils impact the carbon cycle through soil organic carbon (SOC) preservation and production of carbon dioxide (CO2) and methane (CH4), which are greenhouse gases (GHG). Rice husk is a nutrient-rich, underutilized byproduct of rice milling that is sometimes pyrolyzed or combusted. It is unresolved how the incorporation of these residues affects C dynamics in paddy soil. In this study, we sought to determine how untreated (Husk), low-temperature pyrolyzed (Biochar), and combusted (CharSil) husk amendments affect SOC levels, GHG emissions, and dissolved organic matter (DOM) chemistry. We amended Ultisol paddy mesocosms and collected SOC and GHG data for three years of rice grown under alternate wetting and drying (AWD) conditions. We also performed a greenhouse pot study that included water management treatments of nonflooded, AWD, and flooded. Husk, Biochar, and CharSil amendments and flooding generally increased SOC storage and CH4 emissions, while nonflooded conditions increased N2O emissions and nonflooded and CharSil treatments increased CO2 emissions. All amendments stored ∼0.15 kg C m−2 y−1 more SOC than CH4 emissions (as CO2 equivalents), but the combustion of husk to produce CharSil resulted in the net release of CO2 which negates any SOC storage. UV–visible absorption/fluorescence spectroscopy from the pot study suggests that nonflooded treatment decreased DOM aromaticity and molecular size. Our data show that flooding and amendment of Husk and Biochar maximized C storage in the highly weathered rice paddy soil under study despite Husk increasing CH4 emissions. Water management affected dissolved organic matter chemistry more strongly than amendments, but this requires further investigation. Return of rice husk that is untreated or pyrolyzed at low temperature shows promise to close nutrient loops and preserve SOC in rice paddy soils.

Increasing tree productivity does not translate into greater soil organic carbon storage

Increasing soil organic carbon (SOC) storage is one of the promising solutions to mitigate climate change. Fast-growing trees are a potential tool in this context as they rapidly accumulate C in their biomass and could transfer more organic matter (OM) into the soil. However, the relationship between aboveground productivity and SOC storage remains poorly understood. Five clones with different growth rates were selected from a 14-year-old hybrid poplar plantation located in New Liskeard, ON, Canada. We collected soil cores at 87.5 and 175.0 cm distance from the stem and at 0–20, 20–40 and 40–60 cm soil depth for soil C concentration analysis. The most productive clone DN2 (Populus deltoides × P. nigra) stored less SOC (83 Mg ha−1) between 0 and 60 cm depth than the mid-productive clones 1079 (Populus × jackii (P. balsamifera × P. deltoides)) and 915005 (P. maximowiczii × P. balsamifera) (95 and 96 Mg ha−1 respectively), while the least productive clone 747210 (P. balsamifera × P. trichocarpa) also had a lower SOC stock (85 Mg ha−1) compared to the other clones, but not significantly. There was no relationship between aboveground productivity and SOC stocks and total SOC stocks increased by 6 % when the sampling distance was closer to the tree stems. The difference in SOC stocks between clones was mostly observed at the 20–40 cm depth suggesting the significant effect of roots on SOC storage. Soil C/N ratios were significantly different between clones at 0–20 and 20–40 cm depths suggesting differences in OM decomposition rates between clones. There could be a trade-off between aboveground productivity and litter decomposition rate to increase SOC storage.

Effects of biochar addition on greenhouse gas emissions during freeze–thaw cycles in a black soil region, Northeast China

AbstractAs global warming intensifies, the soil environment in middle to high latitudes will undergo more extensive and frequent freeze–thaw cycles (FTCs), which will significantly affect the carbon and nitrogen cycles of soil ecosystems and aggravate greenhouse gas (GHG) emissions. Biochar can increase soil organic carbon storage and mitigate climate change. To effectively control GHG emissions, soil supplemented with biochar at different application rates (0%, 2%, 4% and 6% [w/w]) under different numbers of FTCs (0, 3, 6, 9, and 12) was selected as the research object. The soil GHG emission characteristics in different experimental treatments and their relationships with soil physical and chemical properties were determined. Our results showed that N2O and CO2 emissions were promoted during FTCs, with values of 3.13–50.37 and 16.22–135.50 μg m−2 h−1, respectively. The order of N2O and CO2 emissions with respect to biochar application rate was as follows: 2% &gt; 0% &gt; 4% &gt; 6%. CH4 emissions were negative during FTCs, varying from −1.62 to −10.59 μg m−2 h−1, and negative CH4 emissions were promoted by biochar. Correlation analysis showed that N2O, CO2 and CH4 emissions were significantly correlated with pH, soil moisture and soil organic matter (SOM), total nitrogen (TN) and –N contents (p &lt; .01). The conceptual path model demonstrated that GHG emissions were significantly influenced by FTCs, moisture, SOM and biochar application rate. Our results indicate that the effects of FTCs on GHG emissions were greater than those of biochar application. Biochar application rates of 4% or 6% should be considered in the future to reduce soil GHG emissions in the black soil region of Northeast China. Our results can help provide a theoretical basis and effective strategy to reduce soil GHG emissions during FTCs in seasonally frozen regions.

Changing plant species composition and richness benefit soil carbon sequestration under climate warming

Abstract Anthropogenic warming and land‐use change are expected to accelerate global soil organic carbon (SOC) losses and change plant species composition and richness. However, how changes in plant composition and species richness mediate SOC responses to climate warming and land‐use change remains poorly understood. Using data from a 7‐year warming and clipping field experiment in an alpine meadow on the Qinghai–Tibetan Plateau, we examined the direct effects of warming and clipping on SOC storage versus their indirect effects mediated by plant functional type and species richness. We found that warming significantly increased SOC storage by 8.1% and clipping decreased it by 6.4%, which was closely correlated with the corresponding response of below‐ground net primary productivity (BNPP). We also found a negative correlation between SOC storage and species richness, which was ascribed to the increased BNPP via enhancing the dominance of grasses and decreasing species richness under warming. The lower SOC storage under clipping was caused by the clipping‐induced decrease in BNPP via weakening the dominance of grasses and increasing species richness. Our findings highlight that the SOC storage in this alpine meadow under climate warming and clipping was primarily governed by BNPP changes, which was mediated by changes in the dominance of grasses and species richness. Overall, our study demonstrates that shifting to the dominance of grasses and changing species richness would benefit soil C sequestration under climate warming, but this positive effect would be dampened by grazing or hay harvest. Read the free Plain Language Summary for this article on the Journal blog.

Catchment vegetation and erosion controlled soil carbon cycling in south-eastern Australia during the last two glacial-interglacial cycles

Vegetation structure in vast semi-arid to temperate continental land masses, such as Australia, plays a considerable role in global terrestrial carbon sequestration. However, whether soil carbon from these regions is a net atmospheric carbon source or sink remains contentious, introducing large uncertainties on long-term storage of vegetation-sequestered carbon dioxide. We investigate the interplay between catchment erosion quantified using uranium isotopes, vegetation (pollen), catchment carbon cycling, wetland response (diatoms), and lake carbon accumulation on glacial-interglacial timescales in south-eastern Australia. The analyses are applied to sediments from Lake Couridjah, in the Sydney Basin during the last (133.5 ka to 107.6 ka) and current (17.8 cal ka BP to present day) glacial-interglacial transitions. Robust phase-relationships between catchment erosion, vegetation composition and carbon cycling during both glacial-interglacial periods were revealed by statistical analyses. Vegetation structure had a direct control on catchment erosion, and, thus, on soil organic carbon (SOC) erosion in the catchment. Overall wetter and warmer peak interglacial conditions promoted the expansion of a canopy and mid-storey vegetation cover reducing catchment erosion, while simultaneously increasing SOC storage, catchment and lake primary productivity, and lake carbon storage. The results suggest increased terrestrial carbon sequestration in temperate Australian landscapes in warmer and wetter climates. • Novel trace metal isotope method quantifies “palaeo-sediment residence times” as proxy for catchment erosion • First continuous catchment erosion record for the last and current glacial-interglacial cycle in SE Australia • Link between catchment vegetation cover and erosion highlights the role of Australia as global carbon sink

Restoring soil carbon in marginal land of Indian Himalayas: Impact of crop intensification and conservation tillage.

Soil carbon (C) loss is the prime sign of land degradation, and C pools have a great impact on soil quality and climate change mitigation. Hence, a field experiment was conducted for three consecutive years to assess the impact of crop intensification and conservation tillage practices on changes in the C pool at different soil depths of marginal land of the Indian Himalayas. The experiment consisted of two intensified cropping systems viz., CS1-Summer maize (Zea mays L.) -rainy season maize-lentil (Lens esculenta L.) and CS2-Summer maize-rainy season maize-mustard (Brassica juncea (L.) Czern) and five tillage practices viz., No-till (NT); NT+live mulch of cowpea (NT+LMC); reduced tillage (RT); RT+LMC and conventional tillage (CT). Results revealed that CS2 produced significantly higher biomass, C retention efficiency (9.85%), and sequestrated greater C (0.42Mgha-1 yr-1) in the soil system than CS1. Of the various tillage practices, RT+LMC registered higher biomass and recycled greater biomass and C than those under other tillage practices. However, the highest soil organic carbon (SOC) content (7.03gkg-1) and pool (9.62Mgha-1) in 0-10cm depth were observed under NT+LMC. The non-labile C pool size under NT in 0-10cm and 10-20cm depths was significantly greater than those under CT. The NT+LMC sequestrated significantly higher SOC (0.57Mgha-1 yr-1) than other tillage practices. Thus, the study indicated that the adoption of an intensified maize-based system under RT+LMC or NT+LMC would increase SOC storage and C sequestration in marginal lands of the Indian Himalayas.

Effects of different long-term fertilization patterns on net carbon sink effect and economic benefits in double cropping rice paddy ecosystem in southern China

There is close relationship between fertilizer managements and net carbon (C) sink effect, economic benefits in rice paddy ecosystem. Based on a long-term (35-year) field experiment, we analyzed the effects of different fertilization patterns on soil C sequestration rate, C density of topsoil, annual C balance, and economic benefits in the double cropping rice paddy in southern China. There were four fertilization treatments, chemical fertilizer alone (MF), rice straw and chemical fertilizer (RF), 30% organic manure and 70% chemical fertilizer (OM), and without any fertilizer input as a control (CK). The results showed that soil C pool in the double cropping rice paddy field under different fertilization treatments changed from 216.02 to 866.74 kg·hm-2·a-1, and soil C pool under OM treatment were significantly higher than that of MF, RF and CK. The soil C sequestration rates in the double cropping rice paddy field under different fertilization treatments ranged from 51.5 to 650.7 kg·hm-2·a-1, and that of C density of topsoil was from 55.64 to 78.42 t·hm-2. The order of soil C sequestration rates and C density of topsoil was OM>RF>MF>CK. The change range of C adsorption in the double cropping rice paddy field ecosystem was from 4.42 to 9.32 t C·hm-2·a-1, with an order of OM>RF>MF>CK. Compared with the MF treatment, soil net C sink under OM and RF treatments increased by 27.6% and 13.6%, respectively. The change range of C cost material input ranged from 1.49 to 2.17 t C·hm-2·a-1, and that of annual economic benefits was from 1.30×103 to 7.83×103 yuan·hm-2·a-1 with an order of RF>OM>MF>CK. The net income of economic benefits of OM, RF and MF treatments were significantly higher than that of CK. Generally, soil C sequestration rate, C sink effect and annual economic benefits were increased by the long-term application of organic manure and rice straw returning together with chemical fertilizer, which could increase soil organic carbon storage in the double cropping rice paddy field of southern China.

Increasing the Environmental Sustainability of Greenhouse Vegetable Production by Combining Biochar Application and Drip Fertigation—Effects on Soil N2O Emissions and Carbon Sequestrations

Drip fertigation with reduced fertilizer and water inputs has been widely used in greenhouse vegetable production in China. However, farmers usually do not apply additional organic material with a high carbon content, although soil organic carbon (SOC) concentrations are mostly below the optimum level for vegetable production. Returning straw or biochar to fields is an effective strategy for sustainability and environmental friendliness. We tested whether drip fertigation, (DIF) combined with maize straw (DIF+S) or biochar (DIF+BC), is a suitable option to improve SOC sequestration over eight growing seasons, and how these options affect soil N2O emissions and yields or partial factor productivity of applied N (PFPN) of crops over three growing seasons. During the winter–spring growing season, DIF+BC significantly reduced soil N2O emission by 61.2% and yield-scaled N2O emission by 62.4%, while increasing the tomato yield and PFPN compared with DIF. Straw incorporation had similar trends but without significant effects. Conversely, straw and biochar incorporation increased N2O emission during the autumn–winter season. The structural equation model indicated N2O emission was dominantly driven by soil NH4+-N concentration, temperature and moisture. The N2O emission factor decreased significantly with increased PFPN. Moreover, the contribution of biochar to the increased SOC was approximately 78%, which was four times higher than that of straw incorporation. Overall, the results highlighted the potential of drip fertigation with biochar incorporation to mitigate N2O emissions, improve PFPN and significantly increase SOC storage, which could all contribute to maintaining environmental sustainability and soil quality of greenhouse vegetable production.

Subsoiling and plowing rotation increase soil C and N storage and crop yield on a semiarid Loess Plateau

Subsoiling loose subsoil, plowing loose topsoil, burying crop residue, the take turns used of subsoiling and plowing in years seem to be good methods to achieve the goal of regulating topsoil and subsoil structure and improving soil fertility and crop yield. However, the evaluation of the long-term effects of a subsoiling and plowing yearly rotation in a crop residue retention cropping system is lacking. Therefore, a 12-year (2007–2019) experiment was established to evaluate the influence of a subsoiling and plowing rotation with residue retention on water-stable aggregates (WSA), soil organic carbon (SOC), total nitrogen (TN) storage, and crop yield in a winter wheat-spring maize rotation field. Tillage treatment was 1-year subsoiling and 1-year plowing rotation (ST/CT), and continuous subsoiling (ST) and plowing (CT) were used as controls. During the 12-year experiment, the ST/CT rotation reduced the mean C input of winter wheat (5.4%) and spring maize (1.7%) at harvest compared with the ST treatment but significantly improved the mean C input of winter wheat (6.2%) and spring maize (10.9%) at harvest compared with the CT treatment. After 12 years of the experiment (2019), the ST/CT rotation significantly increased water-stable macroaggregates (6.6% and 7.7%) at 0–40 cm compared with the ST and CT treatments, respectively. In addition, the ST/CT rotation had a lower SOC (0.11 Mg·ha−1) and N (0.16 Mg·ha−1) storage at the 0–10 cm soil depth than the ST treatment. However, the ST/CT rotation had a higher SOC (0.51 and 2.77 Mg·ha−1) and N storage (0.11 and 0.18 Mg·ha−1) at the 10–20 and 20–40 cm soil depths than the ST treatment. When compared to the CT treatment, the ST/CT rotation significantly improved SOC and N storage at 0–10 cm (4.24 and 0.18 Mg·ha−1), 10–20 cm (0.50 and 0.14 Mg·ha−1), and 20–40 cm (2.66 and 0.22 Mg·ha−1), respectively. Additionally, the ST/CT rotation also significantly enhanced the yield of winter wheat (5.6% and 10.5%) and spring maize (8.4% and 12.7%) compared with the ST and CT treatments, respectively. Different tillage significantly influenced the yield stability and sustainability of winter wheat, but no marked differences were observed in spring maize. In addition, a nonlinear relationship indicated that maximal SOC storage-responsive C input levels ranged from 3580 kg·ha−1 to 6007 kg·ha−1 for winter wheat and spring maize. ST/CT rotation can increase SOC storage before C saturation to reach maximized yield. To improve and sustain nutrient storage and crop production in winter wheat-fallow-spring maize rotation fields, ST/CT rotation seems to be a more suitable tillage practice.

Improved soil structural stability under no-tillage is related to increased soil carbon in rice paddies: Evidence from literature review and field experiment

Improving soil structural stability (SSS) and soil organic carbon (SOC) are critical for soil health and environmental pollution mitigation. No-tillage alters many soil properties (e.g., SOC), however, its effects on SSS in rice paddies are unclear. Therefore, we used field experiment and meta-analysis to determine the effects of no-tillage on wet stability of aggregates (WSA), clay dispersibility (ClayDis), mean weight diameter (MWD), and aggregate SOC distribution and mineralization in rice paddies. The field experiment included four tillage practices: no-tillage, rotary tillage and moldboard plow tillage with rice straw retention (NTS, RTS and CTS respectively), and moldboard plow tillage with rice straw removal (CT). The WSA at 0–5 cm soil depth was significantly higher under NTS compared with CTS. The ClayDis at 5–10 cm soil depth under NTS was 36% lower ( P < 0.05) than CTS. The relationship between SOC and WSA fits a broken stick model, with an inflection point of clay/SOC ratio at 12.5. Higher SOC under no-tillage might result from the protection of >2 mm aggregates (macroaggregates) and lower SOC mineralization of < 2 mm aggregates. Additionally, the meta-analysis showed that no-tillage increased ( P < 0.05) the macroaggregate content, WSA and MWD. However, the current research regarding tillage effects on paddy ClayDis is insufficient. In rice paddies, the increased macroaggregate content may contribute to increasing SOC, which improves SSS under no-tillage. • No-tillage in rice cropping increased soil structural stability. • Aggregate stability increases with SOC content and its mineralization. • SOC mineralizability of <2 mm aggregates was low under no-tillage. • No-tillage increased SOC storage in >2 mm aggregates. • Carbon mineralization did not differ among aggregate size classes.