Soil Organic Carbon Sequestration Rates Research Articles

Early impacts of marginal land‐use transition to Miscanthus on soil quality and soil carbon storage across Europe

AbstractMiscanthus, a C4 perennial rhizomatous grass, is a low‐input energy crop suitable for marginal land, which cultivation can improve soil quality and promote soil organic carbon (SOC) sequestration. In this study, four promising Miscanthus hybrids were chosen to evaluate their short‐term potential, in six European marginal sites, to sequester SOC and improve physical, chemical, and biological soil quality in topsoil. Overall, no differences among Miscanthus hybrids were detected in terms of impacts on soil quality and SOC sequestration. SOC sequestration rate after 4 years was of +0.4 Mg C ha−1 year−1, but land‐use transition from former cropland or grassland showed contrasting SOC sequestration trajectories. In unfertilized marginal lands, cultivation of high‐yielding Miscanthus genotypes caused a depletion of K (−216 kg ha−1 year−1), followed by Ca (−56 kg ha−1 year−1), Mg (−102 kg ha−1 year−1) and to a lesser extent of N. On the contrary, the biological turnover of organic matter increased the available P content (+164 kg P2O5 ha−1 year−1). SOC content was identified as the main driver of changes in biological soil quality. High input of labile plant C stimulated an increment of microbial biomass and enzymatic activity. Here, a novel approach was applied to estimate C input to soil from different Miscanthus organs. Despite the high estimated plant C input to soil (0.98 Mg C ha−1 year−1), with significant differences among sites and Miscanthus hybrids, it was not identified as a driver of SOC sequestration. On the contrary, initial SOC and nutrients (N, P) content, as well as their elemental stoichiometric ratios with C, were the key factors controlling SOC dynamics. Introducing Miscanthus on marginal lands impacts positively soil biological quality over the short term, but targeted fertilization plans are needed to secure crop yield over the long term as well as the C sink capacity of this perennial cropping system.

Eco-Sustainability of Soils in Baby-Leaf Crop Systems under Tunnel through the Application of C-Rich Inputs: Towards Combating Soil Degradation

Fresh-cut leafy vegetables are produced in Southern Italy in very intensive crop systems under tunnel greenhouses in which continuous cropping has triggered soil organic carbon (SOC) depletion and the risk of degradation of soil fertility. A two-year trial of soil organic amendment was carried out on a private farm producing baby-leaf crops on a very poor OC soil (<1%). Biowaste compost, two types of olive pomace composts and buffalo manure were compared to evaluate their ability to recover a positive SOC balance and sustain crop growth and yield. The effects on soil health and crop system were studied by measuring different aspects such as SOC stock change and SOC sequestration rate, soil microbial biomass and nine enzyme activities, yields of rocket and concentration of nitrates in leaves. Soil amendments were distributed once a year at doses of 15 and 30 Mg ha−1 as fresh matter without integration of mineral fertilizers. In our study, the SOC stock improved in the amended soils in a range of 4–6 Mg ha−1, except for dose 30 of buffalo manure, with the highest values where biowaste compost was applied. Our data showed an increase in biological parameters in all the amended soils with respect to Control. In soil amended with olive pomace, however, compost mineralization rates likely did not match crops’ nutrient needs so the yields of rocket were lower than with the biowaste compost and buffalo manure. Biowaste compost showed the best results as it balanced the best C conversion efficiency, the higher increment of SOC and yields of rocket.

Comparative Assessment of Inorganic Fertilizer and Farm Yard Manure Application on Yield, Sustainable Yield Index and Soil Physico-Chemical Properties in Cauliflower-Capsicum Cropping Sequence in Northern- Western Himalayas

ABSTRACT Continuous addition of inorganic fertilizer and farm yard manure (FYM) alone or in combination is necessary to assess the changes in yield and soil properties. Therefore, a study was conducted for consecutive two years on nutrient management with nine treatments viz. T1- control, T2-100% FYM (N equivalent basis), T3-100% N, T4-NP, T5-NK, T6-PK, T7-NPK, T8-100% NPK+ FYM (recommended Practice) and T9- 150% NPK+ FYM to assess the influence of different treatments on yield, sustainable yield index, soil physic-chemical properties and soil carbon stock and sequestration rate in cauliflower and capsicum cropping sequence. Results showed that the addition of farm yard manure alone or in a combination with chemical fertilizers contributed to higher soil organic stock and soil carbon sequestration rate. Application of 150% NPK + FYM improved the SYI of system by 49.4% over a control. This treatment increases soil carbon stock by 12.5% from 25.9 Mg ha−1 to 29.6 Mg ha−1 and recorded with maximum soil carbon sequestration rate, i.e. 2.21 Mg C m−3 year−1 over the 2 years. Thus, balanced fertilization of NPK and FYM is beneficial for the maintenance of soil physical health, improving CEC and macro and micronutrient levels.

Oilseed rape-rice rotation with recommended fertilization and straw returning enhances soil organic carbon sequestration through influencing macroaggregates and molecular complexity

The sequestration of soil organic carbon (SOC) is influenced by agricultural management practices. However, the mechanisms that underlie the impacts of diverse paddy-upland rotation systems and fertilization strategies on SOC sequestration remain to be elucidated. Within this study, we investigated the variations in SOC sequestration under oilseed rape-rice (OR) and wheat-rice (WR) rotations with various fertilization regimes (CK, without fertilization; EF, excessive fertilization; RF, recommended fertilization; and RF+S, recommended fertilization with straw returning) through a five-year field experiment. Crop C inputs, soil aggregate-associated organic C, SOC functional groups, and their importance in SOC sequestration were examined. The results revealed that both SOC stock and sequestration rate were significantly enhanced by the OR rotation and straw returning. Specifically, SOC stock and sequestration rates were 7.7–14.3% and 28.6–83.7% higher in the OR rotation compared to the WR rotation under the same fertilization treatment. In addition, SOC stocks and sequestration rates were 6.7–13.3% and 24.4–77.6% higher in the RF+S treatment compared to the RF treatment. However, excessive fertilization (EF) did not further promote SOC sequestration. The OR rotation also showed higher values of aggregate mean weight diameter (MWD) and large-macroaggregate C compared to the WR rotation, with increases of 7.7–14.1% and 4.7–33.8%, respectively. The nuclear magnetic resonance studies showed that the OR rotation exhibited an elevated abundance of aromatic C and a more intricate molecular configuration compared to the WR rotation. Furthermore, crop C input increased significantly with fertilization, and crop C input was the highest in the RF+S treatment. The aggregate MWD and large-macroaggregate C also significantly increased after fertilization. Partial least squares path modeling revealed that crop rotation affected SOC sequestration mainly through its effect on large-macroaggregate C and SOC molecular structure complexity, whereas fertilization mainly affected SOC sequestration though its effects on crop C inputs and large-macroaggregate C. We conclude that OR rotation combined with straw returning is an effective measure for enhancing SOC sequestration in paddy-upland rotation systems, contributing to mitigating climate change in agricultural systems.

Net greenhouse gas balance in U.S. croplands: How can soils be part of the climate solution?

Agricultural soils play a dual role in regulating the Earth's climate by releasing or sequestering carbon dioxide (CO2 ) in soil organic carbon (SOC) and emitting non-CO2 greenhouse gases (GHGs) such as nitrous oxide (N2 O) and methane (CH4 ). To understand how agricultural soils can play a role in climate solutions requires a comprehensive assessment of net soil GHG balance (i.e., sum of SOC-sequestered CO2 and non-CO2 GHG emissions) and the underlying controls. Herein, we used a model-data integration approach to understand and quantify how natural and anthropogenic factors have affected the magnitude and spatiotemporal variations of the net soil GHG balance in U.S. croplands during 1960-2018. Specifically, we used the dynamic land ecosystem model for regional simulations and used field observations of SOC sequestration rates and N2 O and CH4 emissions to calibrate, validate, and corroborate model simulations. Results show that U.S. agricultural soils sequestered Tg CO2 -C year-1 in SOC (at a depth of 3.5 m) during 1960-2018 and emitted Tg N2 O-N year-1 and Tg CH4 -C year-1 , respectively. Based on the GWP100 metric (global warming potential on a 100-year time horizon), the estimated national net GHG emission rate from agricultural soils was Tg CO2 -eq year-1 , with the largest contribution from N2 O emissions. The sequestered SOC offset ~28% of the climate-warming effects resulting from non-CO2 GHG emissions, and this offsetting effect increased over time. Increased nitrogen fertilizer use was the dominant factor contributing to the increase in net GHG emissions during 1960-2018, explaining ~47% of total changes. In contrast, reduced cropland area, the adoption of agricultural conservation practices (e.g., reduced tillage), and rising atmospheric CO2 levels attenuated net GHG emissions from U.S. croplands. Improving management practices to mitigate N2 O emissions represents the biggest opportunity for achieving net-zero emissions in U.S. croplands. Our study highlights the importance of concurrently quantifying SOC-sequestered CO2 and non-CO2 GHG emissions for developing effective agricultural climate change mitigation measures.

Effects of different tillage and residue management systems on soil organic carbon stock and grain yield of rice–wheat double cropping system

Of late, intensive agricultural practices are often associated with many negative implications for soil systems, such as decline in soil organic matter and biological diversity, and increase in the risk of soil erosion, and degradation of soil physical quality. However, conservation agriculture (CA) offers minimum soil disturbance, improving and creating more efficient use of natural resources, enhancing use efficiency of external inputs and increasing soil functioning, organic matter content, and biodiversity. However, CA practices need to be redefined at the specific field level or growing conditions to promote sustainable production system without deteriorating soil health, and to manage profitability. Therefore, a fixed-site field experiment was conducted to evaluate the effects of different tillage and residue management practices; CT0 (puddled transplanted rice followed by conventional tilled wheat sown with residue removal); CTR (puddled transplanted rice followed by conventional tilled wheat sown with residue retention); NT0 (direct seeded rice followed by zero-tilled wheat sown with residue removal); NTR (direct seeded rice followed by zero-tilled wheat sown with residue retention) on soil organic carbon (SOC) stock and grain yield of rice–wheat double cropping system. The results showed that the mean SOC stock increased by 31%, 21.9% and 15.3% and by 35.2%, 22% and 17% under NTR, CTR, and NT0 compared with CT0. Furthermore, the SOC sequestration rate in NTR was significantly higher than other treatments. Particulate organic carbon (POC) concentration was 58.4% higher in 0–15 cm than 15–30 cm soil layer, and the maximum concentration was recorded under NTR and minimum was under CT0. The highest average rice grain yield was recorded under CTR, which was 5.5%, 16.2% and 24.3% higher than CT0, NTR and NT0, respectively. Both NTR and CTR produced more average wheat yield, which was 8.4% and 8.5% higher than CT0 and NT0, respectively. Principal component analysis (PCA) also showed that cumulative cropping system yield and SOC were increased under CTR, NTR as compared to other treatments. Therefore, it can be drawn that residue retention could be a useful management practice to increase SOC stock and grain yield under both tillage practices in the rice–wheat cropping system.

Unlocking the potential of conservation agriculture for soil carbon sequestration influenced by soil texture and climate: A worldwide systematic review

Conservation Agriculture (CA) systems have gained significant attention as a sustainable cropping approach that not only improves crop yields but also contributes to climate change adaptation and mitigation through enhanced soil organic carbon (SOC) sequestration. However, a comprehensive understanding of the influence of soil texture and climate conditions on SOC sequestration under CA remains limited. To address this knowledge gap, we conducted a systematic review using the PRISMA method, analyzing data from 35 peer-reviewed articles encompassing 71 field experiments and 451 observations worldwide. Our findings demonstrate the substantial positive impact of CA on SOC sequestration, with an overall increase of approximately 78%. Remarkably, only a mere 2% of observations reported neutral effects, while 20% indicated adverse outcomes. Notably, SOC sequestration rates were highest in tropical regions experiencing dry winters, reaching an impressive 2.50 Mg/ha/year in the topsoil layers. Moreover, fine and moderate textured soils, such as clay, clay loam, loam, and clay sandy, exhibited higher SOC sequestration rates (20-27%) compared to coarse-textured soils dominated by sandy proportions (9%). These findings emphasize the significance of climate conditions and soil texture in shaping the impact of CA on SOC sequestration.

Impacts of reduced synthetic fertiliser use under current and future climates: Exploration using integrated agroecosystem modelling in the upper River Taw observatory, UK

The intensification of farming and increased nitrogen fertiliser use, to satisfy the growing population demand, contributed to the extant climate change crisis. Use of synthetic fertilisers in agriculture is a significant source of anthropogenic Greenhouse Gas (GHG) emissions, especially potent nitrous oxide (N2O). To achieve the ambitious policy target for net zero by 2050 in the UK, it is crucial to understand the impacts of potential reductions in fertiliser use on multiple ecosystem services, including crop production, GHG emissions and soil organic carbon (SOC) storge. A novel integrated modelling approach using three established agroecosystem models (SPACSYS, CSM and RothC) was implemented to evaluate the associated impacts of fertiliser reduction (10%, 30% and 50%) under current and projected climate scenarios (RCP2.6, RCP4.5 and RCP8.5) in a study catchment in Southwest England. 48 unique combinations of soil types, climate conditions and fertiliser inputs were evaluated for five major arable crops plus improved grassland. With a 30% reduction in fertiliser inputs, the estimated yield loss under current climate ranged between 11% and 30% for arable crops compared with a 20–24% and 6–22% reduction in N2O and methane emissions, respectively. Biomass was reduced by 10–25% aboveground and by <12% for the root system. Relative to the baseline scenario, soil type dependent reductions in SOC sequestration rates are predicted under future climate with reductions in fertiliser inputs. Losses in SOC were more than doubled under the RCP4.5 scenario. The emissions from energy use, including embedded emissions from fertiliser manufacture, was a significant source (14–48%) for all arable crops and the associated GWP20.

Maximizing the carbon sink function of paddy systems in China with machine learning

Developing low-carbon agriculture and alleviating the “carbon crisis” requires optimizing strategies that fully leverage the carbon sink function of paddy systems. Accurate assessment of the effects of various agricultural management practices (AMPs) on the carbon sink function of paddy systems is crucial to this end. Here, we have presented a soil organic carbon sequestration rate (SOCSR) database of paddy systems in China based on 1388 groups of experimental data from 143 peer-reviewed publications. We analyzed the impact trend of different AMPs on SOCSR, compared two traditional regression models, four classic machine learning models and two deep learning models, and established a data-driven SOCSR prediction model to quantify the impact of AMPs on SOCSR and provide the optimal strategies. Our model (Random Forest) had the characteristics of high accuracy (R2 = 0.71, RMSE = 0.53 Mg ha−1), strong flexibility, low time cost with a certain degree of interpretability for the regional scale of China. We found that inorganic N fertilizer, inorganic K fertilizer, organic fertilizer, tillage and residue management are relatively important AMPs for improving SOCSR. The carbon sink function of paddy systems would reach saturation when the application rate of inorganic N fertilizer, inorganic K fertilizer and organic fertilizer reached around 80 kg N ha−1, 40 kg K ha−1 and 2200 kg C ha−1, respectively. Compared to half residue returning and conventional tillage, full residue returning and no-tillage increased SOCSR by 39.8 % and 9.2 %, respectively. Our optimal combination of strategies could achieve SOCSR of 1.179 Mg ha−1 in paddy systems of China. Our work enables swift and precise evaluation of SOCSR in paddy systems, provides a new idea for assessing SOCSR of paddy systems on a regional scale, and serves as an essential part for the accurate assessment of the carbon footprint of rice production.

Rates of soil organic carbon change in cultivated and afforested sandy soils

Considerable advances have been made in the assessment and mapping of soil organic carbon stocks, but rates of change in carbon stocks remain to be quantified for many soils and ecosystems. We sampled 145 sandy soils (mostly Psamments) under permanent cultivation and forest. We used aerial imagery to determine the period of cultivation and to calculate changes in soil organic carbon stocks. Topsoil organic carbon stocks, including the A and O horizons, were highest in soils under forest which were never cultivated (36 Mg C ha−1) and lowest in soils under red pine with prior cultivation (31 Mg C ha−1). Average soil organic carbon stocks of the A horizons of cultivated soils were 33 Mg C ha−1. To meet the 4 per 1000 international initiative, these soils need to achieve a soil organic carbon sequestration rate of 0.1 Mg C ha−1 yr−1. A mean rate of change of −0.16 Mg C ha−1 year−1 was found. The A horizon thickness increased under cultivation, but soil organic carbon concentrations decreased leading to reduced soil organic carbon stocks. The decline in soil organic carbon stock could be explained by an increased rate of organic matter decomposition due to tillage, irrigation, nitrogen applications, and lower clay and silt contents. After about 70 years of afforestation with red pine, soil organic carbon stocks increased. The O horizon accrued organic carbon at a rate of +0.19 Mg ha−1 yr−1, but soil organic carbon stocks were lower in the A horizon compared to cultivated soils. Afforestation of abandoned cultivated fields maintained soil organic carbon in the A horizon and gained organic carbon in the O horizon, but the soil organic carbon stocks were below soils under forest which were never cultivated.

Annual greenhouse gas emissions from a rice paddy with different water-nitrogen management strategies in Central China

Current water-nitrogen (N) management strategies are necessary to be improved to increase crop productivity while reducing environmental costs. However, the effects of improved water-N management strategies on paddy CH4 and N2O emissions simultaneously generated during the growing and non-growing seasons have not been explored. Therefore, in this study, four water-N management practices—urea plus conventional irrigation (UREA+CI), urea plus alternate wetting-drying irrigation (UREA+AWD), controlled-release N fertilizer plus CI (CRNF+CI), and CRNF plus AWD (CRNF+AWD)—were evaluated in a 3-year field experiment following a randomized complete block design with three replications each. The results demonstrated that during rice growing seasons, CH4 emissions significantly decreased by 12.6–44.9% under UREA+AWD and by 17.2–32.1% under CRNF+CI, compared to UREA+CI, respectively, and CRNF+SWD showed the highest mitigation potential. N2O emissions were reduced in CRNF treatments (CRNF+CI and CRNF+AWD) but increased by replacing CI with AWD during rice growing seasons, suggesting the potential effects of water regimes on N2O emissions. Furthermore, AWD and CRNF reduced CH4 emissions during the land preparation period before the late rice growing season and the fallow period, whereas CRNF treatments triggered the release of N2O in the fallow period. Moreover, there were no significant differences in soil organic carbon sequestration rates among the treatments. The results indicated that AWD, CRNF and their combination significantly reduced annual net total greenhouse gas emissions without yield loss. Collectively, this study unravels the potential of alternative water-N management strategies to improve rice yields while minimizing GHG emissions in double rice cropping systems.

Differences of SOC storage and stability between soil layers influenced by long-term fertilization in a typical paddy soil of Southern China

BackgroundThe contribution of long-term fertilization to soil organic carbon (SOC) storage has been of great concern. To assess the effects of long-term fertilization on SOC storage and stability in top and sub-soil layers, soil samples were collected from a 29-year field experimental station in a typical paddy soil in southern China. The SOC storage of whole soil and SOC fractions was quantified at three soil depths (0–20, 20–40, 40–60 cm) under four treatments: no fertilization (Control), a combination of nitrogen, phosphorus and potassium (NPK), double the rates of NPK (2NPK), NPK plus manure (NPKM).ResultsThe increase of Cinput-total was significantly higher than that of SOC storage among different treatments (p < 0.05), indicating that soil fixation of exogenous carbon is limited. Besides, the SOC accumulation and sequestration rates patterned as NPKM > 2NPK > NPK, and these rates were higher at 0–20 cm depth as compared to other depth intervals. Furthermore, for the whole profile, the SOC storage of active pool was higher in the Control (39.6 t C ha−1) than in other treatment (36.2 t C ha−1, p < 0.05). Whereas, fertilization increased the SOC storage of passive pool, ranked as NPKM > 2NPK≈NPK > Control (p < 0.05), indicating that fertilization, especially organic combined with inorganic fertilization, improved SOC stability. From the perspective of soil layers, the difference of SOC storage among treatments for passive pool was mainly resulted from the difference at surface soil, and for active pool were the deeper layers. Additionally, manure application increased the difference among soil layers.ConclusionThis study concluded that non-fertilized treatment could improve the SOC storage of active pool especially in deep soil layers, while fertilization especially manure application could improve the SOC storage and stability in surface soil and increased the difference among soil layers.Graphical

Alfalfa–organic amendments impact soil carbon sequestration and its lability in reclaimed loess

AbstractSoils derived from loess are fertile but susceptible to accelerated degradation in response to agricultural practices. The objective of our study was to evaluate the long‐term effects of alfalfa (Medicago sativa L.) integrated with contrasting organic amendments (29 years) to rejuvenate degraded loess via total soil organic carbon (SOC) sequestration. The replicated study was conducted in concrete lysimeter plots (2 m long × 1 m wide × 60 cm deep) filled with degraded loess materials followed by planting of alfalfa with cattle manure (60 Mg/ha) or vermicompost (27 Mg/ha) amendments. After 29 years, SOC concentration increased by 5.3–6.2‐fold under alfalfa–organic amendments compared to the control. A similar impact of alfalfa–organic amendments was observed on the humic acid, fulvic acid, and humin concentrations. There was an overestimation of SOC stocks (151 ± 48 kg/ha) when equivalent depth was used compared to equivalent mass of soil. While the SOC sequestration rates were 614 ± 129, 710 ± 69, and 744 ± 161 kg/ha/year at 0–10 cm depth under alfalfa, alfalfa–manure, and alfalfa–vermicompost treatments, respectively, the SOC sequestration rates decreased with depth. Significantly higher values of carbon pool index (CPI) and carbon management index (CMI) under alfalfa–organic amendments justified our results associated with the SOC sequestration; however, the SOC lability (CL) decreased under alfalfa–organic amendments, when compared to the control. A significant nonlinear inverse relationship (R2 = 0.80) between the CPI and CL suggested that SOC sequestration is significantly dependent on its lability or vice versa. Our results suggested that the impact of alfalfa–organic amendments significantly rejuvenated the degraded loess soils via SOC sequestration.

Conservation agriculture impacts on soil carbon sequestration under a cotton (Gossypium hirsutum)-wheat (Triticum aestivum) system in the Indo-Gangetic plains

Despite many studies reporting conservation agriculture (CA) impacts on soil organic carbon (SOC) sequestration, the impacts of long-term permanent bed planting under CA on SOC sequestration are rarely reported. Hence, this study assessed the permanent bed planted CA impacts on SOC sequestration rates in 0–30 and 30–60 cm soil depths under a cotton (Gossypium hirsutum L.)-wheat (Triticum aestivum L.) system in the Indo-Gangetic Plains (IGP). The treatments comprised diverse combinations of tillage and residue retention (R), viz. conventional tillage (CT), narrow bed, narrow bed + R, broad bed, broad bed + R, flat bed + R and flat bed. Results indicated that the total SOC stock was ~32, 31 and 29% higher in CA plots than in CT plots (farmers' practice), in 0–30 cm soil depth. The SOC sequestration rate (over CT plots) in the CA plots was ~0.76 Mg C/ha/yr. The broad bed + R, narrow bed + R and flat bed + R plots had appreciably high total SOC sequestration (~0.24 Mg C/ha/yr) compared to CT plots in deep soil layer (30–60 cm). The yield data (2-year mean basis) was recorded highest in the broad bed + R (3.48 tonnes/ha and 8.11 tonnes/ha for cotton and wheat, respectively) and flat bed + R (3.38 tonnes/ha and 8.46 tonnes/ha for cotton and wheat, respectively) treatments showing a positive impact of the adoption of long-term CA in the IGP. Thus, adopting raised beds with residue retention has great potential for higher carbon sequestration and improving yields and can be recommended for sustainable intensification of arable lands in the region.

Irrigation schedule impact on greenhouse gas mitigation, carbon sequestration, and yield improvement of double rice-cropping systems in southern China

The development of water-saving irrigation in paddy soils is crucial because of the increasing demand for water resources. There is a need to improve the understanding of water use strategies that save water and reduce greenhouse gas (GHG) emissions without causing yield losses in double rice-cropping systems. The current study was conducted to examine the net global warming potential (NGWP) and net greenhouse gas intensity (NGHGI) based on the net GHG emissions, including soil organic carbon (SOC) change and indirect emissions (IEs). An experiment was conducted under flood irrigation (FI), shallow irrigation (SI), and intermittent irrigation (II) conditions. The average double rice yields under the SI and II treatments were significantly higher than those under FI by 4.7% and 12.1%, respectively. The SI and II treatments could save 44% and 67% of irrigation water in the entire double-cropping rice-growing season, respectively. However, the SOC sequestration rate over 4 years was not significantly different among the three irrigation regimes. Compared to FI, the annual methane (CH4) emissions decreased by 34% and 45% under SI and II, respectively. In contrast, nitrous oxide (N2O) emissions under SI and II increased by 27% and 50%, respectively. IEs were nearly the same among the three irrigation regimes, with fertilizer use as the top contributor, and followed the order FI > SI > II. The NGWP and NGHGI decreased by 37% and 44%, respectively, under II compared to FI. In conclusion, water-saving irrigation strategies, especially the II practice, are an effective method that can simultaneously achieve great success in saving water, increasing rice production, and reducing GHG emissions.

Impact of land use/cover change and slope gradient on soil organic carbon stock in Anjeni watershed, Northwest Ethiopia.

Today's agri-food systems face the triple challenge of addressing food security, adapting to climate change, and reducing the climate footprint by reducing the emission of greenhouse gases (GHG). In agri-food systems, changes in land use and land cover (LULC) could affect soil physicochemical properties, particularly soil organic carbon (SOC) stock. However, the impact varies depending on the physical, social, and economic conditions of a given region or watershed. Given this, a study was conducted to quantify the impact of LULC and slope gradient on SOC stock and C sequestration rate in the Anjeni watershed, which is a highly populated and intensively cultivated area in Northwest Ethiopia. Seventy-two soil samples were collected from 0-15 and 15-30cm soil depths representing four land use types and three slope gradients. Soil samples were selected systematically to match the historical records (30years) for SOC stock comparison. Four land use types were quantified using Landsat imagery analysis. As expected, plantation forest had a significantly (p < 0.05) higher SOC (1.94Mgha-1) than cultivated land (1.38Mgha-1), and gentle slopes (1-15%) had the highest SOC (1.77Mgha-1) than steeper slopes (> 30%). However, higher SOC stock (72.03Mgha-1) and SOC sequestration rate (3.00Mgha-1year-1) were recorded when cultivated land was converted to grassland, while lower SOC stock (8.87Mgha-1) and sequestration rate (0.77Mgha-1year-1) were recorded when land use changed from cultivation to a plantation forest. The results indicated that LULC changes and slope gradient had a major impact on SOC stock and C sequestration rate over 30years in a highly populated watershed. It is concluded that in intensively used watersheds, a carefully planned land use that involves the conversion of cultivated land to grassland could lead to an increase in soil C sequestration and contributes to reducing the carbon footprint of agri-food systems.

Simulation-based assessment of the soil organic carbon sequestration in grasslands in relation to management and climate change scenarios

Soil organic carbon (SOC) is crucial for the quality and productivity of terrestrial ecosystems and its sequestration plays an important role in mitigating climate change. Understanding the effects of agricultural management under future climate on the SOC balance helps decision making in environmental policies. Thereby, grasslands will play a key role, since future climate change may prolong the vegetation period.We used 24 representative grassland sites in Germany to assess the SOC balance obtained from the CANDY model in relation to ten management regimes, 18 future climate change scenarios and different soil types. Simulations were conducted over a period of 110 years.For most of the selected grassland sites an increase in both air temperature and precipitation was observed in the future climate. The effect of management on the SOC balance largely exceeded the effect of soil type and climate. An increasing management intensity (i.e. three to five cuts) generally increased the SOC balance, while extensive management (i.e. two or fewer cuts) lead to SOC losses. The seasonal variation of precipitation was the most important climate metric, with increased SOC sequestration rates being observed with increasing growing season precipitation. Clay soils had the potential for both highest gains and highest losses depending on management and precipitation. Given an overall lower SOC storage potential in sands and loams, the SOC balance in those soil types varied the least in response to climate change.We conclude that fostering SOC sequestration is possible in grassland soils by increasing management intensity, which involves increased fertilizer input and field traffic. This however may stand in conflict with other policy aims, such as preserving biodiversity. Multicriterial assessments are required to estimate the nett greenhouse gas balance and other aspects associated with these management practices at a farm scale.

SOC sequestration affected by fertilization in rice-based cropping systems over the last four decades

Enhancing soil organic carbon (SOC) stocks through fertilization and crop rotation will contribute to sustaining crop productivity and mitigating global warming. In this study, we analyzed the differences in total SOC stocks and their driving factors in the topsoil (0–20 cm) with various fertilization measures in two puddled lowland rice-based cropping systems (i.e., rice-wheat rotation and double rice rotation systems) over the last four decades from seven long-term experiments in the Yangtze River catchment. The soil types include Cambisol, Luvisol, and Anthrosol. The treatments include no fertilizer application (CK), application of chemical nitrogen, phosphorus and potassium fertilizers (NPK) and a combination of NPK and manure applications (NPKM). Every year, field was ploughed to a depth of 15–20 cm before wheat sowing and rice transplanting. Residue was removed after plant harvesting. Results showed that during the last four decades, the average crop grain yield ranged from 1,151 ± 504 kg ha−1 yr−1 under CK treatment to 7,553 ± 1,373 kg ha−1 yr−1 under NPKM treatment. The topsoil SOC stock significantly increased by 8.6 t ha−1 on average under NPKM treatment in rice-wheat system and by 2.5–6.4 t ha−1 on average under NPK and NPKM treatments in double rice system as compared with CK. A higher SOC sequestration rate and a longer SOC sequestration duration were found in NPKM treatment than that in NPK treatment in both cropping systems. The highest SOC stock ratio (SOC stock in fertilizer treatments to CK) was observed under the NPKM treatment in both cropping systems, though no significant difference was found between these two cropping systems. However, the fertilization-induced relative increase of the SOC stock was 109.5% and 45.8% under the NPK and NPKM treatments, respectively in the rice-wheat system than that in the double rice system. This indicates that the rice-wheat system is more conducive for SOC sequestration. RF and SEM analyses revealed that the magnitude and influencing factors driving SOC sequestration varied between two systems. In the double rice system, continuous flooding weakens the influence of precipitation on SOC sequestration and highlights the importance of soil properties and C input. In contrast, soil properties, C input and climate factors all have important impacts on SOC sequestration in rice-wheat system. This study reveals that the rice-wheat system is more favorable for SOC sequestration despite its lower C input compared to the double rice system in China’s paddies.

Modeling impacts of saltwater intrusion on methane and nitrous oxide emissions in tidal forested wetlands.

Emissions of methane (CH4 ) and nitrous oxide (N2 O) from soils to the atmosphere can offset the benefits of carbon sequestration for climate change mitigation. While past study has suggested that both CH4 and N2 O emissions from tidal freshwater forested wetlands (TFFW) are generally low, the impacts of coastal droughts and drought-induced saltwater intrusion on CH4 and N2 O emissions remain unclear. In this study, a process-driven biogeochemistry model, Tidal Freshwater Wetland DeNitrification-DeComposition (TFW-DNDC), was applied to examine the responses of CH4 and N2 O emissions to episodic drought-induced saltwater intrusion in TFFW along the Waccamaw River and Savannah River, USA. These sites encompass landscape gradients of both surface and porewater salinity as influenced by Atlantic Ocean tides superimposed on periodic droughts. Surprisingly, CH4 and N2 O emission responsiveness to coastal droughts and drought-induced saltwater intrusion varied greatly between river systems and among local geomorphologic settings. This reflected the complexity of wetland CH4 and N2 O emissions and suggests that simple linkages to salinity may not always be relevant, as non-linear relationships dominated our simulations. Along the Savannah River, N2 O emissions in the moderate-oligohaline tidal forest site tended to increase dramatically under the drought condition, while CH4 emission decreased. For the Waccamaw River, emissions of both CH4 and N2 O in the moderate-oligohaline tidal forest site tended to decrease under the drought condition, but the capacity of the moderate-oligohaline tidal forest to serve as a carbon sink was substantially reduced due to significant declines in net primary productivity and soil organic carbon sequestration rates as salinity killed the dominant freshwater vegetation. These changes in fluxes of CH4 and N2 O reflect crucial synergistic effects of soil salinity and water level on C and N dynamics in TFFW due to drought-induced seawater intrusion.

Impacts of land use conversions on soil organic carbon in a warming-induced agricultural frontier in Northern Ontario, Canada under historical and future climate

Land conversion from forest to agriculture in higher latitude regions such as the Great Clay Belt of northern Ontario, Canada is expected to intensify due to warming. It is critical to minimize soil organic carbon (SOC) loss, but there is limited understanding of best land management practices for these Northern agricultural frontiers. We conducted a measurement campaign to assess changes in SOC after land conversion from native forest to either permanent pasture or to arable cropping by measuring SOC content (0–60 cm) at six farms with different land uses over the past 68 years (1950–2018). The Denitrification-Decomposition (DNDC) model was validated for historical SOC trends and then used to assess the impacts of future climate change on crop yields, SOC stocks, and SOC sequestration rates from 1954 to 2070 under three Shared Socio-economic Pathways (SSPs) scenarios from the Coupled Model Intercomparison Project Phase 6. Three land uses (1) continuous barley-oats (BO), (2) continuous Legume hay-BO, (3) continuous Pasture; and two land use conversions (4) pasture from 1954 to 2014 and then converted to BO from 2015 to 2070 (Pasture » BO) and (5) BO from 1954 to 2014 and then converted to pasture from 2015 to 2070 (BO » Pasture) were considered. Averaged across all six farms, the measured SOC stocks 68 years after conversion from forest were 22.7 and 25.3% higher under pasture than under forest and arable cropping, respectively. The DNDC demonstrated good performance in simulating yields of annual crops, legume hay and pasture as well as SOC stocks across all sites. Under future climate scenarios, higher SOC stocks were predicted for all land use conversions relative to the historical period, except for Pasture » BO. Under different land use, predicted SOC stocks were highest for continuous pasture, followed by BO » Pasture, Pasture » BO, Legume hay-BO and lowest for continuous BO. The DNDC predicted that the SOC sequestration rate would decrease for all land uses in the period 2015–2070 relative to 1954–2014, except for BO » Pasture. The predicted change declined from 0.35 to 0.22–0.28 Mg C ha−1 yr−1 for continuous pasture, but when change in management occurred from BO to pasture the rate of SOC gain increased. This underscores the potential role of pasture and crop diversification in avoiding SOC losses in agricultural frontiers induced by climate-warming.