Greenhouse gases emission from soils under major crops in Northwest India

Carbon footprint of maize-wheat cropping system after 40-year fertilization

Two main challenges which human society faces for sustainable development goals are the maintenance of food security and mitigation of greenhouse gas (GHG) emissions. Here, we examined the impacts of six fertilization treatments including unfertilized control (CK), mineral nitrogen (N, 90 kg N ha-1), mineral N plus 30 kg P ha-1 phosphorus (NP), NP combined with 3.75 Mg ha-1 straw (NP + Str), farmyard manure (Man, 75 Mg ha-1), and NP combined with manure (NP + Man) on crop productivity and carbon emissions (soil GHG emission; GHGI, yield-based GHG intensity; NGHGB, net GHG balance; carbon footprint, CF) in a maize-wheat cropping system during two years (April 2018-June 2020) in a semi-arid continental climate after 40 years of fertilization in the Northwest China. Manure and straw increased total GHG by 38-60 % compared to the mineral fertilizers alone, which was mainly due to the 49-80 % higher direct emissions of carbon dioxide (CO2) rather than nitrous oxide (N2O). Compared to the N fertilizer alone, organic amendments and NP increased cumulative energy yield by 134-202 % but decreased GHGI by 38-55 %, indicating that organic fertilizers increased crop productivity at the cost of higher GHG emissions. When the soil organic carbon changes (ΔSOC) were accounted for in the C emission balance, manure application acted as a net C sink due to the NGHGB recorded with -123 kg CO2-eq ha-1 year-1. When producing the same yield and economic benefits, the manure and straw addition decreased the CF by 59-85 % compared to N fertilization alone. Overall, the transition from mineral to organic fertilization in the semi-arid regions is a two-way independent solution to increase agricultural productivity along with the reduction of C emissions.

Environmental imprints of agricultural and livestock produce: A scoping review from South Asian countries

BACKGROUND

Agricultural activities in 2020 have resulted in 5.5 billion tons of CO2 equivalent globally, which is expected to rise because the food system would have to grow 70% more food for the population in 2050. Research suggests that agricultural productivity in South Asian countries, will increase food security; however, the role of their food crops and livestock products in environmental imprints is uncertain. This review aimed to assess the environmental impacts resulting from pre- and post-production agricultural activities related to edible food crops and livestock products consumed in eight South Asian countries.

METHODS

Studies were retrieved using three databases (PubMed, Google Scholar and Science Direct) from 2011 to 2022. The protocol for this scoping review was not registered.

RESULTS

Twenty-seven studies met the inclusion criteria. Most studies were conducted in India. Twenty-four articles assessed greenhouse gases (GHG) emissions, followed by water footprints (n = 5), nitrogen and phosphorus (N&P) emissions (n = 4), and land requirements (n = 4). The production of rice and wheat was identified as a significant contributor to GHG emissions. In India, Bangladesh and Sri Lanka, the production of livestock (meat/bovine/shrimp and milk) was reported to be harmful to the environment. Inconclusive data were retrieved for other environment variables.

CONCLUSIONS

Diversification in food production and cultivating additional coarse cereals (millets) offer opportunities for GHG reduction. Nevertheless, more comprehensive and longitudinal studies for South Asian countries are essential to make precise conclusions and validate the present review.

Millets: The future crops for the tropics - Status, challenges and future prospects

Millets are small-grained nutritious minor cereal crops that are resistant to different abiotic stresses resulting from climate change. Despite their many benefits, millets have received limited attention in agricultural research, policies, and markets. Considering the importance of millets, recently the government many tropical countries including India and Bangladesh give more emphasis to millets cultivation and improvement. Moreover, Food and Agricultural Organization of the United Nations (FAO) declared 2023 to be the "International Years of Millets". In these connections, a details and updated review of the pros and cons of millets cultivation and its improvement in this region warrant due attention. The review therefore, examines the potential and main barriers to the adoption and promotion of millet cultivation in this region. These include limited research and development efforts, inadequate infrastructure and inputs, weak market linkages and demand, and insufficient awareness and knowledge about millets' nutritional and environmental benefits. This review also highlighted the prospects and strategies for scaling up millet cultivation in this region especially in Bangladesh. These include increasing public and private investment in research and extension services, strengthening farmers' organizations and market linkages, promoting millet-based value chains and products, and integrating millets into nation's food policy. The review concludes that millets might support equitable and sustainable agricultural growth, which would contribute to global food and nutritional security and could help attain the sustainable development goals (SDGs). However, achieving this potential will require concerted efforts from multiple stakeholders, including farmers, researchers and policymakers. The review emphasizes the need for a multi-disciplinary and multi-stakeholder approach that prioritizes innovation, inclusiveness, and sustainability. Lastly, the review highlights more investigation into the socioeconomic, environmental, and nutritional effects of millet production in this region with special emphasis on Bangladesh in order to support evidence-based policies and practices.

Implications of CO2 emissions on the main land and forest uses in the Brazilian Amazon

The emission of soil carbon dioxide (CO₂) in agricultural areas is a process that results from the interaction of several factors such as climate, soil, and land management practices. Agricultural practices directly affect the carbon dynamics between the soil and atmosphere. Herein, we evaluated the temporal variability (2020/2021 crop season) of soil CO₂ emissions and its relationship with related variables, such as the CO₂ flux model, enhanced vegetation index (EVI), gross primary productivity (GPP), and leaf area index (LAI) from orbital data and soil temperature, soil moisture, and soil CO₂ emissions from in situ collections from native forests, productive pastures, degraded pastures, and areas of high-yield potential soybean and low-yield potential soybean production. A significant influence (p < 0.01) was observed for all variables and between the different land uses and occupation types. September and October had lower emissions of soil CO₂ and low means of soil moisture and soil temperature, and no differences were observed among the treatments. On the other hand, there was a significant effect of the CO₂ flux model in productive pastures, high-yield potential soybean areas, and low-yield potential soybean areas. The months with the highest CO₂ flux values in the model, regardless of land use and land cover, were October and November, which is the beginning of the rainy season. There were positive correlations between soil CO₂ emissions and GPP (0.208), LAI (0.354), EVI (0.363), and soil moisture (0.280) and negative correlations between soil CO₂ emissions and soil temperature (-0.240) and CO₂ flux model (-0.314) values. Land use and land cover showed negative correlations with these variables, except for the CO₂ flux model variable. Soil CO₂ emission values were lower for high-yield potential soybean areas (averages from 0.834 to 6.835 μmol m^-2 s^-1) and low-yield potential soybean areas (from 0.943 to 5.686 μmol m^-2 s^-1) and higher for native forests (from 2.279 to 8.131 μmol m^-2 s^-1), whereas the opposite was true for the CO₂ flux model.

Pulse-based cropping systems for soil health restoration, resources conservation, and nutritional and environmental security in rainfed agroecosystems

Pulses are an important source of energy and protein, essential amino acids, dietary fibers, minerals, and vitamins, and play a significant role in addressing global nutritional security. The global pulse area, production, and average productivity increased from 1961 to 2020 (60 years). Pulses are usually grown under rainfed, highly unstable, and complex production environments, with substantial variability in soil and environmental factors, high year-to-year output variability, and variation in soil moisture. Since the last six decades, there is not much satisfactory improvement in the yield of pulses because of their cultivation in harsh environments, coupled with their continuous ignorance of the farmers and governments in policy planning. As a result, the global food supplies through pulses remained negligible and amounted to merely ~1.0% of the total food supply and 1.2% of the vegan food system. In this situation, protein-rich food is still a question raised at the global level to make a malnutrition-free world. Pulses are a vital component of agricultural biological diversity, essential for tackling climate change, and serve as an energy diet for vegetarians. Pulses can mitigate climate change by reducing the dependence on synthetic fertilizers that artificially introduce nitrogen (N) into the soil. The high demand and manufacture of chemical fertilizers emit greenhouse gases (GHGs), and their overuse can harm the environment. In addition, the increasing demand for the vegetal protein under most global agroecosystems has to be met with under a stressed rainfed situation. The rainfed agroecosystem is a shelter for poor people from a significant part of the globe, such as Africa, South Asia, and Latin America. Nearly, 83% [over 1,260 million hectares (ha)] of cultivated land comes under rainfed agriculture, contributing significantly to global food security by supplying over 60% of the food. In rainfed areas, the limitation of natural resources with the shrinking land, continuous nutrient mining, soil fertility depletion, declining productivity factor, constantly depleting water availability, decreasing soil carbon (C) stock, augmented weed menace, ecological instability, and reduced system productivity are creating a more challenging situation. Pulses, being crops of marginal and semi-marginal soils of arid and semi-arid climates, require less input for cultivation, such as water, nutrients, tillage, labor, and energy. Furthermore, accommodation of the area for the cultivation of pulses reduces the groundwater exploitation, C and N footprints, agrochemical application in the cropping systems, and ill effects of climate change due to their inherent capacity to withstand harsh soil to exhibit phytoremediation properties and to stand well under stressed environmental condition. This article focuses on the role of pulses in ecological services, human wellbeing, soil, environmental health, and economic security for advanced sustainability. Therefore, this study will enhance the understanding of productivity improvement in a system-based approach in a rainfed agroecosystem through the involvement of pulses. Furthermore, the present study highlighted significant research findings and policy support in the direction of exploring the real yield potential of pulses. It will provide a road map to producers, researchers, policymakers, and government planners working on pulses to promote them in rainfed agroecosystems to achieve the United Nations (UN's) Sustainable Development Goals (SDGs).

Significance of different milling methods on white proso millet flour physicochemical, rheological, and baking properties

Proso millet is a nutritious, sustainable, and gluten free food which is currently underutilized. They can be incorporated into the grain industry and provide much needed healthy alternatives. Efficient grinding method should be adopted for easy incorporation. This study aimed to investigate the effect of three different methods of grinding namely, roller milling (RM), pin milling (PM), and hammer milling (HM) on proso millet flour rheology and baking properties for food application. The milling flow sheet was developed toward the production of the quality whole grain flour. The particle size distribution of all the flours showed bi-modal distribution except for the RM flour. The PM produced the flour with the finest particles with geometric mean diameter of 82 μm. The study also revealed that starch damage in the PM flour (4.64%) was higher than RM (2.46%) and HM flour (2.51%). The nutritional composition was not significantly affected by different grinding methods. Pasting properties of the flour were also affected by the grinding method applied. Rapid Visco Analysis profile showed pin mill flour to have a higher peak viscosity (PV) (2,295 cP) compared to HM (2,065 cP) and RM flour (2,130 cP). Finally, this study demonstrated that the production of bread from proso millet flour with desirable quality and texture is possible. The grinding method did not affect the specific volume of bread loaves and C-cell characteristics. The specific volume of the breads ranged from 2.40 to 2.52 cm³ /g. This study will help in promoting and producing value-added proso millet food products with enhanced nutritional quality.

Trade-offs between grain yields and ecological efficiencies in a wheat-maize cropping system using optimized tillage and fertilization management on the North China Plain

Optimized fertilizer and tillage management can be an effective strategy for high ecological efficiencies as well as crop yields. The objective of this study was to assess the impact of diverse management practices on carbon footprint, and ecosystem services in a wheat-maize cropping system. An in situ field experiment field was conducted from 2018 to 2020 on the North China Plain, and six treatments were established: deep tillage (DT), shallow tillage (ST), no tillage (NT), deep tillage + adding organic fertilizer (DTF), shallow tillage + adding organic fertilizer (STF), and no tillage + adding organic fertilizer (NTF). The results showed that adding organic fertilizer and the deeper tillage depth caused higher direct CO₂ and N₂O emission fluxes. DTF treatment significantly increased carbon footprint either per-unit area (CFa) or per-unit net income (CFe). Compared with DT treatment, STF treatment had higher CFa but lower CFe by increasing net income through boosted crop yields. Besides, the highest ecosystem service values (ESV) were present in STF treatment during both 2 years (42,017.13 CNY ha^-1 and 43,352.03 CNY ha^-1). In conclusion, STF treatment was an optimal management practice to trade-off grain yields and ecological efficiencies in a wheat-maize cropping system. Furthermore, this study highlights that adding organic fertilizer could be an efficient option toward sustainable farmland utilization with high soil carbon sequestration capacity and high ESV.

Agricultural greenhouse gas emissions of an Indian village - Who's to blame: crops or livestock?

A carbon footprint assessment, combining various scales of analysis and including a territorial assessment, is proposed to estimate the greenhouse gas (GHG) emissions from crops and livestock in an Indian village impacted by both Green (for crops) and White (for milk) revolutions. It is based on the GHG assessment of 10 cropping systems, 8 livestock farming systems and 9 production systems using the comparative agriculture and Life Cycle Assessment (LCA) approaches. Results show that mineral fertilisation, irrigation and methane from paddy fields are the main drivers of emissions at plot level. Livestock farming systems emit from 4.7 tCO_2eq/female to 8.6 tCO_2eq/female, enteric fermentation being the first source of emission. Disparities at farm level are huge, ranging from 9 to 733 tCO_2eq. At village level, emissions yield 37 tCO_2eq/ha and livestock contributes to 60 % of GHG emissions. The high GHG emissions are a legacy of the Green and White Revolutions: the livestock population is high, fed on highly emissive fodder and concentrates and produces little milk. The results enhance our understanding of the share of carbon emissions from crops and livestock at farm and territorial level. They pinpoint the environmental and socio-economic downsides of livestock farming intensification.

Integrating major agricultural practices into the TRIPLEX-GHG model v2.0 for simulating global cropland nitrous oxide emissions: Development, sensitivity analysis and site evaluation

Nitrous oxide (N₂O) emissions from croplands are one of the most important greenhouse gas sources while the estimation of which remains large uncertainties globally. To simulate N₂O emissions from global croplands, the process-based TRIPLEX-GHG model v2.0 was improved by coupling the major agricultural activities. Sensitivity experiment was used to measure the impact of the integrated processes to modeled N₂O emission found chemical N fertilization have the highest relative effect sizes. While the coefficient of the NO₃^- consumption rate for denitrification (COE_dNO3), controlling the first step of the denitrification process was identified to be the most sensitive parameter based on sensitivity analysis of model parameters. The model performed well when simulating the magnitude of the daily N₂O emissions for 39 calibration sites and the continental mean of the parameters were used to producing reasonable estimations for the means of the measured daily N₂O fluxes (R² = 0.87, slope = 1.07) and emission factors (EFs, R² = 0.70, slope = 0.72) during the experiment periods. The model reliability was further confirmed by model validation. General trend of modeled daily N₂O emissions were reasonably consistent with the observations of selected validated sites. In addition, high correlations between the results of modeled and observed mean N₂O emissions (R² = 0.86, slope = 0.82) and EFs (R² = 0.66, slope = 0.83) from 68 validation sites were obtained. Further improvement on more detailed estimations for the variation of the environmental factors, management effects as well as accurate model input model driving data are required to reduce the uncertainties of model simulations. Consequently, our simulation results demonstrate that the TRIPLEX-GHG model v2.0 can reliably estimate N₂O emissions from various croplands at the global scale, which contributes to closing global N₂O budget and sustainable development of agriculture.

Seasonal Variations in Grain Yield, Greenhouse Gas Emissions and Carbon Sequestration for Maize Cultivation in Bangladesh

Rationale: Greenhouse gas (GHG) emissions from crop agriculture are of great concern in the context of changing climatic conditions; however, in most cases, data based on lifecycle assessments are not available for grain yield variations or the carbon footprint of maize. The current study aimed to determine net carbon emissions and sequestration for maize grown in Bangladesh. Methods: The static closed-chamber technique was used to determine total GHG emissions using data on GHG emissions from maize fields and secondary sources for inputs. A secondary source for regional yield data was used in the current study. GHG emission intensity is defined as the ratio of total emissions to grain yield. The net GHG emission/carbon sequestration was determined by subtracting total GHG emissions (CO2 eq.) from net primary production (NPP). Results: Grain yields varied from 1590 to 9300 kg ha−1 in the wet season and from 680 to 11,820 kg ha−1 in the dry season. GHG emission intensities were 0.53–2.21 and 0.37–1.70 kg CO2 eq. kg−1 grain in the wet and dry seasons, respectively. In Bangladesh, the total estimated GHG emissions were 1.66–4.09 million tonnes (MT) CO2 eq. from 2015 to 2020, whereas the net total CO2 sequestration was 1.51–3.91 MT. The net CO2 sequestration rates were 984.3–5757.4 kg ha−1 in the wet season and 1188.62–5757.39 kg ha−1 in the dry season. This study observed spatial variations in carbon emissions and sequestration depending on growing seasons. In the rice–maize pattern, maize sequestered about 1.23 MT CO2 eq. per year−1, but rice emitted about 0.16 MT CO2 eq. per year−1. This study showed potential spatiotemporal variations in carbon footprints. Recommendation: Special care is needed to improve maize grain yields in the wet season. Fertiliser and water use efficiencies need to be improved to minimise GHG emissions under changing climatic conditions. Efforts to increase the area under cultivation with rice–maize or other non-rice crop-based cropping systems are needed to augment CO2 sequestration. The generation of a regional data bank on carbon footprints would be beneficial for combating the impact of climate change.

Management Strategies to Mitigate N2O Emissions in Agriculture

The concentration of greenhouse gases (GHGs) in the atmosphere has been increasing since the beginning of the industrial revolution. Nitrous oxide (N2O) is one of the mightiest GHGs, and agriculture is one of the main sources of N2O emissions. In this paper, we reviewed the mechanisms triggering N2O emissions and the role of agricultural practices in their mitigation. The amount of N2O produced from the soil through the combined processes of nitrification and denitrification is profoundly influenced by temperature, moisture, carbon, nitrogen and oxygen contents. These factors can be manipulated to a significant extent through field management practices, influencing N2O emission. The relationships between N2O occurrence and factors regulating it are an important premise for devising mitigation strategies. Here, we evaluated various options in the literature and found that N2O emissions can be effectively reduced by intervening on time and through the method of N supply (30–40%, with peaks up to 80%), tillage and irrigation practices (both in non-univocal way), use of amendments, such as biochar and lime (up to 80%), use of slow-release fertilizers and/or nitrification inhibitors (up to 50%), plant treatment with arbuscular mycorrhizal fungi (up to 75%), appropriate crop rotations and schemes (up to 50%), and integrated nutrient management (in a non-univocal way). In conclusion, acting on N supply (fertilizer type, dose, time, method, etc.) is the most straightforward way to achieve significant N2O reductions without compromising crop yields. However, tuning the rest of crop management (tillage, irrigation, rotation, etc.) to principles of good agricultural practices is also advisable, as it can fetch significant N2O abatement vs. the risk of unexpected rise, which can be incurred by unwary management.

Global warming potential and energy dynamics of conservation tillage practices for different rabi crops in the Indo-Gangetic Plains

A field experiment was conducted during 2007-2019 under various rabi (winter) crops (viz., wheat, maize, barley and mustard) on a Vertisol in sub-tropical Indo-Gangetic Plains (IGP) with different tillage systems to assess energy indices, greenhouse gas (GHG) emission and carbon sustainability index in assured irrigated fields. The tillage systems were: no tillage sown by a zero till drill (NT), no tillage with retention of previous crop residues at 6 t ha^-1 and sowing by a happy turbo seeder (HT), and conventional tillage (CT) where sowing was performed by a multi-crop zero till drill after twice harrowing + twice tilling + once rotavator operations. Significantly higher input energy was observed in wheat followed by maize, barley and mustard. Among tillage systems, CT plots consumed higher input energy that was about 20, 21 to 22, 25 to 26 and 20-22% higher than HT and NT in wheat, maize, barley and mustard, respectively. However, output energy and energy use efficiency were highest in HT. The total GHG emission (kg CO₂ equivalent ha^-1) was highest in wheat (2,351) followed by maize (2,274), barley (1,859) and mustard (1,652). Among tillage systems, CT produced about 31-34%, 33-34%, 37-40% and 28-30% higher GHG emission than HT and NT under wheat, maize, barley and mustard, respectively. The CT plots had lower carbon sustainability index and carbon efficiency than ZT and HT in all crops. In short, HT recorded significantly higher energy use efficiency and lower global warming potential (GWP) than CT in all crops. Thus, HT could be a promising agro-technique for production of rabi crops in the IGP. Among rabi crops, barley production was energy efficient and had less GWP. In rabi crop production, the highest energy sources was mineral fertilizer use (25-49%) and second highest source was irrigation water (14-44%). These can be substituted with use of the organic sources of fertilizers and application of solar and wind power in irrigation, respectively.

Mitigation of yield-scaled greenhouse gas emissions from irrigated rice through Azolla, Blue-green algae, and plant growth-promoting bacteria

Irrigated transplanted flooded rice is a major source of methane (CH4) emission. We carried out experiments for 2 years in irrigated flooded rice to study if interventions like methane-utilizing bacteria, Blue-green algae (BGA), and Azolla could mitigate the emission of CH4 and nitrous oxide (N2O) and lower the yield-scaled global warming potential (GWP). The experiment included nine treatments: T1 (120 kg N ha-1 urea), T2 (90 kg N ha-1 urea + 30 kg N ha-1 fresh Azolla), T3 (90 kg N ha-1 urea + 30 kg N ha-1 Blue-green algae (BGA), T4 (60 kg N ha-1 urea + 30 kg N ha-1 BGA + 30 kg N ha-1 Azolla, T5 (120 kg N ha-1 urea + Hyphomicrobium facile MaAL69), T6 (120 kg N ha-1 by urea + Burkholderia vietnamiensis AAAr40), T7 (120 kg N ha-1 by urea + Methylobacteruim oryzae MNL7), T8 (120 kg N ha-1 urea + combination of Burkholderia AAAr40, Hyphomicrobium facile MaAL69, Methylobacteruim oryzae MNL7), and T9 (no N fertilizer). Maximum decrease in cumulative CH4 emission was observed with the application of Methylobacteruim oryzae MNL7 in T7 (19.9%), followed by Azolla + BGA in T4 (13.2%) as compared to T1 control. N2O emissions were not significantly affected by the application of CH4-oxidizing bacteria. However, significantly lower (P<0.01) cumulative N2O emissions was observed in T4 (40.7%) among the fertilized treatments. Highest yields were observed in Azolla treatment T2 with 25% less urea N application. The reduction in yield-scaled GWP was at par in T4 (Azolla and BGA) and T7 (Methylobacteruim oryzae MNL7) treatments and reduced by 27.4% and 15.2% in T4 and T7, respectively, as compared to the T1 (control). K-means clustering analysis showed that the application of Methylobacteruim oryzae MNL7, Azolla, and Azolla + BGA can be an effective mitigation option to reduce the global warming potential while increasing the yield.

Greenhouse gas emissions from inorganic and organic fertilizer production and use: A review of emission factors and their variability

Fertilizers have become an essential part of our global food supply chain and are necessary to sustain our growing population. However, fertilizers can also contribute to greenhouse gas (GHG) emissions, along with other potential nutrient losses in the environment, e.g. through leaching. To reduce this environmental impact, tools such as life cycle assessments and decision support systems are being used to aid in selecting sustainable fertilization scenarios. These scenarios often include organic waste-derived amendments, such as manures, composts and digestates. To produce an accurate assessment and comparison of potential fertilization scenarios, these tools require emission factors (EFs) that are used to estimate GHG emissions and that are an integral part of these analyses. However, such EFs seem to be very variable in nature, thereby often resulting in high uncertainty on the outcomes of the analyses. This review aims to identify ranges and sources of variability in EFs to provide a better understanding of the potential uncertainty on the outcomes, as well as to provide recommendations for selecting EFs for future studies. As such, an extensive review of the literature on GHG emissions from production, storage, transportation and application of synthetic fertilizers (N, P, K), composts, digestates and manures was performed. This paper highlights the high variability that is present in emissions data and confirms the great impact of this uncertainty on the quality and validity of GHG predictions related to fertilizers. Variability in EFs stem from the energy source used for production, operating conditions, storage systems, crop and soil type, soil nutrient content, amount and method of fertilizer application, soil bacterial community, irrigation method, among others. Furthermore, a knowledge gap exists related to EFs for potassium fertilizers and waste valorization (anaerobic digestion/composting) processes. Overall, based on this review, it is recommended to determine EFs on a case by case basis when possible and to use uncertainty analyses as a tool to better understand the impact of EF variability.

Effect of organic amendments on yield-scaled N2O emissions from winter wheat-summer maize cropping systems in Northwest China

The effect of dairy manure amendments to agricultural soil on the yield-scaled nitrous oxide (N2O) emissions remains unclear. We hypothesize that an optimum ratio of dairy manure to synthetic fertilizers leads to large nitrogen use efficiency (NUE) and small yield-scaled N2O emissions. The aims of this study were to (1) quantify the variations in the crop yields and N2O emissions from winter wheat-summer maize cropping systems in Northwest China, (2) determine the responses of the NUE and yield-scaled N2O emission to the ratio of organic materials to synthetic fertilizers, and (3) evaluate the relationship between the NUE and yield-scaled N2O emissions. Field measurements were conducted within long- and short-term fertilization experiments between the years of 2014 and 2016. Treatments included synthetic fertilizers, synthetic fertilizers plus crop residues, and synthetic fertilizers plus dairy manure at both sites. The annual grain yields and N2O emissions varied from 13.3 to 18.0 Mg ha-1 and from 1.3 to 3.6 kg N ha-1, respectively, across the treatments. The yield-scaled N2O emissions related negatively to the NUE, suggesting that agronomic aims of improving NUE are an effective approach to mitigate N2O emissions. The ratio of organic materials to synthetic fertilizers was not a significant limit on the NUE and yield-scaled N2O emissions. We conclude that organic amendments appeared to play a minor influence on the promotion of the NUE and N2O mitigation.

Crop yield and N2O emission affected by long-term organic manure substitution fertilizer under winter wheat-summer maize cropping system

Application of organic manure combined with synthetic fertilizer can maintain crop yield and improve soil fertility, but the long-term effects of substituting different proportions of synthetic fertilizers with organic manure on N₂O emission remain unclear. In this study, field experiments and DNDC model simulations were used to study the long-term effects of substituting synthetic fertilizers with organic manure on crop yield and N₂O emission. The field experiment was conducted at Guanzhong Plain, northern China, under a wheat-maize cropping system. Six treatments were included: no fertilization (CK); synthetic nitrogen (N), phosphorus (P) and potassium (K) fertilizers (NPK); and 25%, 50%, 75% and 100% of the synthetic N substituted by dairy manure (25%M, 50%M, 75%M, and 100%M), respectively. The DNDC model was calibrated using the field data from the NPK treatment from 2014 to 2017 and was validated for the other treatments. The results showed that the DNDC model can successfully simulate the crop yield (e.g. nRMSE < 5%) and annual N₂O emission (nRMSE < 20%). In addition, a 30-year simulation found that organic manure substitution treatments could maintain wheat yield well, and the yield variation between different years was small. However, relative to the NPK treatment, the maize yields for the first 6 and 7 years were lower under 50%M and 75%M, and under 100%M maize yields were reduced for the first 15 years. The long-term simulation showed that N₂O emission of fertilized treatment had an increasing trend over time, especially the 75%M treatment where the N₂O emission was higher than that of NPK treatment after 25 years of fertilization. The annual mean N₂O emission under different treatments was, in decreasing order, NPK > 25%M > 50%M > 75%M > 100%M > CK. The yield-scale N₂O emission and emission factor were highest for the NPK treatment. Considering crop yield, yield stability and N₂O emission, substitution of 25% synthetic fertilizer by organic manure can simultaneously ensure crop productivity and environmental protection under the tested environment.

Effects on Greenhouse Gas (CH4, CO2, N2O) Emissions of Conversion from Over-Mature Forest to Secondary Forest and Korean Pine Plantation in Northeast China

This study aimed to evaluate the seasonal variations of Greenhouse Gas fluxes (CH4, CO2, and N2O), Greenhouse Gas (GHG) emissions, and Global Warming Potential (GWP) over the extent of the regions and understand the controlling factors. CH4, CO2, and N2O fluxes were measured along with their environmental variables from the over-mature forest, Korean pine plantation, and five 60-year-old natural secondary forests in mountainous regions in Northeast China from May 2015 to April 2016. The results revealed that secondary forests, except for Betula platyphylla forest, significantly increased CH4 absorption by 19.6% to 51.0% and 32.6% to 67.0% compared with over-mature forest (OMF) and Korean pine plantation (KPP). Five secondary forests significantly increased CO2 flux by 32.9% to 78.6% and 14.1% to 53.4% compared with OMF and KPP, respectively. According to the annual statistics, the N2O fluxes had significant differences among seven forest types and decreased in the following order: mixed deciduous forest (MDF) > OMF > KPP > Populous davidiana forest (PDF) > hardwood forest (HWF) > Mongolian oak forest (MOF) > Betula platyphylla forest (BPF). The CH4 absorption and CO2 emission peaks occurred in summer, while the peak N2O fluxes occurred in spring. Stepwise multiple linear regression showed that CH4 and CO2 fluxes from soils were strongly influenced by air and soil temperature, soil volumetric water content (SVWC), nitrate nitrogen (NO3−-N), ammonium nitrogen (NH4+-N), and soil organic carbon (SOC) across the whole year. Air temperature, SVWC, pH, NO3−-N, and NH4+-N were the dominant factors controlling N2O fluxes from OMF and five secondary forests (except for BPF). No significant relationships were observed between these environmental factors and N2O fluxes from KPP and BPF. Additionally, the total cumulative CH4, CO2, and N2O fluxes were –13.37 t CH4 year−1, 41,608.96 t CO2 year−1, and 3.24 t N2O year−1, and the total cumulative GWP were 42,151.87 t CO2 eq year−1 through the whole year in seven forest types at the Maoershan Ecosystem Research Station in Northeast China. For the annual GWP per hectare, secondary forests and KPP averaged a higher GWP by 33.7%–80.1% and 17.9% compared with OMF. This indicates that the effects of early human activities have not been completely eliminated in the middle stage of KPP and secondary forests.

Effects on Carbon Sources and Sinks from Conversion of Over-Mature Forest to Major Secondary Forests and Korean Pine Plantation in Northeast China

The effects of replacing over-mature forest with secondary forests and plantations are significant for terrestrial ecosystem carbon (C) dynamics. However, the carbon balance and recovery time of this replacement process remain unclear. This study measured the fluxes of CH4 and CO2 in soils and the annual net C sequestration (ANCS) from seven ecosystems with different vegetation types (over-mature forest (OMF), Korean pine plantation (KPP), hardwood forest (HWF), Betula platyphylla forest (BPF), Populous davidiana forest (PDF), mixed deciduous forest (MDF), and Mongolian oak forest (MOF)) using the static chamber-gas chromatography method and the relative growth equation method. We examined the effects of environmental factors (e.g., air and soil temperature, soil volumetric water content (SVWC), soil pH, nitrate nitrogen (NO3−-N), ammonium nitrogen (NH4+-N), and soil organic carbon (SOC)) on CH4 and CO2 fluxes at the Maoershan Ecosystem Research Station in Northeast China. The carbon source or sink of OMF, KPP, and five secondary forests (HWF, BPF, PDF, MDF, and MOF) were then evaluated based on net ecosystem C balance. The results revealed that the mean annual CH4 fluxes varied between −0.046 and −0.077 mg m−2 h−1. The mean annual absorption of CH4 in the secondary forests and OMF were respectively 1.09–1.67 times and 1.11 times higher than that of KPP (0.046 mg m−2 h−1, p < 0.05). The mean annual CO2 fluxes varied between 140.425 and 250.023 mg m−2 h−1. The CO2 fluxes in the secondary forests and KPP soils were respectively 1.33–1.78 times and 1.16 times higher than that of OMF (140.425 mg m−2 h−1, p < 0.05). The CH4 and CO2 fluxes were mainly influenced by air and soil temperature, SVWC, soil pH, NO3−-N, NH4+-N, and SOC in Northeast China. The ANCS of vegetation (3.41 ± 0.27 − 6.26 ± 0.75 t C ha−1 y−1) varied widely among different forest types: KPP had the largest ANCS (6.26 ± 0.75 t C ha−1 y−1, which was higher than secondary forests and OMF by 1.20–1.84 times and 1.46 times, respectively, p > 0.05). Carbon sources and sinks were significantly different among the seven types of vegetation: OMF and KPP were observed to be the greatest C sinks, and secondary forests were shown to be the weakest carbon sinks or net C sources in the study region.

Relationships between soil organic matter pools and nitrous oxide emissions of agroecosystems in the Brazilian Cerrado

In the Brazilian Cerrado, despite the increasing adoption of no-till systems, there are still extended areas under conventional soil management systems that reduce soil carbon (C) and nitrogen (N) stocks and increase the emissions of greenhouse gases, such as nitrous oxide (N₂O). Conservation agroecosystems, such as no-till, have been proposed as a strategy to mitigate agriculture-induced climatic changes through reductions in N₂O emissions. However, the relationship between organic matter and N₂O emissions from soils under different agroecosystems is not yet clear. This study hypothesized that agroecosystems under no-till promote an accumulation of labile and stable SOM fractions along with a reduction of N₂O emissions. This study evaluated the effects of crop-rotation agroecosystems: i) on C and N pools and labile and stable SOM fractions; ii) on cumulative N₂O emissions; and iii) on the relationships between SOM fractions and N₂O emissions. The agricultural systems consisted of: (I) soybean followed by sorghum under no-tillage (NT1); (II) maize followed by pigeon pea under no-tillage (NT2); (III) soybean under conventional tillage followed by fallow soil (CT); (IV) and native Cerrado (CER). After CT for 18years, following the replacement of CER, the soil C stock in the 0-20cm layer was reduced by 0.64tha^-1year^-1. The no-till systems were more efficient in accumulating labile and stable C fractions with values close to those observed under CER, and were directly related to lower soil N₂O emissions. The cumulative pattern of N₂O emissions was inverse to that of the following SOM fractions: microbial biomass carbon, permanganate-oxidizable carbon, particulate organic carbon, inert carbon, and humic substances. Based on principal component analysis, the CT was generally separated from the other land use systems. This separation was strongly influenced by the low C contents in the different SOM fractions and higher N₂O emissions promoted by the CT.

Methane oxidation in lead-contaminated mineral soils under different moisture levels

Methane (CH₄) oxidation in soil reduces the concentration of this greenhouse gas due to the activity of methanotrophic bacteria. This process is influenced by chemical and physical parameters of soil. We tested the methanotrophic activity of selected mineral soils (Mollic Gleysol, Haplic Podzol, Eutric Cambisol) contaminated with lead (Pb) under different soil water potentials (pF 0; 2.2; 3.2). The heavy metal was added as PbCl₂ in two doses. Together with the initial content of Pb in soils, the final contents of heavy metal in different soils were 11.6 and 30.8 mg kg^-1 in Eutric Cambisol, 7.1 and 26.3 mg kg^-1 in Haplic Podzol, and 12.2 and 31.4 mg kg^-1 in Mollic Gleysol (dry mass of the soil is specified in all cases). The results showed relatively low sensitivity of methane oxidation to the addition of the heavy metal. The major factor controlling this process was soil water content, which in most cases turned out to be the most optimal at pF = 2.2.

Trade-off between soil organic carbon sequestration and nitrous oxide emissions from winter wheat-summer maize rotations: Implications of a 25-year fertilization experiment in Northwestern China

The primary aims of this study were to (i) quantify the variations in nitrous oxide (N₂O) emissions and soil organic carbon (SOC) sequestration rates under winter wheat-summer maize cropping systems in Guanzhong Plain and (ii) evaluate the impact of organic amendments on greenhouse gas mitigation over a long-term period. We measured N₂O fluxes during the maize season in 2015 under four fertilizer regimes in a long-term fertilization experiment. Soil was treated with only synthetic fertilizers in the maize season and with synthetic fertilizers, synthetic fertilizers plus crop residues and synthetic fertilizers plus low and high levels of dairy manure in the winter wheat season from 1990. The SOC content (0-20cm) was collected annually at the same site between 1990 and 2015. Synthesis of our measurements and previous observations (between 2000 and 2009) within the investigated agricultural landscape revealed that cumulative N₂O emissions increased with the SOC content following natural logarithm models during both the maize and winter wheat seasons (r²>0.77, p<0.001), implying a trade-off between N₂O emissions and SOC sequestration. The SOC content increased under all fertilizer regimes, and the dynamics were well fitted by the linear and logistic regression models (r²>0.74, p<0.001), indicating that all the fertilizer treatments in this study sequestered SOC. By applying these regression models, we estimated that the two manure-amended treatments accumulated a negative global warming potential (ranging from -1.9 to -12.9tCO₂-equivalentha^-1) over the past 25years. However, this benefit would most likely be offset by high N₂O emissions at saturated SOC levels before 2020. Our estimates suggest that organic amendments may not be efficient for greenhouse gas mitigation in Guanzhong Plain over a long-term period. We recommend efforts to inhibit N₂O production via denitrification as being critical to resolving the conflict between SOC sequestration and N₂O emissions.

Architects of nature: growing buildings with bacterial biofilms

In his text 'On Architecture', Vitruvius suggested that architecture is an imitation of nature. Here we discuss what happens when we begin using nature in architecture. We describe recent developments in the study of biofilm structure, and propose combining modern architecture and synthetic microbiology to develop sustainable construction approaches. Recently, Kolodkin-Gal laboratory and others revealed a role for precipitation of calcium carbonate in the maturation and assembly of bacterial communities with complex structures. Importantly, they demonstrated that different secreted organic materials shape the calcium carbonate crystals formed by the bacterial cells. This provides a proof-of-concept for a potential use of bacteria in designing rigid construction materials and altering crystal morphology and function. In this study, we discuss how these recent discoveries may change the current strategies of architecture and construction. We believe that biofilm communities enhanced by synthetic circuits may be used to construct buildings and to sequester carbon dioxide in the process.

Microalgae biofilm in soil: Greenhouse gas emissions, ammonia volatilization and plant growth

Microalgal biofilm in soils represents an alternative fertilization method for agricultural sustainability. In the present study, greenhouse gas emission, soil ammonia volatilization, and the growth of Pennisetum glaucum were evaluated under the effect of a microalgal biofilm, commercial urea, and a control (without application of a nitrogen source). CH₄ emissions were equal for the three treatments (p>0.05). CO₂ emissions significantly increased in microalgal biofilm treatment (p<0.01), which was also responsible for the highest N₂O emissions (p<0.01). The ammonia (NNH₃) volatilization losses were 4.63%, 18.98%, and 0.82% for the microalgal biofilm, urea, and control treatments, respectively. The main differences in soil characteristics were an increase in nitrogen and an increase in cation exchange capacity (p<0.01) caused by the algal biomass application to the soil. The soil organic matter content significantly differed (p<0.05) among the three treatments, with the microalgal biofilm treatment having the greatest increase in soil organic matter. Significant differences were observed for shoot dry matter mass and nitrogen content in the plants from both treatments where nitrogen sources were applied. All treatments differed from each other in leaf dry matter mass, with the urea treatment increasing the most. Chlorella vulgaris was the dominant microalgal specie in the soil.