Mitigating greenhouse gas emissions from irrigated rice cultivation through improved fertilizer and water management

Ways to mitigate greenhouse gas production from rice cultivation

Rice cultivation boasts a rich historical legacy, serving as the primary sustenance for over 50% of the global population. However, the cultivation process gives rise to the emission of methane (CH4) and nitrous oxide (N2O), two potent greenhouse gases. Notably, the global warming potential (GWP) of CH4 and N2O surpasses CO2 by 27-30 times and 273 times over 100 years, respectively. Addressing this environmental challenge necessitates exploring technical approaches and management strategies to curb gas emissions while sustaining rice yields. Several critical factors have been identified and analyzed for their potential to mitigate greenhouse gas production during rice cultivation. These include water management, fertilizer management, biochar application, cultivar selection, straw management, modified planting methods, and integration of new energy machinery. A comprehensive understanding and implementation of these methods can contribute significantly to achieving a dual objective: reducing emissions and maintaining optimal rice yields. Looking ahead, a synergistic integration of these diverse methods and management approaches holds promise for more effective results. Furthermore, the intricate water networks associated with rice cultivation should be carefully considered in the overall strategy. By adopting a holistic approach that addresses both emission reduction and sustainable water usage, the future of rice cultivation can be shaped to align with environmental stewardship and food security.

Impact of crop rotation and tillage operations on mitigating greenhouse gas emissions and evaluation of sustainability index in rice- wheat-green gram cropping system of north Bihar

In North Bihar (NB), the conventional rice-wheat cropping system has led to soil, water, and environmental degradation, alongside low profitability, threatening sustainability. To address these concerns, a thorough field research was conducted over the course of three years to assess different methods of tillage and crop establishment in a rice, wheat, and greengram cycle. The experiment involved five scenarios with different combinations of crop rotation, tillage techniques, seeding procedures, fertilizer use, and irrigation strategies. Uncertainty analysis showed no significant change in mean and variance estimation among seven scenario replications at 5% significance level. Compared to traditional farming (SN-1), managing DSR-rice (SN-5) increased profitability by 17.56%, improved energy use efficiency (EUE) by 32.16%, and reduced irrigation by 24.76% and global warming potential (GWP) by 23.46%. Similarly, substituting zero tillage wheat (ZTW) SN-5 resulted in comparable profitability gains (18.25%) and significant improvements in irrigation (10 %), EUE (+48.65%), and GWP (-20 %) compared to SN-1. Green gram ZT also showed increased profitability (17.35%), with notable improvements in EUE (+38.31%) and GWP (-12.92%) compared to SN-1. Principal component and correlation analyses revealed relationships between total energy inputs, yields, economic returns, and sustainability indices, highlighting the benefits of crop rotation and tillage practices in optimizing resource use. The study suggests that compared to conventional systems, significant improvements in productivity, profitability, energy-use efficiency, and environmental mitigation can be achieved with Crop Rotation and Tillage Operations techniques.

Paddy rice methane emissions, controlling factors, and mitigation potentials across Monsoon Asia

Rice is a staple food for more than half of humanity, and 90 % of rice is grown and consumed in Asia. However, paddy rice cultivation creates an ideal environment for the production and release of methane (CH4). How to estimate regional CH4 emissions accurately and how to mitigate them efficiently have been of key concern. Here, with a machine learning method, we investigate the spatiotemporal changes, the major controlling factors and mitigation potentials of paddy rice CH4 emissions across Monsoon Asia at a resolution of 0.1° (∼10 km). Spatially CH4 emissions are highly heterogeneous, with the Indo-Gangetic Plain, Deltas of the Mekong, and Yangtze River Basin as the hotspots. Nationwide, China, India, Bangladesh and Vietnam are the major emitters. Straw applied on season is a critical controlling factor for CH4 emission in rice fields. The single-season rice contributes to over 80 % of the total emissions. CH4 emissions from Monsoon Asia have notably declined since 2007. Three mitigation strategies, including water management techniques, off-season straw return, and straw to biochar, may reduce CH4 emissions by 27.66 %, 23.78 %, and 21.79 %, respectively, with the most effective strategy being rice cultivation type-specific and environment-specific. Our findings gain new insights into CH4 emissions and mitigations across Monsoon Asia, providing evidence to adopt precise mitigation strategies based on rice cultivation types and local environment.

Novel annual nitrogen management strategy improves crop yield and reduces greenhouse gas emissions in wheat-maize rotation systems under limited irrigation

Excessive irrigation and nitrogen application have long seriously undermined agricultural sustainability in the North China Plain (NCP), leading to declining groundwater tables and intensified greenhouse gas (GHG) emissions. Developing low-input management practices that meet the growing food demand while reducing environmental costs is urgently needed. Here, we developed a novel nitrogen management strategy for a typical winter wheat-summer maize rotation system in the NCP under limited irrigation (wheat sowing irrigation only (W0) or sowing and jointing irrigation (W1)) and low nitrogen input (360 kg N ha-1, about 70 % of traditional annual nitrogen input). Novel nitrogen management strategy promoted efficient nitrogen fertilizer uptake and utilization by both crops via optimization of nitrogen fertilizer allocation between the two crops, i.e., increasing nitrogen inputs to wheat (from 180 to 240 kg N ha-1) while reducing nitrogen inputs to maize (from 180 to 120 kg N ha-1). Three-year field study demonstrated that integrated management practices combining novel nitrogen management strategy with limited irrigation increased annual yields and PFPN by 1.9-5.7 %, and reduced TGE by 55-68 kg CO2-eq ha-1 and GHGI by 2.2-10.3 %, without any additional cost. Our results provide agricultural operators and policymakers with practical and easy-to-scalable integrated management strategy, and offer key initiative to promote grain production in the NCP towards agriculture sustainable intensification with high productivity and efficiency, water conservation and emission reduction.

A global meta-analysis of yield-scaled N2 O emissions and its mitigation efforts for maize, wheat, and rice

Maintaining or even increasing crop yields while reducing nitrous oxide (N2 O) emissions is necessary to reconcile food security and climate change, while the metric of yield-scaled N2 O emission (i.e., N2 O emissions per unit of crop yield) is at present poorly understood. Here we conducted a global meta-analysis with more than 6000 observations to explore the variation patterns and controlling factors of yield-scaled N2 O emissions for maize, wheat and rice and associated potential mitigation options. Our results showed that the average yield-scaled N2 O emissions across all available data followed the order wheat (322 g N Mg-1 , with the 95% confidence interval [CI]: 301-346) > maize (211 g N Mg-1 , CI: 198-225) > rice (153 g N Mg-1 , CI: 144-163). Yield-scaled N2 O emissions for individual crops were generally higher in tropical or subtropical zones than in temperate zones, and also showed a trend towards lower intensities from low to high latitudes. This global variation was better explained by climatic and edaphic factors than by N fertilizer management, while their combined effect predicted more than 70% of the variance. Furthermore, our analysis showed a significant decrease in yield-scaled N2 O emissions with increasing N use efficiency or in N2 O emissions for production systems with cereal yields >10 Mg ha-1 (maize), 6.6 Mg ha-1 (wheat) or 6.8 Mg ha-1 (rice), respectively. This highlights that N use efficiency indicators can be used as valuable proxies for reconciling trade-offs between crop production and N2 O mitigation. For all three major staple crops, reducing N fertilization by up to 30%, optimizing the timing and placement of fertilizer application or using enhanced-efficiency N fertilizers significantly reduced yield-scaled N2 O emissions at similar or even higher cereal yields. Our data-driven assessment provides some key guidance for developing effective and targeted mitigation and adaptation strategies for the sustainable intensification of cereal production.

Effects of integrated nutrient management and urea deep placement on rice yield, nitrogen use efficiency, farm profits and greenhouse gas emissions in saline soils of Bangladesh

Soil salinity is one of the major yield-limiting factors in the coastal ecosystems of Bangladesh. An efficient fertilizer management practice and selection of appropriate crop cultivars could play a crucial role in improving yield and promoting low-carbon agriculture across saline soils. A two-year multi-location field experiment was conducted during the Boro (dry) season (December-April) to investigate the effects of fertilizer management and rice cultivar selection on rice yield, economic viability, and global warming potential (GWP) in coastal saline soils of Bangladesh. The study included seven fertilizer treatments with varying nitrogen rates and sources, as well as two rice cultivars (BRRI dhan67 and BRRI dhan88). The results showed that integrated nutrient management-2 (INM-2) significantly (p < 0.05) increased rice yield and nitrogen use efficiency compared to other treatments for both BRRI dhan67 and BRRI dhan88. Similarly, INM-2 gave a higher return on fertilizer investment and marginal benefit-cost ratio than other treatments in both locations and under both cultivars. BRRI dhan67 significantly (p < 0.05) increased rice yield relative to BRRI dhan88 by 21 % and 52 % at the BRRI farm and Kaliganj in Satkhira, respectively. The cost-dominant analysis excluded BRRI dhan88 and all fertilizer treatments, except urea deep placement (UDP) and INM-2, from consideration in both locations. Consequently, INM-2 and UDP proved to be economically viable in both locations, with INM showing a higher marginal rate of return than UDP in BRRI dhan67. In terms of environmental sustainability, UDP significantly (p < 0.05) reduced GWP and yield-scaled emissions of CH4 by 31 % and 38 % without causing yield loss compared to INM-2. Similarly, BRRI dhan67 significantly (p < 0.05) reduced GWP and yield-scaled emissions of CH4 by 5 and 22 % compared to BRRI dhan88. These findings suggest that selecting salt-tolerant rice cultivars and implementing appropriate fertilizer management practices can enhance economic profitability, ensure food security, and mitigate the adverse effects of climate change in coastal saline soils.

Environment-friendly nitrogen management practices in wetland paddy cultivation

A large amount of nitrogen (N) fertilizer is required for paddy cultivation, but nitrogen use efficiency (NUE) in paddy farming is low (20–40%). Much of the unutilized N potentially degrades the quality of soil, water, and air and disintegrates the functions of different ecosystems. It is a great challenge to increase NUE and sustain rice production to meet the food demand of the growing population. This review attempted to find out promising N management practices that might increase NUE while reducing the trade-off between rice production and environmental pollution. We collected and collated information on N management practices and associated barriers. A set of existing soil, crop, and fertilizer management strategies can be suggested for increasing NUE, which, however, might not be capable to halve N waste by 2030 as stated in the “Colombo Declaration” by the United Nations Environment Program. Therefore, more efficient N management tools are yet to be developed through research and extension. Awareness-raising campaign among farmers is a must against their misunderstanding that higher N fertilizer provides higher yields. The findings might help policymakers to formulate suitable policies regarding eco-friendly N management strategies for wetland paddy cultivation and ensure better utilization of costly N fertilizer.

Biochar with Inorganic Nitrogen Fertilizer Reduces Direct Greenhouse Gas Emission Flux from Soil

Agricultural waste can have a catastrophic impact on climate change, as it contributes significantly to greenhouse gas (GHG) emissions if not managed sustainably. Swine-digestate-manure-derived biochar may be one sustainable way to manage waste and tackle GHG emissions in temperate climatic conditions. The purpose of this study was to ascertain how such biochar could be used to reduce soil GHG emissions. Spring barley (Hordeum vulgare L.) and pea crops in 2020 and 2021, respectively, were treated with 25 t ha^-1 of swine-digestate-manure-derived biochar (B₁) and 120 kg ha^-1 (N₁) and 160 kg ha^-1 (N₂) of synthetic nitrogen fertilizer (ammonium nitrate). Biochar with or without nitrogen fertilizer substantially lowered GHG emissions compared to the control treatment (without any treatment) or treatments without biochar application. Carbon dioxide (CO₂), nitrous oxide (N₂O), and methane (CH₄) emissions were directly measured using static chamber technology. Cumulative emissions and global warming potential (GWP) followed the same trend and were significantly lowered in biochar-treated soils. The influences of soil and environmental parameters on GHG emissions were, therefore, investigated. A positive correlation was found between both moisture and temperature and GHG emissions. Thus, biochar made from swine digestate manure may be an effective organic amendment to reduce GHG emissions and address climate change challenges.

The impact of irrigation modes on agricultural water-energy‑carbon nexus

Despite the tremendous contribution of irrigated agriculture in addressing global food security, there is still confusion for farmers and governments about the choice of irrigation mode owing to the drastic environmental impacts of irrigation, including water shortage, energy crisis, and global warming. Exploring the agricultural water-energy‑carbon (WEC) nexus under different irrigation modes helps to accomplish the multi-objective of water & energy saving and carbon emission reduction. In this paper, a conceptual framework was nominated to evaluate the water & energy consumption and carbon emissions for winter wheat irrigation at township level and quantitatively discuss the complex interaction by the coupling coordination degree (CCD) of the WEC system under different irrigation modes in Henan Province, China. We discovered that irrigation modes profoundly affect water and energy consumption and carbon emissions in agriculture, as well as the spatial distribution of CCD from WEC system. Townships under irrigation mode with diversion and irrigation projects as the primary method (WDI) clustered together in the north and east with highest water consumption and carbon emissions, while townships under irrigation mode with rain-fed agriculture as the primary method (PI) accumulated in the west and south with lower water consumption and carbon emissions. Meanwhile, the CCD of the WEC nexus system was in basic coordination (0.40) and showed an unbalanced spatial distribution pattern with high in the southeast and low in the northwest. By comparing four irrigation modes, the coupling level of the WEC nexus system under irrigation mode with groundwater irrigation as the primary method (GI) was better and PI mode was the least ideal. This study helps to further understand agricultural WEC nexus under different irrigation modes and provide references for local governments in selecting appropriate irrigation modes to realize water-energy saving and carbon emission reduction in agricultural activities.

Temperature-Related N2O Emission and Emission Potential of Freshwater Sediment

Nitrous oxide (N2O) is a major radiative forcing and stratospheric ozone-depleting gas. Among natural sources, freshwater ecosystems are significant contributors to N2O. Although temperature is a key factor determining the N2O emissions, the respective effects of temperature on emitted and dissolved N2O in the water column of freshwater ecosystems remain unclear. In this study, 48 h incubation experiments were performed at three different temperatures; 15 °C, 25 °C, and 35 °C. For each sample, N2O emission, dissolved N2O in the overlying water and denitrification rates were measured, and N2O-related functional genes were quantified at regular intervals. The highest N2O emission was observed at an incubation of 35 °C, which was 1.5 to 2.1 factors higher than samples incubated at 25 °C and 15 °C. However, the highest level of dissolved N2O and estimated exchange flux of N2O were both observed at 25 °C and were both approximately 2 factors higher than those at 35 °C and 15 °C. The denitrification rates increased significantly during the incubation period, and samples at 25 °C and 35 °C exhibited much greater rates than those at 15 °C, which is in agreement with the N2O emission of the three incubation temperatures. The NO3− decreased in relation to the increase of N2O emissions, which confirms the dominant role of denitrification in N2O generation. Indeed, the nirK type denitrifier, which constitutes part of the denitrification process, dominated the nirS type involved in N2O generation, and the nosZ II type N2O reducer was more abundant than the nosZ I type. The results of the current study indicate that higher temperatures (35 °C) result in higher N2O emissions, but incubation at moderate temperatures (25 °C) causes higher levels of dissolved N2O, which represent a potential source of N2O emissions from freshwater ecosystems.

Ratoon rice with direct seeding improves soil carbon sequestration in rice fields and increases grain quality

Increasing both carbon (C) sequestration and food production is essential for a sustainable future. However, increasing soil C sequestration or graining yield/quality in rice (Oryza sativa L.) systems has been a tradeoff in that pursuing one goal may compromise the other goal. Field experiments were designed to evaluate methane emission and grain yield in two rice systems in southern China, including the traditional double rice with a seedling transplanting system and innovative ratoon rice with a direct seeding system. Grain yield, grain quality, methane (CH₄) emission, and total organic carbon (TOC) loss rate were investigated, and yield-scaled CH₄ gas emission was assessed. It is found that double rice has a higher grain yield than ratoon rice. However, the grain quality (processing, appearance of chalkiness degree and chalky grain percentage, and nutritional quality) of ratoon rice is superior to double rice, especially the ratoon crop. The yield-scaled CH₄ emission of ratoon rice (0.06 kg kg^-1) decreased by 49.29% than double rice (0.12 kg kg^-1) throughout the growth period. Compared with the TOC loss rate of double rice (2.95 g kg^-1), the rate of ratoon rice was lower (1.97 g kg^-1). As a result, ratoon rice with direct seeding can not only improve grain quality but also mitigate yield-scaled CH₄ gas emission and TOC loss rate of rice fields. Therefore, we suggest to use ratoon rice with a direct seeding technique to promote agricultural C sequestration.

Perspectives on Converting Keratin-Containing Wastes Into Biofertilizers for Sustainable Agriculture

Keratin-containing wastes become pollution to the environment if they are not treated properly. On the other hand, these wastes can be converted into value-added products applicable to many fields. Organic fertilizers and biofertilizers are important for sustainable agriculture by providing nutrients to enhance the growth speed of the plant and production. Keratin-containing wastes, therefore, will be an important resource to produce organic fertilizers. Many microorganisms exhibit capabilities to degrade keratins making them attractive to convert keratin-containing wastes into valuable products. In this review, the progress in microbial degradation of keratins is summarized. In addition, perspectives in converting keratin into bio- and organic fertilizers for agriculture are described. With proper treatment, feather wastes which are rich in keratin can be converted into high-value fertilizers to serve as nutrients for plants, reduce environmental pressure and improve the quality of the soil for sustainable agriculture.

Impact of Land Management Scale on the Carbon Emissions of the Planting Industry in China

A change in agricultural land management scale leads to the recombination and adjustment of production factors, which have an important impact on agricultural carbon emissions. There are few studies on the connection between the scale of land management and agricultural carbon emissions. In this study, we empirically examined the relationship between planting scale and agricultural carbon emissions using the threshold model, which allows the data to endogenously generate several regimes identified by the thresholds. The results showed that from 2003 to 2018, carbon emissions from planting first increased and then decreased, reaching their highest in 2015. Across the whole country in the main rice- and wheat-producing regions, the scale of planting land has a threshold effect on agricultural carbon emissions, showing an inverted “U” shape. Carbon sinks and natural disasters significantly affected planting carbon emissions in the above three regions. The amount of fiscal support for agriculture significantly affects planting carbon emissions in the national and main wheat-producing regions, while peasants’ per capita income significantly affects planting carbon emissions in the main rice- and wheat-producing regions. This study provides policy makers with new ideas, in that continuously expanding the scale of agricultural land management is conducive to reducing agricultural carbon emissions.

Can the Adjustment of China's Grain Purchase and Storage Policy Improve Its Green Productivity?

While the sustainability of grain production has been extensively studied, there have been few studies focusing on the impact of grain policy adjustment on its sustainable production, and the quantitative relationship between these two aspects and the internal mechanism is not completely clear. The main objective of this paper was to explore the impact of grain purchase and storage policy (GPSP) adjustment on its green productivity by expounding the evolution logic and influence mechanism of GPSP. Therefore, taking maize production as an example, this paper constructs the analysis framework of the evolution logic and influence mechanism, and the super-epsilon-based measure model (Super-EBM) is adopted to measure maize green productivity (MGP) in main producing areas from 1997 to 2019, then two groups of difference-in-differences (DID) models are constructed to study the influence of the temporary purchase and storage policy (TPSP) and the producer subsidy policy (PSP) on MGP. The main conclusions include: the implementation of TPSP reduces MGP in Heilongjiang, Jilin, Liaoning and Inner Mongolia (experimental group), whereas the implementation of PSP improves MGP in these provinces is due to the difference in policy effects under the different regulatory objectives and measures; under the demonstration effect of two policies, the increase in effective irrigation and agricultural financial expenditure are important factors to improve MGP, but the backwardness of agricultural mechanization has been hindering the improvement of MGP; after the reform from TPSP to PSP, the continuous increase in production capacity hinders the improvement of MGP under the support effect, the impacts of farmers’ income and agricultural production price on MGP both shift from negative to positive under the wealth effect, and the influence of production agglomeration on MGP shifts from negative to positive under the siphon effect. The excessive implementation of GPSP has seriously affected the sustainability of grain production, thus, this study has certain practical significance and guiding value. The paper emphasizes that the effective way to achieve sustainable food production is to combine the adjustment of GPSP with improving the subsidy mechanism, enhancing the agricultural mechanization and maintaining the appropriate scale of operation.