• Energy Research

ABSTRACTBiochar amendments in rice‐wheat systems are sustainable for reducing GHGs (greenhouse gases) and improving soil health but the widespread adoption of biochar faces economic challenges. To address limitation, a novel biochar‐based urea was formulated for environmental and cost advantages. A pot experiment within a rice‐wheat rotation was conducted to evaluate comparative effects of biochar‐based urea (CKBU), biochar + urea (BCU), and biochar‐based urea + biochar (BCBU) over conventional mineral fertilizer (CKU) on soil ammonia (NH3) volatilization, GHG emissions, soil structure, and crop productivity. Furthermore, fertilizer N fate was tracked using the 15N isotope during wheat season. The results indicated that compared to CKU, CKBU, BCU, and BCBU treatments significantly mitigated NH3 volatilization by 22%–31% during the rice season, and a 19% reduction was observed under the BCBU treatment during the wheat season due to the response of N‐cycling microorganisms. Regarding GHG emissions, the CKBU, BCU, and BCBU treatments significantly decreased the global warming potential (GWP) value by 49%–55% during the rice season and by 26%–45% during the wheat season, compared to CKU. Additionally, CKBU enhanced 15N use efficiency by 29% during wheat season, without affecting the rice season. The economic performance indicated that applying BU alone offered a net economic benefit, whereas biochar amendment led to a net economic loss. However, biochar amendment improved SOC and aggregation structure, with a significant increase in macroaggregate distribution over 50% compared to CKU and CKBU. Therefore, BU with small portions of biochar can be as effective in reducing NH3 emissions and mitigating GHG emissions as the use of a large quantity of biochar. Additionally, the BCBU did not show additional synergistic benefits regarding emission reduction or yield enhancement. Therefore, shifting biochar to BU could be a cost‐effective approach to achieving sustainable productivity in rice‐wheat crop rotation systems.

L'agriculture représente environ 11 % des émissions nationales de gaz à effet de serre (GES) de la Chine. Grâce à l'adoption de meilleures pratiques de gestion spécifiques à la région, les agriculteurs chinois peuvent contribuer à la réduction des émissions tout en maintenant la sécurité alimentaire de leur grande population (>1 300 millions). Cet article présente les résultats d'une évaluation ascendante visant à quantifier le potentiel technique des mesures d'atténuation pour l'agriculture chinoise à l'aide d'une méta-analyse de données provenant de 240 publications pour les terres cultivées, 67 publications pour les prairies et 139 publications pour le bétail, et fournit le scénario de référence pour l'analyse des coûts des mesures d'atténuation identifiées. Les options de gestion présentant le plus grand potentiel d'atténuation pour le riz ou les systèmes de culture à base de riz sont le travail de conservation, l'irrigation contrôlée ; le remplacement de l'urée par du sulfate d'ammonium, l'application d'inhibiteurs d'azote (N), l'application d'engrais à teneur réduite en azote, la culture intégrée du riz, du poisson et du canard et l'application de biochar. Une réduction de 15 % de l'application moyenne actuelle d'engrais azotés synthétiques pour le riz en Chine, soit 231 kg N ha−1, entraînerait une diminution de 12 % des émissions directes d'oxyde nitreux (N2O) dans le sol. L'application combinée d'engrais chimiques et organiques, le travail de conservation, l'application de biochar et l'application réduite d'azote sont des mesures possibles qui peuvent réduire les émissions globales de GES des systèmes de culture en montagne. Les apports d'engrais conventionnels pour les légumes de serre représentent plus de 2 à 8 fois la demande optimale en nutriments des cultures. Une réduction de 20 à 40 % de l'application d'engrais azotés sur les cultures maraîchères peut réduire les émissions de N2O de 32 à 121 %, sans avoir d'impact négatif sur le rendement. L'une des mesures d'atténuation les plus importantes pour les prairies agricoles pourrait être la conversion de terres cultivées à faible rendement, en particulier sur les pentes, en terres arbustives ou en prairies, ce qui est également une option prometteuse pour réduire l'érosion des sols. En outre, l'exclusion du pâturage et la réduction de l'intensité du pâturage peuvent augmenter la séquestration du COS et réduire les émissions globales tout en améliorant les prairies largement dégradées. Pour la production animale, où le fourrage de mauvaise qualité est couramment nourri, l'amélioration de la gestion des pâturages et de la qualité de l'alimentation peut réduire les émissions de méthane (CH4) de 11 % et 5 % en moyenne. Les compléments alimentaires peuvent réduire davantage les émissions de CH4, les lipides (réduction de 15 %) et les tanins ou saponines (réduction de 11 %) présentant le plus grand potentiel. Nous suggérons également les mesures d'atténuation les plus rentables sur le plan économique, en nous appuyant sur les travaux connexes sur la construction de courbes de coûts marginaux de réduction pour le secteur. La agricultura representa aproximadamente el 11% de las emisiones nacionales de gases de efecto invernadero (GEI) de China. A través de la adopción de las mejores prácticas de gestión específicas de la región, los agricultores chinos pueden contribuir a la reducción de emisiones mientras mantienen la seguridad alimentaria para su gran población (>1300 millones). Este documento presenta el resultado de una evaluación ascendente para cuantificar el potencial técnico de las medidas de mitigación para la agricultura china utilizando el metanálisis de datos de 240 publicaciones para tierras de cultivo, 67 publicaciones para pastizales y 139 publicaciones para ganado, y proporciona el escenario de referencia para el análisis de costos de las medidas de mitigación identificadas. Las opciones de manejo con mayor potencial de mitigación para el arroz o los sistemas de cultivo a base de arroz son la labranza conservadora, el riego controlado; el reemplazo de urea con sulfato de amonio, la aplicación de inhibidores de nitrógeno (N), la aplicación reducida de fertilizantes de N, el cultivo integrado de arroz-piscifactoría y la aplicación de biochar. Una reducción del 15% en la aplicación promedio actual de fertilizantes sintéticos de N para el arroz en China, es decir, 231 kg de N ha−1, daría como resultado una disminución del 12% en las emisiones directas de óxido nitroso (N2O) del suelo. La aplicación combinada de fertilizantes químicos y orgánicos, la labranza conservadora, la aplicación de biocarbón y la aplicación reducida de N son posibles medidas que pueden reducir las emisiones generales de GEI de los sistemas de cultivo de tierras altas. Los insumos de fertilizantes convencionales para hortalizas de invernadero son más de 2–8 veces la demanda óptima de nutrientes de los cultivos. Una reducción del 20–40% en la aplicación de fertilizantes de N a los cultivos de hortalizas puede reducir las emisiones de N2O en un 32-121%, sin afectar negativamente el rendimiento. Una de las medidas de mitigación más importantes para los pastizales agrícolas podría ser la conversión de tierras de cultivo de bajo rendimiento, particularmente en laderas, a tierras de arbustos o pastizales, que también es una opción prometedora para disminuir la erosión del suelo. Además, la exclusión del pastoreo y la reducción de la intensidad del pastoreo pueden aumentar el secuestro de COS y disminuir las emisiones generales, al tiempo que mejoran los pastizales en gran medida degradados. Para la producción ganadera, donde se alimenta comúnmente el forraje de mala calidad, mejorar la gestión del pastoreo y la calidad de la dieta puede reducir las emisiones de metano (CH4) en un 11% y un 5%, en promedio. Los suplementos dietéticos pueden reducir aún más las emisiones de CH4, con lípidos (reducción del 15%) y taninos o saponinas (reducción del 11%) mostrando el mayor potencial. También sugerimos las medidas de mitigación económicamente más rentables, basándose en el trabajo relacionado con la construcción de curvas de costos de reducción marginal para el sector. Agriculture accounts for approximately 11% of China's national greenhouse gas (GHG) emissions. Through adoption of region-specific best management practices, Chinese farmers can contribute to emission reduction while maintaining food security for its large population (>1300 Million). This paper presents the outcome of a bottom–up assessment to quantify technical potential of mitigation measures for Chinese agriculture using meta-analysis of data from 240 publications for cropland, 67 publications for grassland and 139 publications for livestock, and provides the reference scenario for the cost analysis of identified mitigation measures. Management options with greatest mitigation potential for rice, or rice-based cropping systems are conservation tillage, controlled irrigation; replacement of urea with ammonium sulphate, nitrogen (N) inhibitor application, reduced N fertilizer application, integrated rice-fish-duck farming and biochar application. A 15% reduction in current average synthetic N fertilizer application for rice in China i.e., 231 kg N ha−1, would result in 12% decrease in direct soil nitrous oxide (N2O) emissions. Combined application of chemical and organic fertilizer, conservation tillage, biochar application and reduced N application are possible measures that can reduce overall GHG emissions from upland cropping systems. Conventional fertilizer inputs for greenhouse vegetables are more than 2–8 times the optimal crop nutrient demand. A 20–40% reduction in N fertilizer application to vegetable crops can reduce N2O emissions by 32–121%, while not negatively impacting the yield. One of the most important mitigation measures for agricultural grasslands could be conversion of low yielding cropland, particularly on slopes, to shrub land or grassland, which is also a promising option to decrease soil erosion. In addition, grazing exclusion and reduced grazing intensity can increase SOC sequestration and decrease overall emissions while improving the largely degraded grasslands. For livestock production, where poor quality forage is commonly fed, improving grazing management and diet quality can reduce methane (CH4) emissions by 11% and 5%, on average. Dietary supplements can reduce CH4 emissions further, with lipids (15% reduction) and tannins or saponins (11% reduction) showing the greatest potential. We also suggest the most economically cost-effective mitigation measures, drawing on related work on the construction of marginal abatement cost curves for the sector. تمثل الزراعة ما يقرب من 11 ٪ من انبعاثات غازات الدفيئة الوطنية في الصين. من خلال اعتماد أفضل ممارسات الإدارة الخاصة بالمنطقة، يمكن للمزارعين الصينيين المساهمة في الحد من الانبعاثات مع الحفاظ على الأمن الغذائي لعدد كبير من سكانها (>1300 مليون). تعرض هذه الورقة نتائج تقييم تصاعدي لقياس الإمكانات التقنية لتدابير التخفيف للزراعة الصينية باستخدام التحليل التلوي للبيانات من 240 منشورًا للأراضي الزراعية و 67 منشورًا للأراضي العشبية و 139 منشورًا للثروة الحيوانية، وتقدم السيناريو المرجعي لتحليل تكلفة تدابير التخفيف المحددة. تتمثل خيارات الإدارة ذات إمكانات التخفيف الأكبر للأرز، أو أنظمة المحاصيل القائمة على الأرز في الحراثة الحافظة، والري الخاضع للرقابة ؛ واستبدال اليوريا بكبريتات الأمونيوم، واستخدام مثبطات النيتروجين، واستخدام الأسمدة المخفضة، والزراعة المتكاملة لبط الأرز والسمك، واستخدام الفحم الحيوي. سيؤدي الانخفاض بنسبة 15 ٪ في المتوسط الحالي لاستخدام الأسمدة النيتروجينية الاصطناعية للأرز في الصين، أي 231 كجم نيوتن هكتار-1، إلى انخفاض بنسبة 12 ٪ في انبعاثات أكسيد النيتروز المباشرة للتربة (N2O). يعد التطبيق المشترك للأسمدة الكيميائية والعضوية والحراثة الحافظة واستخدام الفحم الحيوي وتقليل استخدام النيتروجين من التدابير الممكنة التي يمكن أن تقلل من إجمالي انبعاثات غازات الدفيئة من أنظمة زراعة الأراضي المرتفعة. تبلغ مدخلات الأسمدة التقليدية للخضروات الدفيئة أكثر من 2–8 أضعاف الطلب الأمثل على مغذيات المحاصيل. يمكن أن يؤدي الانخفاض بنسبة 20-40 ٪ في استخدام الأسمدة النيتروجينية في محاصيل الخضروات إلى تقليل انبعاثات أكسيد النيتروز بنسبة 32-121 ٪، مع عدم التأثير سلبًا على المحصول. يمكن أن يكون أحد أهم تدابير التخفيف للمراعي الزراعية هو تحويل الأراضي الزراعية منخفضة الغلة، لا سيما على المنحدرات، إلى أراضي شجيرات أو مراعي، وهو أيضًا خيار واعد لتقليل تآكل التربة. بالإضافة إلى ذلك، يمكن أن يؤدي استبعاد الرعي وتقليل كثافة الرعي إلى زيادة عزل مخزون الكربون العضوي في التربة وتقليل الانبعاثات الإجمالية مع تحسين المراعي المتدهورة إلى حد كبير. بالنسبة للإنتاج الحيواني، حيث يتم تغذية الأعلاف ذات الجودة الرديئة بشكل شائع، يمكن أن يؤدي تحسين إدارة الرعي وجودة النظام الغذائي إلى تقليل انبعاثات الميثان (CH4) بنسبة 11 ٪ و 5 ٪ في المتوسط. يمكن أن تقلل المكملات الغذائية من انبعاثات الميثان بشكل أكبر، حيث تظهر الدهون (انخفاض بنسبة 15 ٪) والعفص أو الصابونين (انخفاض بنسبة 11 ٪) أكبر إمكانات. نقترح أيضًا تدابير التخفيف الأكثر فعالية من حيث التكلفة من الناحية الاقتصادية، بالاعتماد على العمل ذي الصلة بشأن بناء منحنيات تكلفة التخفيض الهامشية للقطاع.

Abstract China is a key global region vulnerable to climate change; however, limited studies have focused on the combined impacts of atmospheric CO2 enrichment and warming on crop production in arable land, especially in rice paddies in China. To address this issue, a 4 year open-air field experiment during 2010–2014 was conducted to simulate the impact of climate change on crop production in a rice paddy in southeast of China. Four treatments including the ambient condition (CK), CO2 enrichment (500 ppmv, CE), warming of canopy air (2 °C above the ambient, WA), and the combined CO2 enrichment and warming (CW) were used to investigate the responses of total biomass, crop yield and harvest index. In general, different treatments significantly affected wheat and rice production. Compared to CK, CE significantly increased grain yield of rice by 8%. In contrast, the decreases of 26.2% and 10% in wheat and rice yield were observed under WA. However, there was no significant difference of wheat production between CW and CK, while rice yield and biomass were slightly decreased by a mean of 4.8% and 5.3% over 4 years, indicating the positive effect of CO2 enrichment was unable to compensate for the negative impact of warming. The interannual variations of the responses were also observed in this study. The variation of wheat yields during 4 years was much higher than that of rice yields; however, significant changes in the stability of rice biomass and harvest index were observed under CE and WA. The results indicated both stabilizing and increasing grain yield under climate change are major challenges for agriculture in developing countries.

Abstract Reliable quantification of nitrous oxide emission is a key to assessing efficiency of use and environmental impacts of N fertilizers in crop production. In this study, N2O emission and yield were quantified with a database of 853 field measurements in 104 reported studies and a regression model was fitted to the associated environmental attributes and management practices from China’s croplands. The fitted emission model explained 48% of the variance in N2O emissions as a function of fertilizer rate, crop type, temperature, soil clay content, and the interaction between N rate and fertilizer type. With all other variables fixed, N2O emissions were lower with rice than with legumes and then other upland crops, lower with organic fertilizers than with mineral fertilizers. We used the subset of the dataset for rice - covering a full range of different typical water regimes, and estimated emissions from China’s rice cultivation to be 31.1 Gg N2O-N per year. The fitted yield model explained 35% of the variance in crop yield as a function of fertilizer rate, temperature, crop type, and soil clay content. Finally, the empirical models for N2O emission and crop yield were coupled to explore the optimum N rates (N rate with minimum N2O emission per unit yield) for combinations of crop and fertilizer types. Consequently, the optimum N application rate ranged between 100 kg N ha−1 and 190 kg N ha−1 respectively with organic and mineral fertilizers, and different crop types. This study therefore improved on existing empirical methods to estimate N2O emissions from China’s croplands and suggests how N rate may be optimized for different crops, fertilizers and site conditions.

AbstractThe regulation of soil water retention by biochar amendment has been concerned especially in cropland ecosystem. However, the quantification of biochar's effects on soil hydrological properties and crop water use efficiency (WUE) is still limited, and the factors driving the biochar effect need to be investigated. Based on a database with 681 observations, meta‐analysis and structural equation model (SEM) were employed to reveal how biochar amendment affects water supply capacity and WUE. The results showed that biochar application increased available water content (AWC) and WUE by 26.8% and 4.7% on average, respectively. According to the SEM of AWC (R2 = 0.70–0.96), the increase of soil organic carbon (+36.1%) by biochar application can not only directly improve AWC but also indirectly improve AWC by affecting permanent wilting point (−1.0%) and mean weight diameter (+11.1%). The SEM of WUE (R2 = 0.74) indicated that soil moisture and porosity were increased by 10.8% and 7.0% under biochar amendment, which was the reason why biochar improved WUE. This study emphasized that biochar can improve soil hydrology and crop yield by increasing soil water supply conditions. And a rational rate of biochar is the precondition to obtaining the benefits of soil hydrology, otherwise, the excessive use of biochar may lead to the decline of WUE.

Biochar soil amendment had been increasingly advocated for improving crop productivity and reducing carbon footprint in agriculture worldwide. However, the long-term benefits of biochar application with farming systems had not been thoroughly understood. This study quantified and assessed emergy, energy, and economic benefits of rice and wheat production throughout 6 rotation years following a single biochar amendment in a rice paddy from Southeastern China. Using the data from farm inventory, the quantified emergy indices included grain outputs, unit emergy value, and relative percentage of free renewable resources, environmental loading ratio, emergy yield ratio, and emergy sustainability index (ESI). The results indicated contrasting differences in these emergy values between biochar-amended and unamended production systems over the 6 years. The overall emergy efficiency of rice and wheat productions in biochar-amended system were higher by 11-28 and 15-47%, respectively, than that of unamended one of which the production being highly resource intensive. Moreover, ESI on average was 0.46 for rice and 0.63 for wheat in amended system, compared to 0.35 for rice and 0.39 for wheat in unamended one. Furthermore, over the 6 years following a single application, the ESI values showed considerable variation in the unamended system but consistently increasing in the amended system. Again, the biochar-amended system exerted significantly higher energy and economic return than the unamended one. Nonetheless, there was a tradeoff between rice and wheat in grain yield and net economic gain. Overall, biochar amendment could be a viable measure to improve the resilience of grain production while to reduce resource intensity and environment impacts in paddy soil from China.

AbstractDespite research into the response of ammonia (NH3) volatilization in farmland to various meteorological factors, the potential impact of future climate change on NH3 volatilization is not fully understood. Based on a database consisting of 1063 observations across China, nonlinear NH3 models considering crop type, meteorological, soil and management variables were established via four machine learning methods, including support vector machine, multi‐layer perceptron, gradient boosting machine and random forest (RF). The RF model had the highest R2 of 0.76 and the lowest RMSE of 0.82 kg NH3‐N ha−1, showing the best simulation capability. Results of model importance indicated that NH3 volatilization was mainly controlled by total input of N fertilizer, followed by meteorological factors, human managements and soil characteristics. The NH3 emissions of China's cereal production (paddy rice, wheat and maize) in 2018 was estimated to be 3.3 Mt NH3‐N. By 2050, NH3 volatilization will increase by 23.1−32.0% under different climate change scenarios (Representative Concentration Pathways, RCPs), and climate change will have the greatest impact on NH3 volatilization in the Yangtze river agro‐region of China due to high warming effects. However, the potential increase in NH3 volatilization under future climate change can be mitigated by 26.1−47.5% through various N fertilizer management optimization options.

The ‘4 per mille Soils for Food Security and Climate’ was launched at the COP21 with an aspiration to increase global soil organic matter stocks by 4 per 1000 (or 0.4 %) per year as a compensation for the global emissions of greenhouse gases by anthropogenic sources. This paper surveyed the soil organic carbon (SOC) stock estimates and sequestration potentials from 20 regions in the world (New Zealand, Chile, South Africa, Australia, Tanzania, Indonesia, Kenya, Nigeria, India, China Taiwan, South Korea, China Mainland, United States of America, France, Canada, Belgium, England & Wales, Ireland, Scotland, and Russia). We asked whether the 4 per mille initiative is feasible for the region. The outcomes highlight region specific efforts and scopes for soil carbon sequestration. Reported soil C sequestration rates globally show that under best management practices, 4 per mille or even higher sequestration rates can be accomplished. High C sequestration rates (up to 10 per mille) can be achieved for soils with low initial SOC stock (topsoil less than 30 t C ha− 1), and at the first twenty years after implementation of best management practices. In addition, areas which have reached equilibrium will not be able to further increase their sequestration. We found that most studies on SOC sequestration only consider topsoil (up to 0.3 m depth), as it is considered to be most affected by management techniques. The 4 per mille number was based on a blanket calculation of the whole global soil profile C stock, however the potential to increase SOC is mostly on managed agricultural lands. If we consider 4 per mille in the top 1m of global agricultural soils, SOC sequestration is between 2-3 Gt C year− 1, which effectively offset 20–35% of global anthropogenic greenhouse gas emissions. As a strategy for climate change mitigation, soil carbon sequestration buys time over the next ten to twenty years while other effective sequestration and low carbon technologies become viable. The challenge for cropping farmers is to find disruptive technologies that will further improve soil condition and deliver increased soil carbon. Progress in 4 per mille requires collaboration and communication between scientists, farmers, policy makers, and marketeers.