Greenhouse gas emissions and global warming potential of traditional and diversified tropical rice rotation systems

Effects of Ratoon Rice Cropping Patterns on Greenhouse Gas Emissions and Yield in Double-Season Rice Regions

The ratoon rice cropping pattern is an alternative to the double-season rice cropping pattern in central China due to its comparable annual yield and relatively lower cost and labor requirements. However, the impact of the ratoon rice cropping pattern on greenhouse gas (GHG) emissions and yields in the double-season rice region requires further investigation. Here, we compared two cropping patterns, fallow-double season rice (DR) and fallow-ratoon rice (RR), by using two early-season rice varieties (ZJZ17, LY287) and two late-season rice varieties (WY103, TY390) for DR, and two ratoon rice varieties (YLY911, LY6326) for RR. The six varieties constituted four treatments, including DR1 (ZJZ17 + WY103), DR2 (LY287 + TY390), RR1 (YLY911), and RR2 (LY6326). The experimental results showed that conversion from DR to RR cropping pattern significantly altered the GHG emissions, global warming potential (GWP), and GWP per unit yield (yield-scaled GWP). Compared with DR, the RR cropping pattern significantly increased cumulative methane (CH4), nitrous oxide (N2O), and carbon dioxide (CO2) emissions by 65.73%, 30.56%, and 47.13%, respectively, in the first cropping season. Conversely, in the second cropping season, the RR cropping pattern effectively reduced cumulative CH4, N2O, and CO2 emissions by 79.86%, 27.18%, and 30.31%, respectively. RR led to significantly lower annual cumulative CH4 emissions, but no significant difference in cumulative annual N2O and CO2 emissions compared with DR. In total, the RR cropping pattern reduced the annual GWP by 7.38% and the annual yield-scaled GWP by 2.48% when compared to the DR cropping pattern. Rice variety also showed certain effects on the yields and GHG emissions in different RR cropping patterns. Compared with RR1, RR2 significantly increased annual yield while decreasing annual GWP and annual yield-scaled GWP. In conclusion, the LY6326 RR cropping pattern may be a highly promising strategy to simultaneously reduce GWP and maintain high grain yield in double-season rice regions in central China.

Comparison of crop productivity, economic benefit and environmental footprints among diversified multi-cropping systems in South China

Diversified multi-cropping system with high productivity and low environmental costs is crucial for the development of sustainable agriculture in different regions. However, the information on this practice has still been limited in the South China. This study compared different diversified multi-cropping systems including peanut-rice-fallow (P-R-F), peanut-rice-ryegrass (P-R-R), soybean-rice-ryegrass (S-R-R), feed corn-rice-milk vetch (FC-R-M), sweet corn-rice-milk vetch (SC-R-M) and zucchini -rice-milk vetch (Z-R-M), with the conventional double-rice system (CK). A newly proposed agricultural environmental footprint index (EFI) framework was introduced to quantify the comprehensive environmental costs of different systems. Results indicated that the annual productivities of P-R-R and FC-R-M rotation systems significantly increased by 39.91 % and 25.06 %, respectively, compared to the CK. The economic benefits of P-R-R and FC-R-M were 53.71 % and 16.67 % higher than the CK, respectively, with significant differences. The EFIs based on unit farmland area, crop productivity and economic benefit of the P-R-R and FC-R-M systems were 17.07 %-40.68 % lower than the CK, respectively, showing the lower environmental costs. Therefore, the P-R-R and FC-R-M were recommended as alternatives of double-rice cropping in the South China. In addition, the results indicated that the fertilization and irrigation practices were the key points for improving the rotation systems. This study provided valuable information for the transition of rice-based cropping system in South China. It was also a reference for the development of sustainable agriculture in the world's subtropical agricultural system.

Importance of biochar as a key amendment to convert rice paddy into carbon negative

Biochar being made up of recalcitrant carbon (C) compounds is considered a negative emission technology (NET) due to its indirect removal of atmospheric carbon dioxide (CO₂). However, there is no clear report about how biochar remains a NET when organic amendment application in rice paddy results in a huge emission of greenhouse gases (GHG) particularly, methane (CH₄). To evaluate the net impact of biochar application on the net global warming potential (GWP) in rice paddy, no organic amendment (control), fresh manure, compost, and biochar treatments were selected during the whole investigation period. Compared to compost, biochar application decreased annual CH₄ and N₂O emissions by 55 and 31 %, respectively. In comparison to the control, biochar application increased CH₄ emission by 163 % but decreased N₂O emission by 19 %. Soil organic carbon (SOC) stock would annually deplete by 2.2 Mg C ha^-1 under control; however, biochar application could increase the SOC stock by 18.1 Mg C ha^-1 which was 63 and 33 % higher than fresh and compost treatments, respectively. As a result, the control had a net GWP of 10 Mg CO₂-eq ha^-1 however, this impact was increased with fresh manure and compost application by around 319 and 159 %, respectively. Interestingly, biochar application converted rice paddy into a C sink having a net GWP of -0.104 to -0.191 Mg CO₂-eq ha^-1. Since there was a comparable difference in grain yield among organic amendments, greenhouse gas intensity (GHGI) which is the net GWP per grain yield was significantly high in compost application of approximately 3.1 Mg CO₂-eq Mg^-1 grain being 127 % higher than control. However, the biochar application had a -0.02 Mg CO₂-eq Mg^-1 grain which was 1.4 Mg CO₂-eq Mg^-1 grain lower than the control. Conclusively, biochar application could be a considerable option in maintaining soil quality and productivity without contributing any GHG emissions and their associated impacts.

Oxygen micro-nanobubbles for mitigating eutrophication induced sediment pollution in freshwater bodies

Sediment hypoxia is a growing problem and has negative ecological impacts on the aquatic ecosystem. Hypoxia can disturb the biodiversity and biogeochemical cycles of both phosphorus (P) and nitrogen (N) in water columns and sediments. Anthropogenic eutrophication and internal nutrient release from lakebed sediment accelerate hypoxia to form a dead zone. Thus, sediment hypoxia mitigation is necessary for ecological restoration and sustainable development. Conventional aeration practices to control sediment hypoxia, are not effective due to high cost, sediment disturbance and less sustainability. Owing to high solubility and stability, micro-nanobubbles (MNBs) offer several advantages over conventional water and wastewater treatment practices. Clay loaded oxygen micro-nanobubbles (OMNBs) can be delivered into deep water sediment by gravity and settling. Nanobubble technology provides a promising route for cost-effective oxygen delivery in large natural water systems. OMNBs also have the immense potential to manipulate biochemical pathways and microbial processes for remediating sediment pollution in natural waters. This review article aims to analyze recent trends employing OMNBs loaded materials to mitigate sediment hypoxia and subsequent pollution. The first part of the review highlights various minerals/materials used for the delivery of OMNBs into benthic sediments of freshwater bodies. Release of OMNBs at hypoxic sediment water interphase (SWI) can provide significant dissolved oxygen (DO) to remediate hypoxia induced sediment pollution Second part of the manuscript unveils the impacts of OMNBs on sediment pollutants (e.g., methylmercury, arsenic, and greenhouse gases) remediation and microbial processes for improved biogeochemical cycles. The review article will facilitate environmental engineers and ecologists to control sediment pollution along with ecological restoration.

Artificial intelligence-based decision support systems in smart agriculture: Bibliometric analysis for operational insights and future directions

As the world population is expected to touch 9.73 billion by 2050, according to the Food and Agriculture Organization (FAO), the demand for agricultural needs is increasing proportionately. Smart Agriculture is replacing conventional farming systems, employing advanced technologies such as the Internet of Things (IoT), Artificial Intelligence (AI), and Machine Learning (ML) to ensure higher productivity and precise agriculture management to overcome food demand. In recent years, there has been an increased interest in researchers within Smart Agriculture. Previous literature reviews have also conducted similar bibliometric analyses; however, there is a lack of research in Operations Research (OR) insights into Smart Agriculture. This paper conducts a Bibliometric Analysis of past research work in OR knowledge which has been done over the last two decades in Agriculture 4.0, to understand the trends and the gaps. Biblioshiny, an advanced data mining tool, was used in conducting bibliometric analysis on a total number of 1,305 articles collected from the Scopus database between the years 2000–2022. Researchers and decision makers will be able to visualize how newer advanced OR theories are being applied and how they can contribute toward some research gaps highlighted in this review paper. While governments and policymakers will benefit through understanding how Unmanned Aerial Vehicles (UAV) and robotic units are being used in farms to optimize resource allocation. Nations that have arid climate conditions would be informed how satellite imagery and mapping can assist them in detecting newer irrigation lands to assist their scarce agriculture resources.

Methane emission, methanogenic and methanotrophic communities during rice-growing seasons differ in diversified rice rotation systems

Appropriate crop rotation in rice field is an important measure to maintain soil fertility and rice productivity. However, the effects of different rice rotation systems on methane (CH₄) emission and the underlying mechanisms, as well as rice grain yields have not been well assessed. Here, a 2-year field study involving three rice rotation systems (Wh-PR: wheat-flooded rice rotation, Ra-PR: rapeseed-flooded rice rotation, Ra-UR: rapeseed-aerobic rice rotation) was conducted. CH₄ emissions, methanogenic and methanotrophic communities and rice grain yields were measured during rice growing seasons to determine which rice rotation pattern can reduce CH₄ emissions and improve rice grain yields. The average cumulative CH₄ emission was 136.19 kg C ha^-1 in Ra-PR system, which was significantly higher than that in Wh-PR and Ra-UR systems by 60.6 % and 14.6-fold, respectively. These results were mainly attributed to the low soil dissolved organic carbon in Wh-PR system and the well aerated soil condition in Ra-UR system, as compared with Ra-PR system. Rice grain yields exhibited no significant differences among the three rotation systems in 2019 and 2020. The abundances of methanogens in Ra-PR system were obviously higher than those in Wh-PR and Ra-UR systems. While the abundances of methanotrophs were comparable between Ra-PR and Wh-PR systems, which exhibited significantly lower abundances than that in Ra-UR system. CH₄ fluxes showed markedly positive relations to the abundances of methanogens, while exhibited no relationship with the abundances of methanotrophs. Both methanogenic and methanotrophic community compositions differed considerably in Wh-PR and Ra-UR systems in comparison with Ra-PR system. Specifically, the relative low abundances of Methanothrix and Type I methanotrophs occurred in Wh-PR and Ra-UR systems, whereas Methanosarcina, Methanocella, Methanomassiliicoccus and type II methanotrophs (Methylocystis and Methylosinus) were found in higher relative abundances in Wh-PR and Ra-UR systems. Overall, changing the preceding upland crop types or introducing aerobic rice to substitute flooded rice in rice-based rotation systems could diminish CH₄ emissions, mainly by regulating soil properties and eventually changing soil methanogenic and methanotrophic communities.

Effects of combined applications of straw with industrial and agricultural wastes on greenhouse gases emissions, temperature sensitivity, and rice yield in a subtropical paddy field

The incorporation of post-harvest crop straw and application of industrial and agricultural wastes to paddy soils increase rice crop yields and soil fertility. However, the impacts of combined applications of straw and waste products on greenhouse gas (GHG) emissions and global warming potential (GWP) of paddy soils are unclear. Therefore, we conducted a field experiment in subtropical rice in China to test the effects of applications of straw, straw+biochar, straw+shell slag, straw+gypsum slag, straw+silicon, and straw+steel slag on rice yields, GWP, and greenhouse gas emission intensity (GHGI). The results showed that, compared to the control, cumulative emissions of carbon dioxide (CO₂) from paddy soils were 15.2, 16.9, and 36.6 % lower following application of straw+steel slag, straw+silicon, and straw+gypsum, respectively, and cumulative emissions of methane (CH₄) were 5.0 and 62.1 % lower following application of straw+steel slag and straw+gypsum, respectively. Meanwhile, relative to the addition of straw alone, application of straw+steel slag and straw+gypsum reduced GHG emissions largely due to reductions in CO₂ emissions, further declining the GWP of CO₂ and GHGI. In addition, temperature sensitivity (Q₁₀) of CO₂ emissions was highest following application of straw+silicon and lowest following application of straw+gypsum. There were no treatment effects on mean dissolved porewater concentrations of CO₂, CH₄, or nitrous oxide (N₂O) and soil emissions of CO₂ were negatively correlated with mean dissolved concentrations of CO₂, CH₄, and N₂O. Rice yields were reduced following application of straw+gypsum and unaffected by the other treatments. Thus, relative to the addition of straw alone or control, we suggest the combined application of straw+steel slag may improve the sustainability of paddy rice production, because it reduces GWP, while maintaining yields.

Transcriptomic and metabolomic reveals silicon enhances adaptation of rice under dry cultivation by improving flavonoid biosynthesis, osmoregulation, and photosynthesis

Dry cultivation is a new rice crop mode used to alleviate water shortage and develop water-saving agriculture. There is obvious genetic difference compared with drought-tolerant rice. Silicon (Si) plays an important role in plant adaptation to adverse environmental conditions and can significantly improve the drought tolerance and yield of rice. However, the regulatory mechanism via which Si provides plant tolerance or adaptation under dry cultivation is not well understood. The present study investigated the changes in plant growth, photosynthetic gas exchange, and oxidative stress of the rice cultivar "Suijing 18" under dry cultivation. Si improved photosynthetic performance and antioxidant enzyme activity and subsequently reduced lipid peroxidation of rice seedlings, promoted LAI and promoted leaf growth under dry cultivation. Further, transcriptomics combined with quasi-targeted metabolomics detected 1416 and 520 differentially expressed genes (DEGs), 38 and 41 differentially accumulated metabolites (DAMs) in the rice leaves and roots, respectively. Among them, 13 DEGs were involved in flavonoid biosynthesis, promoting the accumulation of flavonoids, anthocyanins, and flavonols in the roots and leaves of rice under dry cultivation. Meanwhile, 14 DEGs were involved in photosynthesis, promoting photosystem I and photosystem II responses, increasing the abundance of metabolites in leaves. On the other hand, 24 DAMs were identified involved in osmoregulatory processes, significantly increasing amino acids and carbohydrates and their derivatives in roots. These results provide new insight into the role of Si in alleviating to adverse environmental, Si enhanced the accumulation of flavonoids and osmoregulatory metabolites, thereby alleviating drought effect on the roots. On the other hand, improving dehydration resistance of leaves, guaranteeing normal photosynthesis and downward transport of organic matter. In conclusion, Si promoted the coordinated action between the above-ground and below-ground plant parts, improved the root/shoot ratio (R/S) of rice and increased the sugar content and enhancing rice adaptability under dry cultivation conditions. The establishment of the system for increasing the yield of rice under dry cultivation provides theoretical and technical support thereby promoting the rapid development of rice in Northeast China, and ensuring national food security.

Conversion from double-season rice to ratoon rice paddy fields reduces carbon footprint and enhances net ecosystem economic benefit

Ratoon rice (RR) system is an alternative to the double-season rice (DR) system in central China due to its high annual yield and relatively lower cost and labor requirement. However, the effect of conversion from DR to RR on the carbon footprint (CF) and net ecosystem economic benefit (NEEB) remains largely unknown. Here, we elucidated the effect by using two early-season rice varieties (ZJZ17, LY287) and two late-season rice varieties (WY103, TY390) for the DR system, and two RR varieties (YLY911, LY6326) for the RR system. The six varieties constituted four cropping systems, including DR1 (ZJZ17 + WY103), DR2 (LY287 + TY390), RR1 (YLY911) and RR2 (LY6326). The two-year experiment demonstrated that RR had 27.37% lower annual CF than DR, which could be attributed to the significantly lower annual CF (by 87.27%) of ratoon crop in RR relative to that of the late-season rice in DR. Direct greenhouse gas (GHG) emissions contributed the most to annual CF in both systems, accounting for 43.28% and 35.39% in DR and RR, respectively. Furthermore, conversion from DR to RR system significantly increased annual NEEB by 30.95%. This increase could be attributed to the 20.25% higher annual grain yield of main crop in RR relative to early-season rice in DR, and 75.32% and 87.27% lower annual costs for agricultural inputs and CF of ratoon crop than late-season rice in DR, respectively. Rice variety also showed certain effects on the yields and GHG emissions in different RR systems. Compared with RR1, RR2 significantly increased annual yield and annual NEEB, while decreased annual CF and annual yield-scaled CF (CF_y). These findings suggest that the conversion of the DR system to LY6326 RR system may be a highly promising strategy to simultaneously reduce CF, promote NEEB and maintain high grain yield in central China.

Comprehensive quantification of global cropland ammonia emissions and potential abatement

Ammonia (NH₃) emissions mostly from agriculture result in air pollution and degrade human health. However, a full picture of soil NH₃ emissions and associated abatement in cropping systems are not well understood. Here we present a thorough analysis of cropland NH₃ emissions, discuss mitigation potential and assess associated abatement costs. Global cropland NH₃ emissions account for 26% of total soil nitrogen losses, and are estimated as 22.8-31.2 Tg N yr^-1 during 1996-2013 with the increase rate of 1.6% yr^-1. Our results also show that, with no increase in nitrogen fertilizer, climate change can contribute to an additional 10% increase in cropland NH₃ emissions in 2100 compared to the 2010 baseline. Instead, our scenario analysis show, cropland NH₃ emissions will decline by 26% from 2010 to 2100 given a 0.5% yr^-1 decrease in N fertilizer (with current technology and agricultural management level), considering the facts stronger control policies are expected to occur worldwide including Western Europe, the United States of America and China. The most ambitious management (with all known mitigation practices) can reduce cropland NH₃ emissions by up (71%, 17.6 Tg N yr^-1) at an abatement cost of US$524 billion. Our findings indicate that cropland NH₃ emissions can be mitigated through adoption of appropriate human management practices with considerable economic costs, providing a critical reference for the future NH₃ abatement strategies.

The overlap of suitable tea plant habitat with Asian elephant (Elephus maximus) distribution in southwestern China and its potential impact on species conservation and local economy

The expansion of land being used for cash crop cultivation has threatened wildlife in recent decades. Tea has become the dominant cash crop in southwestern China. Unfortunately, tea plantations may threaten Asian elephant (Elephus maximus) populations via habitat loss and fragmentation. Identifying areas of suitable habitat for tea plant cultivation, and where this habitat overlaps with Asian elephant distribution, is vital for planning land use, managing nature reserves, shaping policy, and maintaining local economies. Here, we assess the potential impact of tea plantations on Asian elephants in southwestern Yunnan province, China. We used MaxEnt modeling with bioclimatic and environmental variables to identify suitable habitat for tea plant cultivation under the current climate scenario, and then overlapped this habitat with 9 known Asian elephant distribution areas (G1-G9) to determine "threatened areas." Our results showed that (1) annual precipitation (48.1% contribution), temperature constancy (29 % contribution), and slope (8.7 % contribution) were key in determining suitable habitat for tea plants; (2) the cumulative area of suitable habitat for tea plants was 13,784.88 km², mainly distributed in Menghai (3934.53 km²), Lancang (3198.67 km²), and Jinghong (2657.74 km²); (3) the distribution area of elephants was 943.75 km², and these areas overlapped with suitable tea plant habitat primarily located in G4 (379.40 km²), G3 (251.18), and G7 (168.03 km²); and (4) threatened areas in G1 and G7 were predominately located along the periphery of current nature reserves. Win-win solutions that work for elephant conservation and economic development include rescoping nature reserve boundaries, strengthening management on the periphery of nature reserves, establishing ecological corridors and new nature reserves within regions where elephants are currently distributed, planting alternative cash crops, and financial subsidies to farmers. This study improves understanding of human-elephant coexistence, and will assist in guiding land use policy for the future conservation outcomes seeking to promote responsible and profitable cash crop farming and elephant conservation.

Setting-up of different water managements as mitigation strategy of the environmental impact of paddy rice

Northern Italy represents the most important rice-growing district in Europe. In this area, rice is the main annual crop and the main revenues source for farmers. However, Italian climatic condition led to a traditional cultivation characterized by continuous flooding, causing emissions of methane into the atmosphere due to the organic matter fermentation in anaerobic conditions, and, consequently, a high environmental impact. The water conditions of paddy fields also affect heavy metals uptake by rice plants. In this context, this study focuses on the evaluation of environmental impact and of heavy metal content in paddy rice, and it may represent an important step in mitigating the environmental impact of rice production. In detail, this study quantifies the environmental benefits related to the adoption of an alternative water management characterized by an additional aeration period during stem elongation. To this purpose, field trials were carried out and the Life Cycle Assessment (LCA) approach was applied with a cradle-to-farm gate perspective. The potential environmental impact of the production of two rice varieties (Carnaroli and Caravaggio) was analysed in terms of 12 different impact categories and dehulled rice grain were analysed for arsenic and cadmium content. Alternative flooding decreases CH₄ emissions in all cases evaluated (from 15% to 52%), resulting in a reduction in the climate change impact of rice cultivation (from 12% to 32%). Furthermore, the alternative water management does not influence grain yield and it reduces all the other environmental impact categories in 2 out of 4 cases. Regarding the heavy metals contents, the arsenic content in the grain decreases in all alternative scenarios, whereas the cadmium content increases, while remaining well below the legal limits.

Bioprospecting plant growth-promoting rhizobacteria from rice genotypes and their influence on growth under aerobic conditions

The bacteria that colonize plant roots and enhance plant growth by various mechanisms are known as plant growth-promoting rhizobacteria (PGPR). The functions of rhizobacteria stand substantially unexplored and detailed insights into the aerobic rice ecosystem are yet to be examined. In this study, we have isolated rhizobacteria from rice varieties grown under aerobic conditions. Seed germination test showed that strain Ekn 03 was significantly effective in stimulating germination, enhancing shoot and root length, and increasing dry matter accumulation in treated rice plants as compared to the uninoculated plants. Under greenhouse conditions, strain Ekn 03 treated rice varieties showed an overall increase in plant height by 7.63%, dry matter accumulation by 16.23%, and total chlorophyll content by 76.47%. Soil acetylene reduction assay (ARA) (4.17 nmole ethylene/g soil/h) and in-planta ARA (4.2 × 10^-2  nmole ethylene/mg fresh weight of plant/h) was significantly higher in Ekn 03 treated rice variety PB 1509 under aerobic conditions. Other rice varieties showed comparable performance on inoculation with strain Ekn 03. The endophytic and rhizospheric population of antibiotic tagged Ekn 03 was higher in the roots of PB 1509 (1.02 × 10⁴  cfu/g and 5.8 × 10⁵ cfu/g soil, respectively) compared to other rice varieties. 16S rDNA sequence analysis revealed that strain Ekn 03 was having 100% similarity with Pseudomonas protegens. This study suggests that strain Ekn 03 can be used as a microbial inoculant in rice plants under aerobic system of cultivation. This is the first report on the application of P. protegens as PGPR in rice.

Effects of nitrogen-enriched biochar on rice growth and yield, iron dynamics, and soil carbon storage and emissions: A tool to improve sustainable rice cultivation

Biochar is often applied to paddy soils as a soil improver, as it retains nutrients and increases C sequestration; as such, it is a tool in the move towards C-neutral agriculture. Nitrogen (N) fertilizers have been excessively applied to rice paddies, particularly in small farms in China, because N is the major limiting factor for rice production. In paddy soils, dynamic changes in iron (Fe) continuously affect soil emissions of methane (CH₄) and carbon dioxide (CO₂); however, the links between Fe dynamics and greenhouse gas emissions, dissolved organic carbon (DOC), and rice yields following application of biochar remain unclear. The aims of this study were to examine the effects of two rates of nitrogen (N)-enriched biochar (4 and 8 t ha^-1 y^-1) on paddy soil C emissions and storage, rice yields, and Fe dynamics in subtropical early and late rice growing seasons. Field application of N-enriched biochar at 4 and 8 t ha^-1 increased C emissions in early and late rice, whereas application at 4 t ha^-1 significantly increased rice yields. The results of a culture experiment and a field experiment showed that the application of N-enriched biochar increased soil Fe²⁺concentration. There were positive correlations between Fe²⁺concentrations and soil CO₂, CH₄, and total C emissions, and with soil DOC concentrations. On the other way around, these correlations were negative for soil Fe³⁺concentrations. In the soil culture experiment, under the exclusion of plant growth, N-enriched biochar reduced cumulative soil emissions of CH₄ and CO₂. We conclude that moderate inputs of N-rich biochar (4 t ha^-1) increase rice crop yield and biomass, and soil DOC concentrations, while moderating soil cumulative C emissions, in part, by the impacts of biochar on soil Fe dynamics. We suggest that water management strategies, such as dry-wet cycles, should be employed in rice cultivation to increase Fe²⁺ oxidation for the inhibition of soil CH₄ and CO₂ production. Overall, we showed that application of 4 t ha^-1 of N-enriched biochar may represent a potential tool to improve sustainable food production and security, while minimizing negative environmental impacts.

Paddy-upland rotation with Chinese milk vetch incorporation reduced the global warming potential and greenhouse gas emissions intensity of double rice cropping system

It is a common practice to maintain soil fertility based on the paddy-upland rotation with green manure in the subtropical region of China. However, rare studies are known about greenhouse gas (GHG) emissions from the paddy-upland rotation with green manure incorporation. Therefore, we conducted a field experiment of two years to compared with the effect of two kinds of green manure (CV: Chinese milk vetch and OR: Oilseed rape), and two kinds of cropping system (DR: double rice system and PR: paddy-upland rotation) on greenhouse gases emissions. We have found that the annual accumulation of CH₄ of Chinese milk vetch-rice-sweet potato || soybean was significantly reduced by 32.95%∼63.22% compared with other treatments, mainly because Chinese milk vetch reduced the abundance of methanogens by reducing soil C/N ratio. Meanwhile increasing soil permeability resulting from paddy-upland rotation also reduced soil CH₄ emission. However, The annual accumulation of N₂O of Chinese milk vetch-rice-sweet potato || soybean was increased by 17.39%∼870.11% compared with other treatments, mainly attributed to paddy-upland rotation decreased soil pH and nosZ abundance and increased nirK and nirS, thus enhancing N₂O emission, meanwhile the Chinese milk vetch incorporation and its interaction with the paddy-upland rotation has greatly enhanced the contents of NO₃^--N and abundance of ammonia-oxidizing archaea (AOA). The area-scaled global warming potential (GWP) and the biomass-scaled greenhouse gas emissions intensity (GHGI) of Chinese milk vetch-rice-sweet potato || soybean was reduced by 19.01%∼50.69% and 5.38%∼35.77% respectively. Thereby, the Chinese milk vetch-rice-sweet potato || soybean cropping system was suitable for agricultural sustainable development.

Soil Nitrous Oxide Emissions by Atmospheric Nitrogen Deposition over Global Agricultural Systems

Agricultural soil is the main source of nitrous oxide (N₂O) emissions which contribute to global warming and stratospheric ozone depletion. In recent decades, atmospheric nitrogen (N) deposition has increased dramatically as an important agricultural soil N input, while its effect on soil N₂O emissions in the current and future climate change remains unknown. Here, we conducted a thorough analysis of the effect of N deposition and climate change on soil N₂O emissions as well as their trends. Soil N₂O emissions induced by N deposition accounted for 25% of global cropland soil N₂O emissions. Global soil N₂O emissions over croplands increased by 2% yr^-1 during 1996-2013, of which N deposition could explain 15% of the increase. The emission factor of N deposition was ∼7 times that of N fertilizer plus manure (∼1%) through a more direct way, since N deposition including nitrate (NO₃^-) and ammonium (NH₄⁺) could be directly used for nitrification and denitrification. By 2100, N deposition will increase by 80% and cropland soil N₂O emissions will increase by 241% under the RCP8.5 scenario in comparison with the 2010 baseline. These results suggest that, under the background of increasing global N deposition, it is essential to consider its effects on soil N₂O emissions in climatic change studies.

Strong mitigation of greenhouse gas emission impact via aerobic short pre-digestion of green manure amended soils during rice cropping

To increase soil carbon (C) stock, cover crop cultivation during the fallow season and its biomass incorporation as green manure (GM) is strongly suggested in mono-rice paddy. On the other hand, biomass application can highly increase greenhouse gas (GHG) emission, in particular methane (CH₄) during irrigated cropping season. Aerobic short pre-digestion of biomass applied soils was very effective to suppress CH₄ emission. However, its effect on other GHG (CO₂ and N₂O) emissions was not clear. To assess the integrated influence of aerobic short pre-digestion of green manured soils on global warming impact, cover crop biomass as GM was amended with different time interval before flooding (0-30 days) and aerobically decomposed under upland condition. Aerobic short pre-digestion over 10 days significantly decreased seasonal CH₄ flux, but did not affect N₂O emission. As aerobic pre-digestion days became longer, net ecosystem C balance (NECB) which implies the difference between C input and output was slightly increased, but not statistically different. The net primary productivity of rice plant as a C input source was not significantly differentiated by aerobic short pre-digestion. As a C output source, the respired C loss that was composed with CO₂-C and CH₄-C emission was not considerably discriminated among 0-30 days of aerobic short pre-digestion. As a consequence, due to big reduction of CH₄ emission, aerobic short pre-digestion significantly decreased net GWP which means integration of seasonal CH₄ and N₂O fluxes and NECB as CO₂ equivalent. In conclusion, aerobic short pre-digestion of biomass applied soil could be a sustainable management practice to decrease GHG emission impact without SOC stock change in temperate rice paddy field.

Evaluation of resource and energy utilization, environmental and economic benefits of rice water-saving irrigation technologies in a rice-wheat rotation system

Currently, numerous challenges such as excessive irrigation water consumption, labor shortage, lower economic and environmental benefits pose serious threats to rice cultivation systems. Therefore, more water- and labor-efficient irrigation technologies are needed in rice production for minimal environmental hazards and greater economic benefits. After the screening experiment of water-saving cultivation technologies and cultivars, a two-year field experiment was conducted to further explore the effects of efficient water-saving technologies and rice cultivars on the comprehensive benefits, global warming potential (GWP), grain yield, economic benefits, water productivity, nitrogen partial factor productivity, radiation, accumulated temperature and energy use efficiency (EUE) of a rice-wheat rotation system. Conventional flooding irrigation (F), intermittent irrigation (IR), transplanting rainfed (TR) and rice dry cultivation (D) were implemented with two rice cultivars, including Hanyou73 (HY) and Huanghuazhan (HH). After rice harvest, a winter wheat cultivar (Huamai 2566) was planted with traditional methods. The system of rice dry cultivation and wheat rotation had higher comprehensive benefits, which were attributed to greater water productivity, economic benefits and EUE and lower GWP, especially in the rice growing season. D treatment enhanced the comprehensive and economic benefits by 2.5% and 26.8%, 1.6% and 11.3%, 3.3% and 0.6%, and reduced the GWP by 3.4%, 56.7% and 30.2% compared with F, IR and TR treatments in the rotation system, respectively. During the rice season, D treatment significantly (P < 0.05) increased the economic benefits, water productivity and EUE, but slight decreased the grain yield than other treatments. Overall, rice dry cultivation (especially with the HY cultivar) can achieve higher comprehensive benefits in rice growing season as well as in the whole rotation system.

Tuning of the Amount of Se in Rice (Oryza sativa) Grain by Varying the Nature of the Irrigation Method: Development of an ICP-MS Analytical Protocol, Validation and Application to 26 Different Rice Genotypes

The amount of specific trace elements like selenium (Se) may be of health concern for humans if contained in too high (or low) quantities in staple foods like rice. Among the attempts aimed to optimize the Se concentration in rice, only few studies have been focused on the use of irrigation methods other than continuous flooding. Since intermittent irriguous methods, like sprinkler and saturation, have found to be effective in modifying the bioaccumulation of arsenic and cadmium in rice kernels, the main goal of this study is to measure the amount of the total Se contained in grains of 26 rice genotypes cultivated for two consecutive agrarian vintages in the same open field and with the same water, but differently irrigated with continuous flooding, sprinkler or saturation. To do this, an original and validated ICP-MS method has been developed. The validation parameters accounted for a high sensitivity and accuracy. Sprinkler irrigation is able to reduce in the average of 90% the amount of total Se in kernels in comparison to values measured in rice irrigated with continuous flooding. In conclusion, different irrigation techniques and rice genotypes seem to be valuable tools in order to allow in the future the customized modulation of the Se concentration in rice grain according to the needs of the various populations.

Agriculture, dairy and fishery farming practices and greenhouse gas emission footprint: a strategic appraisal for mitigation

Rising global population would force farmers to amplify food production substantially in upcoming 3-4 decades. The easiest way to increase grain production is through expanding cropping area by clearing uncultivated land. This is attained by permitting deadly loss of carbon (C) stocks, jeopardizing ecosystem biodiversity and deteriorating environmental quality. We aim to propose key agronomical tactics, livestock management strategy and advance approaches for aquaculture to increase productivity and simultaneously reduce the environmental impacts of farming sector. For this, we considered three major sectors of farming, i.e. agriculture, fishery and dairy. We collected literatures stating approaches or technologies that could reduce GHG emission from these sectors. Thereafter, we synthesized strategies or options that are more feasible and accessible for inclusion in farm sector to reduce GHG emission. Having comprehensively reviewed several publications, we propose potential strategies to reduce GHG emission. Agronomic practices like crop diversification, reducing summer fallow, soil organic carbon sequestration, tillage and crop residue management and inclusion of N₂-fixing pulses in crop rotations are some of those. Livestock management through changing animals' diets, optimal use of the gas produced from manures, frequent and complete manure removal from animal housing and aquaculture management strategies to improve fish health and improve feed conversion efficiency could reduce their GHG emission footprint too. Adapting of effective and economic practices GHG emission footprint reduction potential of farming sector could make farming sector a C neutral enterprise. To overcome the ecological, technological and institutional barriers, policy on trade, tax, grazing practice and GHG pricing should be implemented properly.

Earthworms offset straw-induced increase of greenhouse gas emission in upland rice production

Increasing water scarcity and rapid socio-economic development are driving farmers in Asia to transform traditionally flooded rice cropping systems into non-flooded crop production. The management of earthworms in non-flooded rice fields appears to be a promising strategy to support residue recycling and mitigate greenhouse gas (GHG) emissions triggered by residue amendment. We conducted a field experiment on non-flooded rainfed rice fields, with and without residue amendment. In-situ mesocosms were inoculated with endogeic earthworms (Metaphire sp.), with either low (ET1: 150 individuals m^-2), or high density (ET2: 450 individuals m^-2), and a control (ET0: no earthworms). We measured GHG emissions (methane (CH₄); nitrous oxide (N₂O); carbon dioxide (CO₂)) twice a week during the cropping season with static chambers. Effects of earthworms on yield and root growth were additionally assessed. Earthworms offset the enormous increase of CH₄ emissions induced by straw amendment (from 4.6 ± 5 to 75.3 ± 46 kg CH₄-C ha^-1 in ET0). Earthworm activity significantly reduced CH₄ release, particularly at ET2, by more than one-third (to 22 ± 15 kg CH₄-C ha^-1). In contrast, earthworm inoculation did not affect N₂O emission. Straw amendment more than doubled the global warming potential (GWP). Earthworms reduced GWP by 39% at low (ET1) and 55% at high densities (ET2). Earthworm activity reduced root mass density under conditions of straw amendment but did not affect yield. Earthworms can significantly reduce detrimental effects of rice crop residue amendment on GHG release under upland rice production. Organic carbon (C) might be preserved in earthworm casts and thereby limit C availability for CH₄ production. At the same time, earthworm activity might increase methanotrophic CH₄ consumption, due to improved soil aeration or less root exudates. Consequently, earthworms have a strong potential for regulating ecosystem functions related to rice straw decomposition, nutrient allocation and thus GHG reduction.

Long-term effect of rice-based cropping systems on pools of soil organic carbon in farmer's field in hilly agroecosystem of Manipur, India

A comprehensive study on various pools of soil organic carbon (SOC) under different rice-based cropping systems is necessary for predicting their effect on soil quality through carbon build-up in soil and their impact on global climate change. The present investigation was undertaken to study the long-term effect of six different rice-based cropping systems (continuously followed by farmers > 10 years) on various SOC pools viz., total organic carbon (TOC), oxidizable organic carbon (C_oc) and its different fractions [C_frac1 (very labile), C_frac2 (labile), C_frac3 (less labile) and C_frac4 (non-labile)], soil microbial biomass carbon (SMBC) and lability index (LI) and SOC stock at the farmer's field of Kakching district under hilly ecosystems of Manipur, India. In every cropping system, all the fractions of C_oc were significantly decreased with increasing soil depth. Among all the fractions, C_frac4 (non-labile) constituted the largest percentage of TOC for both surface (0-20 cm) and sub-surface (20-40 cm) soil varying from 47.95-58.45% and 55.76-64.83% with average values of 51.87 and 59.73% respectively. Results also revealed that the C_frac1 (very labile) of C_oc constituted highest (42.79%) percentage of C_oc and that of C_fract4 constituted highest percentage (55.80%) of TOC. In both soil depths, rice-pea cropping system recorded highest TOC, C_oc and SMBC followed by rice-French bean and rice-potato. In surface soil, the lowest TOC, C_oc and SMBC were recorded in rice-mustard which was statistically at par with rice-cabbage. The SOC stock of both soil layers was also recorded highest in rice-pea. The highest LI of surface soil was recorded in rice-potato which was statistically equal with rice-pea and rice-French bean. Significant correlations among different pools/fractions of C and with available nutrients indicate their importance in improving soil quality. Long-term combination of rice with the leguminous crops and/or potato enhanced C_oc, TOC, SMBC, LI and active pools (C_frac1 + C_frac2) of rapid turnover rate that may influence the quality and productivity of soil. Long-term cultivation of rice-French bean with high passive C along with good active C and LI is proved to be a good cropping system for sustaining soil and environment by enhancing quality and C reserve of degraded soils of hilly agroecosystem.

Dynamics and underlying mechanisms of N2O and NO emissions in response to a transient land-use conversion of Masson pine forest to tea field

Nowadays, there has been a rapid expansion of tea field converted from forestry for pursuing higher economic benefits. However, few researches focus on the effects of transient land-use conversion from Masson pine forest to artificial tea fields on soil N₂O and NO emissions and the underlying mechanisms. A parallel field experiment was conducted from Masson pine forest and a newly converted tea plantation from Masson pine forest from 2013 to 2017 in subtropical central China. Masson pine forest conversion to tea field dramatically increased soil N₂O and NO emissions (up to 4.00 ± 0.43 and 1.93 ± 0.45 kg N ha^-1 yr^-1, respectively) in the first year possibly due to enhanced soil organic N mineralization. With the extension of tea planting age, N₂O and NO emissions showed an upward trend (ranged from 1.19 to 5.28, and 0.15 to 1.78 kg N ha^-1 yr^-1, respectively) influenced by fertilization and soil organic matter accumulation. The direct emission factors for N₂O and NO in the newly converted tea fields were the largest in the first year (2.64 and 1.07%, respectively) after land-use conversion, and higher than the default value recommended by IPCC. The NO/N₂O ratio was mainly lower than 1 in the fertilized tea field, and soil N₂O and NO emission peaks mainly occurred in tea-growing season (wet season) with higher soil moisture and NH₄⁺-N concentrations, and dominated by amoA-containing bacteria (AOB), suggesting nitrifier-denitrification could be the dominant process involved in soil nitrogenous gases emissions in tea field. These results can be summarized as dramatically increased soil N₂O and NO emissions during the transient land-use conversion from Masson pine forest to tea field were possibly due to the substantial net soil organic N mineralization and the enhanced abundance of nitrification functional genes (AOB).

Effect of moisture gradient on rice yields and greenhouse gas emissions from rice paddies

Fluxes of methane (CH₄) and nitrous oxide (N₂O) from two rice varieties, Huayou 14 and Hanyou 8, were monitored using closed chamber/gas chromatography method. Huayou 14 is a commonly grown variety of rice whereas Hanyou 8 is a water-saving and drought-resistant rice (WDR) variety. Low soil volumetric water content (VWC) existed in the treatments on the slope (W5 < W4 < W3 < W2). On the slope, rice yields of Hanyou 8 decreased by 12-39%, and Huayou 14 by 11-46% as compared to the plots on the flat. The total compatible solutes in Hanyou 8 had a greater variational range than Huayou 14. Compared to W1, CH₄ emissions from W2-W5 decreased by 58-86% in Hanyou 8 and 38-86% in Huayou 14, whereas those of N₂O increased by 26-121% in Hanyou 8 and 49-189% in Huayou 14 across both two seasons, which was mainly because the VWC varied in W2-W5 treatment. Under the treatments in the slope (W2, W3, W4, and W5), the global warming potential (GWP) was dominated by N₂O emissions, which accounted for 69-90% of the GWP. Hanyou 8 had greater tolerance for water stress than Huayou 14 did, as evident from the smaller reductions in rice yield and greater variational range of total compatible solutes content. Water stress could reduce CH₄ emissions but decrease N₂O emissions for both rice varieties. This results suggest that planting WDR varieties under water shortage irrigation (such as W4, W5) will be able to maintain rice yields and reduce the GWP with less water.

Engineering meiotic recombination pathways in rice

In the last 15 years, outstanding progress has been made in understanding the function of meiotic genes in the model dicot and monocot plants Arabidopsis and rice (Oryza sativa L.), respectively. This knowledge allowed to modulate meiotic recombination in Arabidopsis and, more recently, in rice. For instance, the overall frequency of crossovers (COs) has been stimulated 2.3- and 3.2-fold through the inactivation of the rice FANCM and RECQ4 DNA helicases, respectively, two genes involved in the repair of DNA double-strand breaks (DSBs) as noncrossovers (NCOs) of the Class II crossover pathway. Differently, the programmed induction of DSBs and COs at desired sites is currently explored by guiding the SPO11-1 topoisomerase-like transesterase, initiating meiotic recombination in all eukaryotes, to specific target regions of the rice genome. Furthermore, the inactivation of 3 meiosis-specific genes, namely PAIR1, OsREC8 and OsOSD1, in the Mitosis instead of Meiosis (MiMe) mutant turned rice meiosis into mitosis, thereby abolishing recombination and achieving the first component of apomixis, apomeiosis. The successful translation of Arabidopsis results into a crop further allowed the implementation of two breakthrough strategies that triggered parthenogenesis from the MiMe unreduced clonal egg cell and completed the second component of diplosporous apomixis. Here, we review the most recent advances in and future prospects of the manipulation of meiotic recombination in rice and potentially other major crops, all essential for global food security.

Management-induced greenhouse gases emission mitigation in global rice production

Mitigating greenhouse gases (GHGs) emissions from rice paddy (Oryza sativa L.) and balancing the trade-offs between reducing emission and sustaining food security have raised global concerns. A global meta-analysis of rice experimental data was conducted to assess changes in emissions of GHGs (CH₄ and N₂O) and global warming potential (GWP) in response to improvements through 12 field management practices. The results indicated that changes in GWP were mainly attributed to CH₄ emission even though N₂O emission was significantly affected by conversion of field management practices. Specifically, GWP per unit rice plant area (area-scaled) was significantly increased by 20.1%, 66.2%, and 84.5% with nitrogen (N) fertilizer input, manuring, and residue retention (P < 0.05), along with significant increments in area-scaled CH₄ emission under the above management practices by 8.9%, 60.4%, and 91.8%, respectively (P < 0.05). Due to the significant increase in rice yield, a decreasing trend for GWP per unit rice yield (yield-scaled) was observed with N fertilizer input. In addition, CH₄ and GWP decreased significantly at both area- and yield-scale under non-flooding irrigation but with a reduction in rice yield by 3.3% (P < 0.05). Improvement in rice variety significantly enhanced crop yield by 15.3% while reducing area-scaled GWP by 27.7% (P < 0.05). Furthermore, other management practices, such as application of herbicides, biochar, and amendments (non-fertilizer materials) reduced yield-scaled GWP while increasing rice yield. Thus, changes in field management practices have the potential to balance the trade-offs between high yield and low emission of GHGs. However, in-depth studies are needed to determine the interactions between field management practices and site-specific soil/climate conditions.

Evaluating the Performance of Rice Genotypes for Improving Yield and Adaptability Under Direct Seeded Aerobic Cultivation Conditions

With the changing climatic conditions and reducing labor-water availability, the potential contribution of aerobic rice varieties and cultivation system to develop a sustainable rice based agri-food system has never been more important than today. Keeping in mind the goal of identifying high-yielding aerobic rice varieties for wider adaptation, a set of aerobic rice breeding lines were developed and evaluated for grain yield, plant height, and days to 50% flowering in 23 experiments conducted across different location in Philippines, India, Bangladesh, Nepal, and Lao-PDR between 2014 and 2017 in both wet and dry seasons. The heritability for grain yield ranged from 0.52 to 0.90. The season-wise two-stage analysis indicated significant genotype x location interaction for yield under aerobic conditions in both wet and dry seasons. The genotype × season × location interaction for yield was non-significant in both seasons indicating that across seasons the genotypes at each location did not show variability in the grain yield performance. Mean grain yield of the studied genotypes across different locations/seasons ranged from 2,085 to 6,433 Kg ha^-1. The best-fit model for yield stability with low AIC value (542.6) was AMMI(1) model. The identified stable genotypes; IR 92521-143-2-2-1, IR 97048-10-1-1-3, IR 91326-7-13-1-1, IR 91326-20-2-1-4, and IR 91328-43-6-2-1 may serve as novel breeding material for varietal development under aerobic system of rice cultivation. High yield and stable performance of promising breeding lines may be due to presence of the earlier identified QTLs including grain yield under drought, grain yield under aerobic conditions, nutrient uptake, anaerobic germination, adaptability under direct seeded conditions, and tolerance to biotic stress resistance such as qDTY _2.1 , qDTY _3.1 , qDTY _12.1 , qNR _5.1 , AG _9.1 , qEVV _9.1 , qRHD _1.1 , qRHD _5.1, qRHD _8.1 qEMM _1.1 , qGY _6.1 , BPH3, BPH17, GM4, xa4, Xa21, Pita, and Pita2. The frequency of xa4 gene was highest followed by qAG _9.1, GM4, qDTY _3.1 , qDTY _2.1 , qGY _6.1, and qDTY _12.1.

Producing more grain yield of rice with less ammonia volatilization and greenhouse gases emission using slow/controlled-release urea

Ammonia (NH₃) volatilization and greenhouse gas (GHG) emission from rice (Oryza sativa L.) fields contaminate the atmospheric environment and lead to global warming. Field trials (2013-2015) were conducted to estimate the influences of different types of fertilization practices on grain yield, NH₃ volatilization, and methane (CH₄) and nitrous oxide (N₂O) emissions in a double rice cropping system in Central China. Results showed that grain yields of rice were improved significantly by using slow/controlled-release urea (S/C-RU). Compared with farmers' fertilizer practice (FFP) treatment, average annual grain yield with application of polymer-coated urea (CRU), nitrapyrin-treated urea (CP), and urea with effective microorganism (EM) treatments was increased by 18.0%, 16.2%, and 15.4%, respectively. However, the effects on NH₃ volatilization and CH₄ and N₂O emissions differed in diverse S/C-RU. Compared with that of the FFP treatment, the annual NH₃ volatilization, CH₄ emission, and N₂O emissions of the CRU treatment were decreased by 64.8%, 19.7%, and 35.2%, respectively; the annual CH₄ and N₂O emissions of the CP treatment were reduced by 33.7% and 40.3%, respectively, while the NH₃ volatilization was increased by 18.5%; the annual NH₃ and N₂O emissions of the EM treatment were reduced by 6.3% and 28.7%, while the CH₄ emission was improved by 4.3%. Overall, CP showed the best emission reduction with a decrement of 34.3% in global warming potential (GWP) and 44.4% in the greenhouse gas intensity (GHGI), followed by CRU treatment with a decrement of 21.1% in GWP and 31.7% in GHGI, compared with that of the FFP treatment. Hence, it is suggested that polymer-coated urea can be a feasible way of mitigating NH₃ volatilization and CH₄ and N₂O emission from rice fields while maintaining or increasing the grain yield in Chinese, the double rice cropping system.

Carbon budget and greenhouse gas balance during the initial years after rice paddy conversion to vegetable cultivation

Rice paddy conversion to vegetable production is a common agricultural practice driven by economic benefits and shifting diets. However, little is known on the initial effects of this land-use conversion on net ecosystem carbon budget (NECB) and greenhouse gas (GHG) balance. Annual NECB and emissions of CH₄ and N₂O were measured from a native double rice cropping system (Rice) and a vegetable field recently converted from rice paddy (Veg) under no nitrogen (N) fertilization (Rice-N⁰ and Veg-N⁰) and conventional N fertilization (Rice-N⁺ and Veg-N⁺) during the initial four years upon conversion in subtropical China. Land-use conversion from rice to vegetable cultivation led to substantial C losses (2.6 to 4.5 Mg C ha^-1 yr^-1), resulting from strongly reduced C input by 44-52% and increased soil organic matter mineralization by 46-59% relative to Rice. The magnitude of C losses from Veg was highest in the first year upon conversion, and showed a decreasing trend over time. N fertilization shifted rice paddy from a slight C source in Rice-N⁰ (-1.0 Mg C ha^-1 yr^-1) to a significant C sink in Rice-N⁺ (1.1 Mg C ha^-1 yr^-1) and alleviated the impact of land-use conversion on C loss via increased C input from higher crop productivity. Land-use conversion greatly increased the global warming potential (GWP) from Veg by 116-395% relative to Rice in the first year, primarily due to increased C losses and N₂O emission outweighing the decreased CH₄ emission. However, the GWP did not show obvious difference between Rice and Veg in the following years. N fertilization and land-use conversion interactively increased GWP in the first year via increased N₂O production. Concluding, NECB and GHG emissions in the first year after conversion are crucial and should be considered when evaluating the environmental consequences of land-use conversion.

Decrease in the annual emissions of CH4 and N2O following the initial land management change from rice to vegetable production

In recent years, rice paddies have been increasingly converted to vegetable production resulting from economic benefits and changes in demand of diets, potentially altering soil greenhouse gas (GHG) balance. Here, we implemented a parallel field experiment to simultaneously quantify the differences in emissions of CH₄ and N₂O among rice paddy (RP) and conventional vegetable field (CV) and greenhouse vegetable field (GV), both of which have been recently converted from rice paddy in subtropical China over a full year. The results revealed that CH₄ emission was reduced dramatically by nearly 100% following the initial land management change from rice to vegetable production, with annual emissions of 720.9, 0.9, and 0.2 kg CH₄-C ha^-1 for RP, CV, and GV, respectively. This conversion however substantially increased N₂O emissions, resulting in the transition from a minor sink of N₂O in RP (-0.1 kg N ha^-1 yr^-1) to considerable N₂O sources in CV (31.8 kg N ha^-1 yr^-1) and GV (52.2 kg N ha^-1 yr^-1). Furthermore, annual N₂O emission from GV significantly exceeded that from CV due to lower soil pH and higher soil temperature facilitating N₂O production in GV relative to CV. Land management change significantly decreased the annual total emissions of CH₄ and N₂O from CV and GV by 19-51% as compared to RP, attributing to the reduced CH₄ emissions outweighing the increased N₂O emissions in CV and GV. These results indicate that expansion of vegetable production at the expense of rice paddies for higher economic benefits also helps mitigate the total emissions of CH₄ and N₂O.

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.

Modeling of methane formation in gravity sewer system: the impact of microorganism and hydraulic condition

Sewer system is an important source of methane formation and emission. Although some models were developed to predict methane production in sewers, the impact of microorganism amount was indicated indirectly. Here, seven laboratory scale sewers with varied wall-shear stresses were established. The biofilm thickness, microorganism amount, DO distribution, microorganism community in the biofilms and methane production in the sewers were measured. Based on experimental data, an empirical model was developed to directly describe the relationship between methane production, microorganism amount and wall-shear stress. The results showed that DO concentration decreased significantly along the biofilm depth under varied wall-shear stress, and the DO reduction rate was positively related to the intensity of wall-shear stress. The dominant archaea species in mature biofilms were similar whereas the proportions showed remarkable differences. The abundance of Methanospirillum in biofilms cultured at 2.0 Pa wall-shear stress was 53.08% more than that at 1.29 Pa. The maximum methane production rate, 2.04 mg/L wastewater day, was obtained when the wall-shear stress kept at 1.45 Pa, which was 1.2-fold higher than the minimum in sewer at 0.5 Pa. The R² value of the established model was 0.95, the difference between the measurement and simulation was in the rage of 1.5–13.0%.

Responses of CH4 and N2O fluxes to land-use conversion and fertilization in a typical red soil region of southern China

Land-use conversion and fertilization have been widely reported as important management practices affecting CH₄ and N₂O fluxes; however, few long-term in situ measurements are available after land-use conversion from rice paddies to upland cultivation, especially those including the initial stages after conversion. A 3-year field experiment was conducted in rice paddies and a newly converted citrus orchard to measure CH₄ and N₂O fluxes in response to land-use conversion and fertilization in a red soil region of southern China. Annual CH₄ and N₂O emissions averaged 303.9 kg C ha^-1 and 3.8 kg N ha^-1, respectively, for the rice paddies over three cultivation years. Although annual N₂O emissions increased two- to threefold after the conversion of rice paddies to citrus orchard, the substantial reduction in CH₄ emissions and even shift into a sink for atmospheric CH₄ led to significantly lower CO₂-eq emissions of CH₄ and N₂O in the citrus orchard compared to the rice paddies. Moreover, distinct CH₄ emissions were observed during the initial stages and sustained for several weeks after conversion. Our results indicated that the conversion of rice paddies to citrus orchards in this region for higher economic benefits may also lead to lower aggregate CH₄ and N₂O emissions.

Ecological determinants of health: food and environment on human health

Human health and diseases are determined by many complex factors. Health threats from the human-animal-ecosystems interface (HAEI) and zoonotic diseases (zoonoses) impose an increasing risk continuously to public health, from those emerging pathogens transmitted through contact with animals, food, water and contaminated environments. Immense challenges forced on the ecological perspectives on food and the eco-environments, including aquaculture, agriculture and the entire food systems. Impacts of food and eco-environments on human health will be examined amongst the importance of human interventions for intended purposes in lowering the adverse effects on the biodiversity. The complexity of relevant conditions defined as factors contributing to the ecological determinants of health will be illuminated from different perspectives based on concepts, citations, examples and models, in conjunction with harmful consequential effects of human-induced disturbances to our environments and food systems, together with the burdens from ecosystem disruption, environmental hazards and loss of ecosystem functions. The eco-health literacy should be further promoting under the "One Health" vision, with "One World" concept under Ecological Public Health Model for sustaining our environments and the planet earth for all beings, which is coincidentally echoing Confucian's theory for the environmental ethics of ecological harmony.

Conversion from rice to vegetable production increases N2O emission via increased soil organic matter mineralization

The conversion from rice to vegetable production widely occurs in China. However, the effects of this conversion on N₂O emission and the underlying mechanisms are not well understood. In the present study, 12 rice paddies (R) were selected and half of them converted to vegetable fields (V) with the following treatments: rice paddies without N-fertilizer (R-CK), rice paddies with conventional N-fertilizer (R-CN), converted vegetable fields without N-fertilizer (V-CK), and converted vegetable fields with conventional N-fertilizer (V-CN) in a randomized block design with 3 replicates. N₂O emissions were measured with static chambers from December 2012 to December 2015. Within each V-CN plot, a root exclusion subplot was established to measure soil heterotrophic respiration (CO₂ effluxes), a proxy for soil organic matter mineralization. Conversion of rice paddies to vegetable production dramatically increased N₂O emissions. The three-year cumulative N₂O emissions were 0.59, 1.90, 55.50 and 160.14kg N ha^-1 for R-CK, R-CN, V-CK and V-CN, respectively. The annual N₂O emissions from vegetable fields ranged between 5.99 and 113.45kg N ha^-1yr^-1, with substantially higher emissions in the first year. N₂O fluxes from V-CN were significantly and positively related to CO₂ fluxes and inorganic N concentrations. The linear relationship between natural logarithms of N₂O and CO₂ fluxes was stronger and the regression coefficient higher in the first year, showing the dependence of N₂O on soil organic matter mineralization. These results suggest that soil organic matter and N mineralization contributes significantly to N₂O emission following conversion of rice paddies to vegetable production.

Effects of screenhouse cultivation and organic materials incorporation on global warming potential in rice fields

Global rice production will be increasingly challenged by providing healthy food for a growing population at minimal environmental cost. In this study, a 2-year field experiment was conducted to investigate the effects of a novel rice cultivation mode (screenhouse cultivation, SHC) and organic material (OM) incorporation (wheat straw and wheat straw-based biogas residue) on methane (CH₄) and nitrous oxide (N₂O) emissions and rice yields. In addition, the environmental factors and soil properties were also determined. Relative to the traditional open-field cultivation (OFC), SHC decreased the CH₄ and N₂O emissions by 6.58-18.73 and 2.51-21.35%, respectively, and the global warming potential (GWP) was reduced by 6.49-18.65%. This trend was mainly because of lower soil temperature and higher soil redox potential in SHC. Although the rice grain yield for SHC were reduced by 2.51-4.98% compared to the OFC, the CH₄ emissions and GWP per unit of grain yield (yield-scaled CH₄ emissions and GWP) under SHC were declined. Compared to use of inorganic fertilizer only (IN), combining inorganic fertilizer with wheat straw (WS) or wheat straw-based biogas residue (BR) improved rice grain yield by 2.12-4.10 and 4.68-5.89%, respectively. However, OM incorporation enhanced CH₄ emissions and GWP, leading to higher yield-scaled CH₄ emissions and GWP in WS treatment. Due to rice yield that is relatively high, there was no obvious effect of BR treatment on them. These findings suggest that apparent environmental benefit can be realized by applying SHC and fermenting straw aerobically before its incorporation.

Improving rice production sustainability by reducing water demand and greenhouse gas emissions with biodegradable films

In China, rice production is facing unprecedented challenges, including the increasing demand, looming water crisis and on-going climate change. Thus, producing more rice at lower environmental cost is required for future development, i.e., the use of less water and the production of fewer greenhouse gas (GHG) per unit of rice. Ground cover rice production systems (GCRPSs) could potentially address these concerns, although no studies have systematically and simultaneously evaluated the benefits of GCRPS regarding yields and considering water use and GHG emissions. This study reports the results of a 2-year study comparing conventional paddy and various GCRPS practices. Relative to conventional paddy, GCRPSs had greater rice yields and nitrogen use efficiencies (8.5% and 70%, respectively), required less irrigation (−64%) and resulted in less total CH₄ and N₂O emissions (−54%). On average, annual emission factors of N₂O were 1.67% and 2.00% for conventional paddy and GCRPS, respectively. A cost-benefit analysis considering yields, GHG emissions, water demand and labor and mulching costs indicated GCRPSs are an environmentally and economically profitable technology. Furthermore, substituting the polyethylene film with a biodegradable film resulted in comparable benefits of yield and climate. Overall, GCRPSs, particularly with biodegradable films, provide a promising solution for farmers to secure or even increase yields while reducing the environmental footprint.

Effects of land use conversion and fertilization on CH4 and N2O fluxes from typical hilly red soil

Land use conversion and fertilization have been widely reported to be important managements affecting the exchanges of greenhouse gases between soil and atmosphere. For comprehensive assessment of methane (CH₄) and nitrous oxide (N₂O) fluxes from hilly red soil induced by land use conversion and fertilization, a 14-month continuous field measurement was conducted on the newly converted citrus orchard plots with fertilization (OF) and without fertilization (ONF) and the conventional paddy plots with fertilization (PF) and without fertilization (PNF). Our results showed that land use conversion from paddy to orchard reduced the CH₄ fluxes at the expense of increasing the N₂O fluxes. Furthermore, fertilization significantly decreased the CH₄ fluxes from paddy soils in the second stage after conversion, but it failed to affect the CH₄ fluxes from orchard soils, whereas fertilizer applied to orchard and paddy increased soil N₂O emissions by 68 and 113.9 %, respectively. Thus, cumulative CH₄ emissions from the OF were 100 % lower, and N₂O emissions were 421 % higher than those from the PF. Although cumulative N₂O emissions were stimulated in the newly converted orchard, the strong reduction of CH₄ led to lower global warming potentials (GWPs) as compared to the paddy. Besides, fertilization in orchard increased GWPs but decreased GWPs of paddy soils. In addition, measurement of soil moisture, temperature, dissolved carbon contents (DOCs), and ammonia (NH₄⁺-N) and nitrate (NO₃^--N) contents indicated a significant variation in soil properties and contributed to variations in soil CH₄ and N₂O fluxes. Results of this study suggest that land use conversion from paddy to orchard would benefit for reconciling greenhouse gas mitigation and citrus orchard cultivation would be a better agricultural system in the hilly red soils in terms of greenhouse gas emission. Moreover, selected fertilizer rate applied to paddy would lead to lower GWPs of CH₄ and N₂O. Nevertheless, more field measurements from newly converted orchard are highly needed to gain an insight into national and global accounting of CH₄ and N₂O emissions.

Greenhouse gas emissions and reactive nitrogen releases during the life-cycles of staple food production in China and their mitigation potential

Life-cycle analysis of staple food (rice, flour and corn-based fodder) production and assessments of the associated greenhouse gas (GHG) and reactive nitrogen (Nr) releases, from environmental and economic perspectives, help to develop effective mitigation options. However, such evaluations have rarely been executed in China. We evaluated the GHG and Nr releases per kilogram of staple food production (carbon and Nr footprints) and per unit of net economic benefit (CO2-NEB and Nr-NEB), and explored their mitigation potential. Carbon footprints of food production in China were obviously higher than those in some developed countries. There was a high spatial variation in the footprints, primarily attributable to differences in synthetic N use (or CH4 emissions) per unit of food production. Provincial carbon footprints had a significant linear relationship with Nr footprints, attributed to large contribution of N fertilizer use to both GHG and Nr releases. Synthetic N fertilizer applications and CH4 emissions dominated the carbon footprints, while NH3 volatilization and N leaching were the main contributors to the Nr footprints. About 564 (95% uncertainty range: 404-701) TgCO2eqGHG and 10 (7.4-12.4) Tg Nr-N were released every year during 2001-2010 from staple food production. This caused the total damage costs of 325 (70-555) billion ¥, equivalent to nearly 1.44% of the Gross Domestic Product of China. Moreover, the combined damage costs and economic input costs, accounted for 66%-80% of the gross economic benefit generated from food production. A reduction of 92.7TgCO2eqyr(-1) and 2.2TgNr-Nyr(-1) could be achieved by reducing synthetic N inputs by 20%, increasing grain yields by 5% and implementing off-season application of straw and mid-season drainage practices for rice cultivation. In order to realize these scenarios, an ecological compensation scheme should be established to incentivize farmers to gradually adopt knowledge-based managements.