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

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

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

Ground Cover Rice Production System Affects Soil Water, Nitrogen Dynamics and Crop Growth Differentially with or without Climate Stress

The ground cover rice production system (GCRPS) has been proposed as a potential solution to alleviate seasonal drought and early low-temperature stress in hilly mountainous areas; clarifying its impact on crop growth is crucial to enhance rice productivity in these areas. A two-year (2021-2022) field experiment was conducted in the hilly mountains of southwest China to compare the effects of the traditional flooding paddy (Paddy) and GCRPS under three different nitrogen (N) management practices (N1, zero-N fertilizer; N2, 135 kg N ha-1 as a urea-based fertilizer; and N3, 135 kg N ha-1 with a 3:2 base-topdressing ratio as urea fertilizer for the Paddy or a 1:1 basal application ratio as urea and manure for GCRPS) on soil water storage, soil mineral N content and crop growth parameters, including plant height, tiller numbers, the leaf area index (LAI), aboveground dry matter (DM) dynamics and crop yield. The results showed that there was a significant difference in rainfall between the two growth periods, with 906 mm and 291 mm in 2021 and 2022, respectively. While GCRPS did not significantly affect soil water storage, soil mineral N content, and plant height, it led to a reduction in partial tiller numbers (1.1% to 31.6%), LAI (0.6% to 20.4%), DM (4.4% to 18.8%), and crop yield (7.4% to 22.0%) in 2021 (wet year) compared to the Paddy. However, in 2022 (dry year), GCRPS led to an increase in tiller numbers (13.7% to 115.4%), LAI (17.3% to 81.0%), DM (9.0% to 62.6%), and crop yield (2.9% to 9.2%) compared to the Paddy. Structural equation modeling indicated that GCRPS significantly affected tiller numbers, plant height, LAI, DM, and productive tiller numbers, which indirectly influenced crop yield by significantly affecting tiller numbers and productive tiller numbers in 2022. Overall, the effects of GCRPS on soil water and N dynamics were not significant. In 2021, with high rainfall, no drought, and no early, low-temperature stress, the GCRPS suppressed crop growth and reduced yield, while in 2022, with drought and early low-temperature stress and low rainfall, the GCRPS promoted crop growth and increased yield, with tiller numbers and productive tiller numbers being the key factors affecting crop yield.

Distribution and weathering characteristics of microplastics in paddy soils following long-term mulching: A field study in Southwest China

Agricultural plastic-film residues have been considered as one of the important sources of microplastics in the agroecosystem. However, limited researches were conducted on the accumulation of microplastics in long-term film-mulched paddy soil. This study aims to investigate the distribution and the weathering characteristics of filmy microplastics in a mulched paddy field (non-mulch, four years of mulched, and ten years of continuous mulched soil were investigated) in Southwest China. More than 50 % of the microplastics in the mulched soil were 1-3 mm, whereas the largest percentage of the microplastics in the non-mulched soil was <1 mm (55.3 %). Microplastic compositions in this field mainly consist of polyester (PES) and polyethylene (PE) (82.1 %). The abundance of microplastics increases with the film mulching time, which were 76.2 ± 18.4, 118.6 ± 44.8, and 159.6 ± 23.5 items kg^-1 in soil with non-mulching, four years of mulching, and ten years of continuous mulching, respectively. The filmy microplastics accumulated annually in the plough layer is estimated at 18.1 million items ha^-1. Weathering characteristics of filmy microplastics extracted from paddy soil were characterized using FTIR, SEM-EDS, AFM, and contact angle meter. The vinyl, carbonyl, and hydroxyl indices calculated from FTIR results showed that the degradation degree of microplastics incereased as mulching time rose; compared with commercial PE films, the oxygen-containing functional groups of soil-extracted PE films were increased. This study revealed the status of microplastic pollution in paddy soil with long-term mulching. It provided primary data and a scientific basis for further study on environmental behavior and ecological impacts of microplastics in agricultural soils.

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

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

Degradation characteristics of biodegradable film and its effects on soil nutrients in tillage layer, growth and development of taro and yield formation

This study investigated the degradation characteristics of different biodegradable film and its effects on soil nutrients in tillage layer, growth and development of taro and yield formation. Field experiment with biodegradable films, including poly-(butylene adipate-co-butylene terephthalate) PBAT, (poly-carbon dioxide) PCO2, (poly propylene carbonate) PPC, as well as common mulch film (CK1) and uncovered mulch film (CK2) were conducted on Longxiang taro in 2020 and 2021 respectively. The degradation rate of the three biodegradable films was PBAT > PPC > PCO2. Compared with CK1, the alkali-hydrolyzed N of PBAT at the growth stage and fruiting stage significantly increased in 2020 and 2021, respectively (both, P < 0.05). The average content of available P of PPC at seedling stage was higher than that in PCO2, and CK1 was significantly decreased compared with that in CK2 (all, P < 0.05). The content of soil available K and organic matter in different growth stages of taro in all film mulching treatments were decreased in comparison to CK2. Moreover, compared with CK2, PCO2 biodegradable film significantly increased plant height at seedling and growth stage, stem diameter at growth stage, and leaf area index at fruiting stage (all, P < 0.05). Similarly, the yield of mother and filial bulbs of PPC, PCO2 and PBAT were significantly higher than those of CK2 in 2020 and 2021, respectively (all, P < 0.05). However, no significant differences were found in starch, polysaccharide and protein contents among different treatments. The three biodegradable films, especially PCO2, can significantly affect soil nutrient content, promote plant growth and improve taro yield.

Induced Genetic Variations in Stomatal Density and Size of Rice Strongly Affects Water Use Efficiency and Responses to Drought Stresses

Rice (Oryza sativa L.) is an important food crop relied upon by billions of people worldwide. However, with increasing pressure from climate change and rapid population growth, cultivation is very water-intensive. Therefore, it is critical to produce rice that is high-yielding and genetically more water-use efficient. Here, using the stabilized fast-neutron mutagenized population of Jao Hom Nin (JHN) - a popular purple rice cultivar - we microscopically examined hundreds of flag leaves to identify four stomatal model mutants with either high density (HD) or low density (LD) stomata, and small-sized (SS) or large-sized (LS) stomata. With similar genetic background and uniformity, the stomatal model mutants were used to understand the role of stomatal variants on physiological responses to abiotic stress. Our results show that SS and HD respond better to increasing CO2 concentration and HD has higher stomatal conductance (gs) compared to the other stomatal model mutants, although the effects on gas exchange or overall plant performance were small under greenhouse conditions. In addition, the results of our drought experiments suggest that LD and SS can better adapt to restricted water conditions, and LD showed higher water use efficiency (WUE) and biomass/plant than other stomatal model mutants under long-term restricted water treatment. Finally, our study suggests that reducing stomata density and size may play a promising role for further work on developing a climate-ready rice variety to adapt to drought and heat stress. We propose that low stomata density and small size have high potential as genetic donors for improving WUE in climate-ready rice.

Effect of soil mulching on agricultural greenhouse gas emissions in China: A meta-analysis

Human demand for food has been increasing as population grows around the world. Meanwhile, global temperature has been rising with the increase of greenhouse gas (GHG) emissions. Although soil mulching (SM) is an effective method to increase crop yield because it could conserve soil moisture and temperature, it is also an important factor affecting GHG productions and emissions. At present, research results in terms of the impact of SM on agricultural GHG emissions are still inconsistent. Therefore, a meta-analysis was used to quantitatively analyze the impact of SM on crop yield and GHG emissions in China. Overall, SM significantly enhanced not only crop yield, but also GHG emissions. Compared with no soil mulching (NSM), SM improved crop yield by 21.84%, while increased global warming potential (GWP) by 11.38%. To minimize the negative impact of SM on GHG, for maize and wheat in arid, semi-arid and semi-humid zones, it is recommended to use flat full mulching with grave or straw plus drip irrigation under neutral or weakly alkaline soil with bulk density <1.3g cm^-3. For rice in humid regions, it is advisable to apply SM to minimize GHG emissions by significantly decreasing CH₄ emissions.

Impact of Dietary Protein Content on Soil Bacterial and Fungal Communities in a Rice-Crab Co-culture System

Although co-culture of paddy fields with aquatic animals is lucrative, the ecological impacts of high-protein content entering the agricultural soil via animal pellet feed and feces have not been well studied. Moreover, the effects of dietary protein on soils and soil microbes remain unclear. To elucidate this, we examined soil bacterial and fungal community composition and temporal changes in paddy fields subjected to different protein-content diets via 16S/18S rRNA gene amplicon sequencing analysis with a high-throughput next-generation sequencer. MiSeq sequencing revealed that protein content significantly impacted fungal community structure. High-protein diets reduced bacterial community diversity and relative abundance in both July and October. The phylum-level bacterial taxonomic composition was not affected by diet treatment, while in fungi, a major phylum-level shift was evident. Hierarchically clustered analysis showed that high-protein diets significantly reduced the relative abundance of Brevundimonas in both July and October. Saprotrophic macrofungal diversity was negatively related to dietary protein content. Considering microbial community structure and environmental factors, ca. 15% protein content is appropriate for the rice-crab co-culture system that we studied.

Elevated atmospheric CO2 reduces yield-scaled N2 O fluxes from subtropical rice systems: Six site-years field experiments

Increasing levels of atmospheric CO₂ are expected to enhance crop yields and alter soil greenhouse gas fluxes from rice paddies. While elevated CO₂ ( E CO 2 ) effects on CH₄ emissions from rice paddies have been studied in some detail, little is known how E CO 2 might affect N₂ O fluxes or yield-scaled emissions. Here, we report on a multi-site, multi-year in-situ FACE (free-air CO₂ enrichment) study, aiming to determine N₂ O fluxes and crop yields from Chinese subtropical rice systems as affected by E CO 2 . In this study, we tested various N fertilization and residue addition treatments, with rice being grown under either E CO 2 (+200 μmol/mol) or ambient control. Across the six site-years, rice straw and grain yields under E CO 2 were increased by 9%-40% for treatments fertilized with ≥150 kg N/ha, while seasonal N₂ O emissions were decreased by 23%-73%. Consequently, yield-scaled N₂ O emissions were significantly lower under E CO 2 . For treatments receiving insufficient fertilization (≤125 kg N/ha), however, no significant E CO 2 effects on N₂ O emissions were observed. The mitigating effect of E CO 2 upon N₂ O emissions is closely associated with plant N uptake and a reduction of soil N availability. Nevertheless, increases in yield-scaled N₂ O emissions with increasing N surplus suggests that N surplus is a useful indicator for assessing N₂ O emissions from rice paddies. Our findings indicate that with rising atmospheric CO₂ soil N₂ O emissions from rice paddies will decrease, given that the farmers' N fertilization is usually sufficient for crop growth. The expected decrease in N₂ O emissions was calculated to compensate 24% of the simultaneously observed increase in CH₄ emissions under E CO 2 . This shows that for an agronomic and environmental assessment of E CO 2 effects on rice systems, not only CH₄ emissions, but also N₂ O fluxes and yield-scaled emissions need to be considered for identifying most climate-friendly and economically viable options for future rice production.

Biogeochemical transformation of greenhouse gas emissions from terrestrial to atmospheric environment and potential feedback to climate forcing

Carbon dioxide (CO₂) is mainly universal greenhouse gas associated with climate change. However, beyond CO₂, some other greenhouse gases (GHGs) like methane (CH₄) and nitrous oxide (N₂O), being two notable gases, contribute to global warming. Since 1900, the concentrations of CO₂ and non-CO₂ GHG emissions have been elevating, and due to the effects of the previous industrial revolution which is responsible for climate forcing. Globally, emissions of CO₂, CH₄, and N₂O from agricultural sectors are increasing as around 1% annually. Moreover, deforestation also contributes 12-17% of total global GHGs. Perhaps, the average temperature is likely to increase globally, at least 2 °C by 2100-by mid-century. These circumstances are responsible for climate forcing, which is the source of various human health diseases and environmental risks. From agricultural soils, rhizospheric microbial communities have a significant role in the emissions of greenhouse gases. Every year, microbial communities release approximately 1.5-3 billion tons of carbon into the atmospheric environment. Microbial nitrification, denitrification, and respiration are the essential processes that affect the nitrogen cycle in the terrestrial environment. In the twenty-first century, climate change is the major threat faced by human beings. Climate change adversely influences human health to cause numerous diseases due to their direct association with climate change. This review highlights the different anthropogenic GHG emission sources, the response of microbial communities to climate change, climate forcing potential, and mitigation strategies through different agricultural management approaches and microbial communities.

The Effects of Biodegradable Mulch Film on the Growth, Yield, and Water Use Efficiency of Cotton and Maize in an Arid Region

Plastic residual film pollution in China is severe, and the use of degradable mulch film instead of plastic mulch can effectively alleviate this situation. The substitution of common polyethylene plastic mulch film with biodegradable mulch film in the agricultural production of cotton and maize in an arid region was investigated in the present study. Using bare soil as the control, we compared the effects of common polyethylene plastic film and biodegradable mulch film on crop growth, yield, and water use efficiency (WUE) in maize and cotton. The results indicated that: (1) the biodegradable mulch film in this region remained intact for 60 days after being laid down, significantly degrading after 120 days, and was associated with increased soil temperature, moisture conservation, and degradability in comparison to a bare soil control; (2) Both the biodegradable mulch film and the polyethylene plastic film significantly increased various physiological parameters, such as crop height, stalk diameter, and leaf area; (3) The biodegradable mulch film had a significant effect on crop yield by 69.4–76.2% and 65.2–71.9%, respectively, compared to the bare soil control. (4) Compared to the bare soil control, the biodegradable mulch film effectively increased WUE in the crops by 64.5–73.1%. In summary, biodegradable mulch film had comparable results to the common polyethylene plastic film in increasing crop growth, yield, and WUE. As the biodegradable mulch film causes no residual pollution, it is thus preferable to common plastic mulch film for agricultural applications in arid regions and supports the sustainable development of agroecosystems. Therefore, the use of degradable mulch films in agricultural production is more environmentally friendly and more conducive to the sustainable development of agricultural systems.

Benefits of integrated nutrient management on N2O and NO mitigations in water-saving ground cover rice production systems

To cope with challenges of food security and water scarcity in rice production, water-saving ground cover rice production systems (GCRPSs) are increasingly adopted in China and globally. Reduced soil moisture as well as increased soil aeration and temperature under GCRPSs may promote soil N transformations, and in turn give rise to environmental challenges. These include emissions of the potent greenhouse gas nitrous oxide (N₂O) and atmospheric pollutant nitric oxide (NO). Using conventional flooding rice cultivation as a reference, a three-year field experiment was conducted to investigate the performances of GCRPSs under inorganic (urea) or integrated nutrient management (a combination of synthetic and organic fertilizers), with regards to soil N₂O and NO emissions as well as grain yields. N₂O and NO emissions in GCRPSs exhibited high seasonal and interannual variations along with changes in soil inorganic N content and rainfall. When urea alone was applied, the average N₂O and NO emissions from GCRPSs were 4.11 and 0.14 kg N ha^-1, respectively. These emissions were significantly higher than those of conventional rice cultivation, with 1.47 and 0.052 kg N ha^-1 for N₂O and NO, respectively. When integrated nutrient management was performed for GCRPSs, N₂O and NO emissions were reduced by approximately 77% and 50%, respectively, i.e., the emission magnitude comparable with N-trace gas losses from conventional rice cultivation. Moreover, GCRPSs with integrated nutrient management resulted in optimal grain yields, and thus, the yield-scaled N₂O + NO emissions were the lowest compared to other treatments. Averaged over 3 years, the direct emission factors of N₂O and NO for GCRPSs with urea alone were 2.58% and 0.064%, respectively. Those for GCRPSs with integrated nutrient management were 0.48% and 0.016%, respectively. The results of this study suggest that GCRPS with integrated nutrient management is an eco-friendly strategy for optimizing crop yields while mitigating N₂O and NO emissions.

The environmental costs and benefits of high-yield farming

How we manage farming and food systems to meet rising demand is pivotal to the future of biodiversity. Extensive field data suggest impacts on wild populations would be greatly reduced through boosting yields on existing farmland so as to spare remaining natural habitats. High-yield farming raises other concerns because expressed per unit area it can generate high levels of externalities such as greenhouse gas (GHG) emissions and nutrient losses. However, such metrics underestimate the overall impacts of lower-yield systems, so here we develop a framework that instead compares externality and land costs per unit production. Applying this to diverse datasets describing the externalities of four major farm sectors reveals that, rather than involving trade-offs, the externality and land costs of alternative production systems can co-vary positively: per unit production, land-efficient systems often produce lower externalities. For GHG emissions these associations become more strongly positive once forgone sequestration is included. Our conclusions are limited: remarkably few studies report externalities alongside yields; many important externalities and farming systems are inadequately measured; and realising the environmental benefits of high-yield systems typically requires additional measures to limit farmland expansion. Yet our results nevertheless suggest that trade-offs among key cost metrics are not as ubiquitous as sometimes perceived.