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Rice paddies are a major source of methane emission. To meet the food demand of the growing population and to cope with global warming, reducing greenhouse gases and enhancing yield are critical. Here, we demonstrate for the first time that a novel loss-of-function rice allele, gs3, mitigates methane emission from methanogens by allocating more photosynthates to the grain and less to the root, and increases yield by enlarging grain size and weight.

Abstract Oil palm (OP) plantations are gradually replacing tropical rainforest in Malaysia, one of the largest palm oil producers globally. Conversion of lands to OP plantations has been associated with compositional shifts of the microbial community, with consequences on the greenhouse gas (GHG) emissions. While the impact of the change in land use has recently been investigated for microorganisms involved in N2O emission, the response of the aerobic methanotrophs to OP agriculture remains to be determined. Here, we monitored the bacterial community composition, focusing on the aerobic methanotrophs, in OP agricultural soils since 2012, 2006, and 1993, as well as in a tropical rainforest, in 2019 and 2020. High-affinity methane uptake was confirmed, showing significantly lower rates in the OP plantations than in the tropical rainforest, but values increased with continuous OP agriculture. The bacterial, including the methanotrophic community composition, was modified with ongoing OP agriculture. The methanotrophic community composition was predominantly composed of unclassified methanotrophs, with the canonical (Methylocystis) and putative methanotrophs thought to catalyze high-affinity methane oxidation present at higher relative abundance in the oldest OP plantation. Results suggest that the methanotrophic community was relatively more stable within each site, exhibiting less temporal variations than the total bacterial community. Uncharacteristically, a 16S rRNA gene-based co-occurrence network analysis revealed a more complex and connected community in the OP agricultural soil, which may influence the resilience of the bacterial community to disturbances. Overall, we provide a first insight into the ecology and role of the aerobic methanotrophs as a methane sink in OP agricultural soils.

A large volume of slag is generated as a by-product during steel manufacturing. In order to ensure environmental and economic sustainability, it is imperative to find innovative solutions for the e...

With the increase in iron/steel production, the higher volume of by-products (slag) generated necessitates its efficient recycling. Because the Linz-Donawitz (LD) slag is rich in silicon (Si) and other fertilizer components, we aim to evaluate the impact of the LD slag amendment on soil quality (by measuring soil physicochemical and biological properties), plant nutrient uptake, and strengthens correlations between nutrient uptake and soil bacterial communities. We used 16 S rRNA illumine sequencing to study soil bacterial community and APIZYM assay to study soil enzymes involved in C, N, and P cycling. The LD slag was applied at 2 Mg ha−1 to Japonica and Indica rice cultivated under flooded conditions. The LD slag amendment significantly improved soil pH, plant photosynthesis, soil nutrient availability, and the crop yield, irrespective of cultivars. It significantly increased N, P, and Si uptake of rice straw. The slag amendment enhanced soil microbial biomass, soil enzyme activities and enriched certain bacterial taxa featuring copiotrophic lifestyles and having the potential role for ecosystem services provided to the benefit of the plant. The study evidenced that the short-term LD slag amendment in rice cropping systems is useful to improve soil physicochemical and biological status, and the crop yield.

The use of salt- or macro-sized NPK fertilizers is typically associated with low nutrient use efficiency and water eutrophication. Nanotechnology can overcome such drawbacks, but its practical application on a large scale is limited by (i) high costs and difficult scale-up of nanoparticle synthesis, (ii) questionable advantages over traditional methods, and (iii) health hazards related to nanomaterial introduction in the food stream and the environment. Here, we report on a novel biocompatible and multifunctional P nanofertilizer obtained by self-assembling natural or synthetic humic substances and hydroxyapatite nanoparticles using a simple and straightforward dipping process, exploiting the interaction between the polyphenolic groups of humic substances and the surface of nanohydroxyapatite. Pot tests using the as-prepared materials were performed on Zea mays as a model crop, and the results were compared to those obtained using commercial fused superphosphate and bare nanohydroxyapatites. A significant improvement, in terms of early plant growth, corn productivity, rhizosphere bacteria, and the resistance to NaCl-induced abiotic stresses, was achieved using hydroxyapatite nanoparticles assembled with humic substances. These effects were ascribed to the synergistic co-release of phosphate ions and humic substances, which are two types of plant-beneficial agents for crop nutrition and stimulation, respectively. The release patterns were proven to be tunable with the amount of humic substances adsorbed on the nanoparticles, inducing competition between humic-substance-driven phosphorous dissolution and block of water contact. Such positive effects on plant growth in association with its intrinsic biocompatibility, simple synthesis, and multifunctionality qualify this novel nanofertilizer as a promising material for large-scale use in the agronomic field.

Blast furnace slag (BFS), a byproduct of iron-producing process, has been applied as silicate fertilizer in rice paddy. Silicate fertilizer contains lime and silicate as main components and iron and manganese as electron acceptors. This amendment improves soil productivity and mitigates methane (CH

Rice is the main staple food for more than half of the world's population. Yet, rice cultivation is subjected to criticism because of its important role in methane (CH4) emissions. Although several agronomic practices such as controlled irrigation and conservation tillage have been widely adopted to mitigate CH4 emissions from rice cultivation, the benefits gained by these practices are highly dependent on site-specific soil and climate conditions, and often offset by yield reduction. The use of plant growth regulating compounds having the potential to increase the crop yield and mitigate CH4 emissions may be an innovative approach to sustainable agriculture. Ethylene (C2H4), a plant growth regulator is known to have a strong inhibitory effect on methanogenesis. However, due to gaseous form and low water solubility, C2H4 has not been used to suppress methanogenesis in paddy fields. To develop C2H4 as a prospective soil amendment for reducing methane (CH4) emissions, ethephon (2-Chloroethylphosphonic acid), a precursor of C2H4 was tested. We found that ethephon reduced CH4 formation by 43%, similar to other well known methanogenic inhibitors (2-Bromoethanesulfonate, 2-Chlomoethanesulfonate, 2-Mercaptoethanesulfonate). However, ethephon rapidly hydrolyzed to C2H4 and methanogenic activity recuperated completely after C2H4 removal. To slow down the release of C2H4, ethephon was mixed with bio-degradable polymers such as cellulose acetate and applied to paddy soils. We found that compared with the control, the C2H4 release of ethephon slowed down to 90 days, and the CH4 emissions were reduced by 90%. The application of ethephon at lower concentrations did not significantly alter bacterial communities, their relative abundance, and the abundance of methanotrophs, but it significantly reduced archaeal communities and the relative abundance and expression level of methanogens in paddy soils. Results suggest that cellulose acetate-mixed ethephon has great promise to suppress CH4 emissions in rice paddies while ensuring sustainable yields.

This study investigated the offset effect between green manure (GM) application and plastic film mulching (PFM) on soil organic carbon (SOC) stock change during maize cultivation. Within PFM and no-mulching treatments, three different fertilization sub-treatments were applied: (a) chemical fertilizer, (b) barley and (c) hairy vetch. The SOC balance were evaluated by analyzing the net ecosystem carbon budget (NECB). The results showed that the NECB value was negative during maize cultivation regardless of mulching or fertilization condition, indicated SOC loss. The PFM increased maize yield (P

Crop residue or biomass is generally removed from the field as animal feed and fuel in many Asian countries. The impact of this practice on sustaining soil annual net carbon balance (ANCB) has not received much attention for cover crop-rice cropping systems in paddy soil. The influence of cover crop cultivation and biomass incorporation rates on ANCB needs to be evaluated in a rice-based cropping system. Above-ground biomass was harvested and incorporated at 3.0, 6.0 and 12.0 Mg ha−1 (dry weight) 1 week before rice transplanting and carbon (C) inputs and losses were compared with a control treatment i.e. 0 Mg biomass ha−1. The annual net C inputs and outputs significantly increased with the increased biomass incorporation rates. Applied organic C was lost mainly as CO2-C during cover crop cultivation, and as CH4-C and CO2-C during the rice growing season. About 81–90% of total organic C output was lost as CO2-C and 10–19% as CH4-C during the rice growing season. The net ecosystem C balance was negative (− 1402 to − 1523 kg C ha−1) with cover crop cultivation, but it was mostly positive (1071–2652 kg C ha−1) in the rice growing season depending on biomass incorporation rates. About 5.2 Mg ha−1 (43% of total harvest) cover crop biomass needs to be recycled for sustaining soil organic C stocks in paddy field.

In temperate paddy fields, rice is generally cultivated under flooding for 100–140 days during summer season, and thereafter, the soil is left without management under dried soil condition during cold fallow season. In this area rice straw is mostly removed for cattle feeding. Therefore, soil organic carbon (SOC) stock could be decreased with conventional practices, but the seasonal changes of SOC stock have not been evaluated well. To investigate SOC stock changes in temperate rice paddy, two seasonal C balances during rice cropping and fallow season were compared by the net ecosystem C budget (NECB) in the chemical fertilizer (control) and two different green manure treatments for three years. In the control treatment only chemical fertilizer was conventionally fertilized for rice cropping, but maintained without human control during the fallow season. In two green manure treatments, barley and hairy vetch (hereafter, vetch) were cultivated during the fallow season, and their whole biomasses were incorporated before rice transplanting. The conventional soil management with only chemical fertilization decreased small level of SOC stock (minus 0.70–0.84 Mg C ha−1 y−1 of NECB), which was attributed by high harvest removal (approximately 70% of total C input) and mineralized C loss (30%). Cover cropping and its biomass recycling as green manure was effective to increase SOC stock. High C/N ratio of non-leguminous barley produced high biomass yield, and its biomass incorporation significantly increased SOC stock with 1.21–3.43 Mg C ha−1 y−1 of annual NECB. In comparison low C/N ratio of leguminous vetch application increased slightly SOC stock (0.17–1.34 Mg C ha−1 y−1 of NECB), due to low biomass productivity and high mineralized C loss. However, irrespective with fertilization background, approximately 70% of mineralized C loss were occurred during the cold fallow season. Rice grain yields were similar between the control and hairy vetch treatment, but around 10% lower in barley treatment. Conclusively, high C/N ratio of cover crop cultivation during the fallow season could be better to increase SOC stock in mono-rice paddy, but additional nutrient management to increase rice productivity should be developed for barley utilization as green manure.

In temperate mono-rice paddy fields, rice is cultivated for 100–140 days under submerged conditions during the summer period, and thereafter, the field remains under dry conditions during the winter and spring seasons. However, the early developed nitrous oxide (N2O) emission factor (EF) was only based on seasonal (rice cropping period) N2O fluxes, which resulted in lower N2O EF than the default value (0.3%) used by the Intergovernmental Panel on Climate Change (IPCC). Furthermore, the long fallow season may be favorable for nitrification and substantially result in increased N2O emissions. A two-year field experiment was conducted to evaluate the effect of N2O emissions during the dry fallow season on the annual N2O EF. The N2O emission rates were sequentially characterized during the rice cropping and the fallow season under four different levels of nitrogen (N) fertilizer for rice cultivation. The urea was applied at four different (0, 45, 90 and 180 kg N ha−1) levels, and rice was cultivated under submerged conditions during late May to early October. The seasonal N2O fluxes during the rice cropping and fallow seasons clearly increased with increasing N application rates. In the N fertilized plots, the mean N2O emission rates were higher during the fertilized cropping season than the fallow season, but the seasonal fluxes were much higher during the unfertilized fallow season, due to the long dry period. The seasonal N2O EF, which was estimated by the increased N2O flux with N fertilizer, was only 0.0015–0.0017 kg N2O-N kg−1 N during rice cropping. However, the annual N2O EF combining the two seasonal N2O fluxes markedly increased to 0.0028–0.0031 kg N2O-N kg−1 N, which was very close to the N2O EF of the IPCC. Conclusively, the N2O EF in mono-rice paddy fields should be developed using the annual N2O fluxes and not only the cropping seasonal N2O fluxes.

The effective utilization of slag-based Silicon fertilizer (silicate fertilizer) in agriculture to improve crop productivity and to mitigate environmental consequences turns it into a high value added product in sustainable agriculture. Despite the integral role of soil microbiome in agricultural production and virtually all ecosystem processes, our understanding of the microbial role in ecosystem functions and agricultural productivity in response to the silicate fertilizer amendment is, however, elusive. In this study, using 16S rRNA gene and ITS amplicon illumina sequencing and a functional gene microarray, i.e., GeoChip 5, we report for the first time the responses of soil microbes and their functions to the silicate fertilizer amendment in two different geographic races of Oryza sativa var. Japonica (Japonica rice) and var. Indica (Indica rice). The silicate fertilizer significantly increased soil pH, photosynthesis rate, nutrient (i.e., C, Si, Fe, P) availability and crop productivity, but decreased N availability and CH4 and N2O emissions. Moreover, the silicate fertilizer application significantly altered soil bacterial and fungal community composition and increased abundance of functional genes involved in labile C degradation, C and N fixation, phosphorus utilization, CH4 oxidation, and metal detoxification, whereas those involve in CH4 production and denitrification were decreased. The changes in the taxonomic and functional structure of microbial communities by the silicate fertilizer were mostly regulated by soil pH, plant photosynthesis, and nutrient availability. This study provides novel insights into our understanding of microbial functional processes in response to the silicate fertilizer amendment in rice cropping systems and has important implications for sustainable rice production. Keywords: Microbial responses/feedbacks, Silicate fertilization, GeoChip, Functional genes, Illumina sequencing

Excessive application of N fertilizer to rice results in water and atmospheric pollution including greenhouse gas (GHG) emissions. Therefore, N fertilizer management needs to be optimized taking into account grain yield, global warming potential (GWP, Mg CO2 eq. ha−1) and GHG intensity (GHGI, kg CO2 eq. kg−1 grain). However, the tradeoffs between the effects of N rate on rice grain yield, GWP and GHGI have not been adequately evaluated. Therefore, field experiments to determine the effect of N rate (as urea) on yield, GWP and GHGI were conducted in a typical flooded, transplanted rice paddy in a temperate environment. Methane (CH4) and nitrous oxide (N2O) emission rates were determined throughout the entire year (both during growing and fallow seasons) over two years. Rice grain yield showed a quadratic response to N rate, and the maximum yield (6.7–6.8 t ha−1) was achieved at 112–119 kg N ha−1, 50% higher than the yield of the control (0 kg N ha−1). Increasing N rate increased the seasonal N2O flux by 4.56–7.11 g N2O kg−1 N, but N2O flux contributed less than 7% of the total GWP. The GWP was mainly determined by the CH4 flux, which showed a relatively flat quadratic response to N rate, peaking at 124–138 kg N ha−1. Thus, GWP also showed a quadratic response to N rate, peaking at 122–130 kg N ha−1. The GHGI decreased as N rate increased and was the lowest (1.10–1.28 kg CO2-eq. kg−1 grain yield) at 104–112 kg N ha−1, approximately 20% lower than GHGI in the 0 N treatment. In conclusion, the N rate for maximum yield was similar to the N rate for minimum GHGI, mainly because of the small effect of N rate on CH4 emissions and the low magnitude of N2O emissions. Thus, GHGI was largely driven by grain yield, so the N rate for maximum grain yield was similar to the N rate for maximum GHGI. Proper N fertilization is essential in rice farming systems to increase crop productivity and reduce the global warming impact (GWP and GHGI).

Nitrous oxide (N2O) is a major greenhouse gas (GHG) with high global warming potential. A majority of the N2O flux comes from agricultural sources, mainly due to nitrogen (N) fertilization. The soil N2O flux, induced by N fertilization, mainly originated from two different sources, i.e., fertilizer and soil organic nitrogen (SON). It is essential to know the individual contribution of these two different sources in total N2O flux for planning necessary mitigation strategies. It is also indispensable to know the seasonal difference of emission factors (EF) for having more accurate N2O inventory. Therefore, an experiment was conducted in a South Korean upland soil during summer and winter seasons using 15N labeled urea as an artificial N source and source specific N2O emissions were distinguished under different environmental conditions. To characterize the N2O emissions from urea, 0, 50, 100 and 200% of the Korean N recommendation rate was selected for specified crops. The Korean N recommendation rate for red pepper (Capsicum annuum) and garlic (Allium sativum) was 190 and 250 kg N ha−1, respectively. Direct emissions from urea were estimated from the difference of 15N2O flux emitted from 15N-urea treated soil and the natural abundance of 15N2O. From total N2O fluxes, urea originated N2O flux was 0.87% and 0.13% of the applied N in warm and cold seasons, respectively and the rest comes from SON. Nitrous oxide EF in the warm season was 2.69% of applied N and in the cold season that was 0.25%. Nitrous oxide fluxes showed a significant exponential relationship with soil temperature. The results show the necessity of considering the different N2O EF for warm and cold cropping seasons to reduce uncertainty in N2O inventory. The findings of this research may help better understand N2O source partitioning and the emission budget from warm and cold cropping seasons.

Agricultural liming materials are broadly utilized in the world to ameliorate soil acidity. Crushed limestone (CaCO3) and dolomite (MgCO3·CaCO3) are most common liming materials. The CO2 emission coefficient was proposed as 0.12 Mg C per Mg for CaCO3 by the Intergovernmental Panel on Climate Change (IPCC), which indicates that 100% of C in CaCO3 is eventually released to the atmosphere in the form of CO2. However, this assumption appears unlikely based on current knowledge of the very low solubility of CaCO3 and carbonate transport through soil. To develop the direct CO2 emission factor from the C-containing liming materials applied in moderately acidic soil, CaCO3 was applied in a typical temperate upland soil at different levels (0–2 Mg ha−1 yr−1), and the CO2 emission rates were determined using the closed chamber method for two years. The direct CO2 emission factor from CaCO3 was estimated using 13CO2 fluxes from 13C-CaCO3 applied soils. Approximately 0.026 Mg C per Mg of CaCO3 was emitted as CO2 from CaCO3 in cropping lands. This value was much lower than the IPCC default value (0.12 Mg C per Mg of CaCO3). The current CO2 emission coefficient was comparable with the United States Environmental Protection Agency (EPA) emission factor (0.046 Mg C per Mg of CaCO3) from the agricultural field. If the EPA emission factor from the ocean (0.013 Mg C per Mg of CaCO3) is added to the currently developed CO2 emission factor of the inner agricultural field, the total CO2 emission factor from lime may be close to 0.039 Mg C per Mg of CaCO3 in the selected upland soil. Therefore, we propose that the current IPCC guideline value of the CO2 emission factor from lime should be revised as 0.039 Mg C per Mg of CaCO3 for Korean upland soils.

Manure application showed contrasting effects on soil quality and greenhouse gas (GHG) emissions, in particular methane (CH4) emissions in a rice cropping system. Therefore, to mitigate CH4 emissions, stabilized manure like compost is recommended without considering the additional GHG emissions during the industrial processes and soil organic carbon (SOC) stock changes. To determine the integrated effect of compost utilization on the net global warming potential (GWP) of a rice cropping system, the fluxes of GHGs during the whole process were computed using a life cycle assessment (LCA) method. The model framework was composed of GHG fluxes from two compartments: the industrial activities, and the composting and rice cropping processes. Since manure application can increase SOC stock, the annual SOC stock changes were analyzed by the net ecosystem C budget (NECB). Manure applications significantly increased rice productivity and the net primary production (NPP) as a C input source without difference between fresh and composted manures. NPK+fresh manure application significantly increased CH4 and N2O emissions by 81% and 37% over the NPK treatment in rice cropping system, respectively, and depleted SOC stock with 1.3 Mg C ha−1 year−1, due to priming effect. As a result, NPK+fresh manure application increased the net GWP by 80% over the NPK treatment. In comparison, NPK+compost utilization decreased the net GWP by 30% over that of the NPK+fresh manure during the whole process. Manure composting increased the GWP of the industrial processes by 7%, but the 20% reduction of CH4 flux and 0.5 Mg C ha−1 year−1 of SOC stock increase significantly decreased the net GWP during the whole rice cropping process. As a result, the GHG intensity which means the net GWP per gain yield was not different between the NPK+composted manure and the NPK treatments. In conclusion compost application can be a reasonable soil management strategy to reduce GHG emission impact and to increase crop productivity in rice cropping systems.

Biochar utilization is accepted as the most cost-effective practice to mitigate global warming via increase in soil C stock. However, its utilization effect on greenhouse gas (GHG) fluxes was evaluated only within land application without considering industrial processes. To evaluate the net effect of biochar utilization on global warming within whole system boundary, swine manure-saw dust mixture was pyrolyzed under four different temperatures, and GHG fluxes were characterized under with/without syngas recycling systems. To determine GHG fluxes from biochar amended soil, 40 Mg ha‐1 of biochar was mixed with soil and incubated under flooded and dried soil conditions. Finally, the effect of biochar utilization was generalized using net global warming potential (GWP) from industrial process to land application. Under without syngas recycling system, huge amounts of GHGs were emitted during pyrolysis, and GHG fluxes highly increased with increasing pyrolysis temperature, due to direct and indirect GHG emissions from feedstock combustion and electricity, respectively. However, syngas recycling system removed most of GHGs, except for direct N2O and indirect GHG emissions from electricity. Biochar application was very effective to mitigate GHG emissions within soil system boundary, and biochar produced at higher pyrolysis temperature showed higher effectivity in decreasing GHG fluxes. Within the whole system boundary from pyrolysis to soil application, without the installation of syngas recycling system, fresh manure application was more effective than biochar to reduce GHG emissions, regardless of soil water conditions. However, with the installation of syngas recycling system, biochar application was much more effective than fresh manure to decrease GHG fluxes. Biochar produced at higher temperature had higher effectivity to mitigate global warming impacts. In conclusion, to functionally mitigate global warming in soils, biochar should be produced in pyrolysis reactors equipped with syngas recycling system under higher temperature.

Plastic film mulching (FM) became a general practice to enhance crop productivity and its net primary production (NPP), but it can increase greenhouse gas (GHG) emissions. The proper addition of organic amendments might effectively decrease the impact of FM on global warming. To evaluate the feasibility of biomass addition on decreasing this negative influence, cover crop biomass as a green manure was incorporated with different recycling levels (0–100% of aboveground biomass) under FM and no-mulching. The net global warming potential (GWP) which integrated with soil C stock change and GHG (N2O and CH4) fluxes with CO2-equivalent was evaluated during maize cultivation. Under the same biomass incorporation, FM significantly enhanced the grain productivity and NPP of maize by 22–61 and 18–58% over no-mulching, respectively. In contrast, FM also highly increased the respired C loss, which was 11–95% higher than NPP increase, over no-mulching. Irrespective with biomass recycling ratio and mulching system, negative NECB which indicates the decrease of soil C stock was observed, mainly due to big harvest removal. FM decreased more soil C stock by 57–158% over no-mulching, but its C stock was clearly increased with increasing biomass addition. FM significantly increased total N2O and CH4 fluxes by 4–61 and 140–600% over no-mulching, respectively. Soil C stock changes mainly decided net GWP scale, but N2O and CH4 fluxes negligibly influenced. As a result, FM highly increased net GWP over no-mulching, while this net GWP was clearly decreased with increasing biomass application. However, cover cropping, and its biomass recycling was not enough to compensate the negative impact of FM on global warming. Therefore, more biomass incorporation might be essential to compensate this negative effect of FM.

Soil C sequestration is widely regarded as the most reasonable way to mitigate global warming. Traditionally, a high amount of organic carbon (OC) input is strongly recommended to increase soil organic carbon (SOC) stocks in croplands. However, according to the whole-soil saturation theory, stable SOC (mineral-associated SOC) accumulation can be limited at a certain point, relying on silt and clay contents. Most studies based on the theory were conducted in aerobic soil condition. This relationship is still uncertain in a rice paddy that makes up 10.8% of total arable land and has an anaerobic soil environment. In this study, we investigated high OC addition can enhance soil C sequestration in a rice paddy. We added different OC levels (0.5, 2.0, 2.9, and 4.6 Mg C ha-1 yr-1) in rice paddy by incorporating cover crop biomass for nine years. SOC stock and soil saturation degree were determined. Unprotected, sand-associated, silt-associated, and clay-associated SOC were separated via density and size fractionation. Respired C losses (CO2-C and CH4-C) were monitored using the static closed chamber method. SOC stock did not linearly increase with higher amount of OC input. The carbon sequestration efficiency (i.e. the increase of SOC per unit of OC input) decreases with the amount OC added. Higher OM input significantly increased unprotected labile SOC content. Unprotected SOC (-3) exponentially increased as the SOC saturation degree was higher. On the other hand, stable SOC content did not exhibit a linear relationship with the SOC saturation degree. The higher OC addition level exponentially increased respired C loss. In particular, C loss via CH4 was more sensitive to high OC addition. We conclude that higher OC addition in rice paddy without consideration in terms of SOC stock saturation point can accelerate global warming by increasing labile SOC accumulation and CH4 emission.

Excessive nutrient balance is a very crucial issue for environmental hazards. The constant addition of high-amounts of nutrient sources in agricultural production generates negative environmental conditions in Korea and Japan yet to be resolved. Therefore, it is obligatory to comprehend the nutrient (nitrogen (N) and phosphorus (P)) balance that is assessed by the difference between nutrient input and output in the soil surface in Korea and Japan. Among 34 Economic Co-operation and Development (OECD) countries, Korea and Japan had the highest N and P balances and thus both countries are primarily responsible for severe environmental pollution via nutrient release. The cultivable land area in both countries has constantly decreased during 1990–2017 at approximately 20 and 15% in Korea and Japan, respectively. Even N and P use efficiency sharply decreased with increasing N and P balance in both targeted countries. Japanese P balance, Korean N and P balances were decreased after the mid-1990s whereas, Japanese N balance almost unchanged for the last 28 years. Unlike chemical fertilizer input, Korean manure input level significantly increased from 78 kg N ha−1 in 1990 to 157 kg N ha−1 in 2017. Japanese manure input level was higher than that of chemical fertilizer without any big change for the last 28 years. The lion share of high N and P balance in both countries could generate from manure inputs, therefore, the number of livestock and their produced debris need to be used with more cautious for the reduction of national N and P surpluses at a benchmark level. These findings ensure to make a more environment friendly policy that can further reduce nutrient balance as well as improve soil health.

Winter cover crop cultivation and its biomass recycling as green manure (GM) were accepted as an ideal nutrient management practice in temperate organic farming fields. Since its biomass growth was boosted with air temperature rising from late Spring to early Summer, this stage overlapped with cash crops' seeding or transplanting. Thus, organic farmers were suffering from low crop productivity, due to delayed mineralization of incorporated biomass. To accelerate the mineralization of biomass nutrients and control weeds, plastic film mulching (PM) was broadly utilized in organic farming fields of temperate-monsoon climate region. However, the effect of PM on increasing nutrient use efficiency was not properly quantified in GM amended soil. To determine the effect of PM on crop productivity and nutrient use efficiency in GM amended soils, PM and no-mulching treatments were installed under different levels of GM biomass amended soils (0, 25, 50 and 100% of harvested aboveground biomass). The biomass productivity of barley and hairy vetch mixture as cover crop and biomass nitrogen productivity were dramatically increased from the mid May to the early June. PM significantly improved soil temperature and moisture regimes during maize cropping seasons, and then increased inorganic N (NH4+ and NO3-) contents in soils. These improved soil properties under PM highly increased maize productivity and nitrogen use efficiency (NUE). Comparing with no-mulching, as GM application level was increased, the effect of PM on increasing maize productivity became greater, but its effect on increasing NUE became smaller. In conclusion, PM could be very useful tool to improve productivity and NUE of cash crop maize in organic cropping fields, in which the harvesting time of GM biomass might be sustained to increase GM biomass productivity.

In rice paddy, the closed chamber method is broadly used to estimate methane (CH4) emission rate. Since rice plants can significantly affect CH4 production, oxidation and emission, rice plantation inside the chamber is standardized in IPCC guidelines. Methane emission rate is calculated using the increased concentration inside the headspace. Biomass growth might decrease the headspace volume, and thus CH4 emission rates might be overestimated. To evaluate the influence of chamber headspace decreased by rice plant development on CH4 emission rates, five Korean rice cultivars were cultivated in a typical rice paddy, and physical volume changes in rice biomass were assayed using water displacement method. The recommended acrylic closed chambers (H. 1.2 m x W. 0.6 m x L. 0.6 m) were installed, and eight rice plants were transplanted inside the chamber with the same space interval with the outside. Biomass growth significantly decreased the headspace volume of the chamber. However, this volume covered only 0.48–0.55% of the closed chamber volume at the maximum growth stage. During the whole cropping period, mean 0.24–0.28% of chamber headspace was allocated by plant biomass, and thus this level of total CH4 emissions was overestimated. However, this overestimation was much smaller than the errors coming from other investigation processes (i.e., chamber closing hour, temperature recording, inconstant flooding level, different soil environments, etc.) and rice physiological changes. In conclusion, the influence of physical biomass volume inside the closed chamber was negligible to make the error in total CH4 emission assessment in rice paddies.