Context As wild boar populations continue to grow and their range expands globally, human-wildlife conflicts, such as crop damage, have become widespread. Effective management of crop-foraging wild boars requires a detailed understanding of their foraging habitsAims This study investigates wild boar feeding habits during the rice ripening and harvesting season in a Japanese rice-growing region, aiming to identify habitat landscape drivers of rice and natural plant consumption.Methods We assessed wild boar feeding habits by using the mixing models based on C-N stable isotope values from the livers of 57 wild boars and their food resources. Generalised linear mixed models were used to understand the association between wild boar sex and habitat landscape structure as well as the contributions of rice and natural plants.Key results Natural plants were the primary food resource for most individuals (48/57), whereas rice was the main component for only a few (5/57). For wild boars, the landscape analysis indicated that paddy coverage in their habitat was positively and negatively associated with rice and natural plant contributions respectively. Additionally, rice contribution increased in male boars.Conclusions Individual wild boars exhibited heterogeneous contributions to rice damage. Furthermore, wild boars in areas with extensive rice cultivation relied more on rice and consumed fewer natural plants, suggesting that easier access to paddy fields leads to a dietary shift.Implications Overall, we recommend a more strategic focus on managing wild boars in areas with extensive paddy fields rather than targeting the entire population to more effectively control crop-foraging behaviour.

Abstract Rhizosphere oxidation is a key adaptive mechanism in reductive soil environments, in which oxygen released from roots alters rhizosphere redox conditions and regulates biogeochemical processes. Rice plants possess an internal oxygen transport system, and radial oxygen loss (ROL) from roots is closely associated with root development. However, the spatial patterns of ROL in soil and their relationships with root traits remain poorly characterized. In this study, we developed a multimodal imaging system that integrates planar oxygen optodes with X-ray computed tomography to simultaneously visualize rhizosphere oxidation and root development in rice. Daily time-course tracking of individual crown roots revealed dynamic changes in the spatial distribution and magnitude of rhizosphere oxygen in relation to root elongation and aging. Root thickness was positively correlated with dissolved oxygen levels near root tips. Genotypic comparisons further identified a cultivar with reduced rhizosphere oxidation despite possessing thicker roots among the tested genotypes, thereby indicating the involvement of additional physiological processes. Overall, these findings demonstrate that rhizosphere oxidation is regulated by root growth stage and thickness and dynamically modulated during root development.

Rice paddies are substantial sources of methane emissions, with CH4 released into the atmosphere through three pathways: molecular diffusion of dissolved methane across the atmosphere-water boundary, ebullition of gas bubbles, and diffusive transport through the aerenchyma tissue of rice plants. This study aimed to analyze seasonal variations in CH4 fluxes separately via ebullition and rice plants and to explore the potential relation between in situ gas volume and CH4 emissions. Field monitoring of CH4 emissions, gas-filled porosity (that is, bubble volume), and soil temperature was conducted in a rice paddy with four different treatments: plots with/without rice plants (Oryza sativa ‘Koshihikari’) and with/without straw application. Results indicated that both total CH4 flux and CH4 ebullition were higher during the ripening stage for plots without straw application, and over 60

Context While the individual benefits of technologies like alternate wetting and drying (AWD), site-specific nutrient management (SSNM), mechanical transplanting, laser-guided land leveling (LLL), and herbicide application are well-documented, limited information exists on their combined effects on rice productivity and profitability. Objectives This study hypothesized that integrating resource-use efficient technologies could offer compounded benefits in yields and reduced production costs. The study aimed to assess the cost-effectiveness and grain yields of bundled technologies for rice, evaluating whether bundling could enhance yields, reduce production costs, and improve gross margin under farmers' field conditions. Methods On-farm participatory field trials were conducted over two dry seasons in the Philippines. Technology combinations were grouped as treatments (T) to reflect increasing bundling levels: T1 (farmers' practice (FP) with continuous flooding or CF), T2 (CF with mechanical transplanting, SSNM, and pre-emergence herbicide or PH), T3 (T2 with LLL), T4 (FP with AWD), T5 (AWD, mechanical transplanting, SSNM, and PH), and T6 (T5 with LLL). Results Bundles involving LLL (T3) significantly increased the unit cost of production (P < 0.05) but did not result in proportional yield or gross margin increases. The outcome was attributed to exposure to less fertile soil after cut-and-fill operations and the high rental fee of LLL. However, the AWD in T6 with LLL mitigated these effects, resulting in no significant impact on yield. T5 balanced production costs and yield, offering a more economically viable approach than T3. The variability in yields and gross margins across treatments suggests that the expected benefits of higher yields and reduced costs from bundling technologies were inconsistent, with some treatments showing no advantages over farmers’ practices. Conclusion The bundles combining AWD, SSNM, mechanical transplanting, and pre-emergence herbicide offered a balanced approach to cost-efficiency and productivity. Bundles involving LLL have increased production costs without corresponding yield or gross margin gains. Implications of the study The results underscore the complexity of bundled agricultural technologies, particularly in the context of smallholder systems. Benefits vary significantly depending on the technology combination, environmental conditions, and management practices, emphasizing the need for site-specific approaches when introducing new technologies. The findings provide valuable insights for bundling rice farming technologies with similar agroecosystems like the study site to enhance resource use management.

Methane (CH4) produced in rice paddy soil is transported to the atmosphere mainly via the rice plants and partly bubbling events (ebullition). Recent studies have shown that ebullition is more significant than previously thought fields planted with the popular Japanese cultivar 'Koshihikari'. It remains unclear whether the substantial contribution of ebullition is unique to this specific cultivar, as no previous reports have compared plant-derived and bubbling fluxes separately among various cultivars. Therefore, we planted 22 genetically diverse rice cultivars and measured plant-mediated and bubbling fluxes at three growth stages. Both fluxes, as well as the contribution of bubbling to the total flux, differed among the cultivars. The plant-mediated flux in Koshihikari was similar to or less than those other cultivars, whereas the bubbling flux and its contribution to total flux were larger, especially at the later stage. The absence of a correlation between plant-mediated flux and dissolved CH4 in the soil water at the later stage suggests that varietal differences in CH4 entry from the soil to the plant or gas flow permeability in the plant, rather than the pool size of CH4 in the soil, control the plant-mediated flux. On the other hand, the increase in bubbling flux associated with plant maturation and its close correspondence with dissolved CH4 concentration indicate that bubbling flux was controlled the size of CH4 pool in the soil, which likely increased with senescence and decay of rice roots. A low correspondence between panicle weight and CH4 emissions points to the potential for breeding high-yielding rice cultivars with low CH4 emissions

While potential changes in the growth and grain yield of rice plants under climate change have been extensively studied, much less is known about how climate change affects the decomposition processes of rice residue in the soil. Increasing atmospheric CO2 concentration can alter the chemical composition of crops, which in turn can affect the decomposability of crop residues and carbon turnover in soils. We conducted free-air carbon dioxide (CO2) enrichment (FACE) experiments over 2 years, using nine rice cultivars, to test whether elevated CO2 concentration by 200 ppm (e[CO2]) and cultivar selection could affect rice straw decomposability in soil. Results showed that the concentrations of nitrogen (N, reduced by 4.3%), magnesium (Mg, reduced by 7.6%), and manganese (Mn, reduced by 27.4%) in straw were significantly lowered under e[CO2]. e[CO2] significantly enhanced the initial straw decomposition rates by an average of 30%, measured as cumulative CO2 production during a 36-h incubation period. The decomposition rates also varied substantially among the rice cultivars, with a 1.6-fold difference observed. The stimulatory effect of e[CO2] on straw decomposition was mainly attributed to a 30% decrease in lignin and a 20% increase in nonstructural carbohydrate concentrations, whereas the differences in straw decomposability among cultivars were significantly correlated with Mn concentration. This study provided evidence that both e[CO2] and the selection of rice cultivars could affect the C turnover rates via changes in the chemical composition of incorporated straw in soils.

A 3-year field trial was conducted to evaluate the impact of Azolla as green manure (AGM) applied in a lowland paddy field at the rate of 7.0 g N m(-2) in combination with floating Azolla cover (herein Cover) on rice yield in comparison with inorganic fertilizer (NPK) alone or NPK + Cover (herein NPK-amended) treatments. In the initial year, AGM + Cover significantly lowered the rice grain yield by an average of 36.5% compared with NPK-amended treatments. This decline was associated with fewer panicles, total spikelets, and a lower ratio of filled grains, and was attributed to the gap in time between nutrient release from Azolla and nutrient demand from rice during the growth period as reflected in a smaller nitrogen content in the rice grains. Conversely, successive application of AGM + Cover in the 2(nd) and 3(rd) years of rice growth significantly increased grain yields to levels equal to those of NPK-amended treatments. This recovery was ascribed to an increase in total spikelet number, an improved filled grain ratio, and an increase in 1000-seed weight. The significant (p < 0.05) upward trend in rice grain yield following AGM + Cover amendment across the 3 years (392.9-745.9 g m(-2)) was likely due to enhanced soil nutrient availability associated with residual effects of AGM amended in the previous crops. These results indicate that sustainable rice yield can be achieved by replacing chemical fertilizers with Azolla as manure in the long term. However, a combined application of organic and judicial inorganic fertilizer management as a booster is recommended in the initial year.

Methane (CH4), the second-most-potent greenhouse gas, is produced by methanogens under anaerobic conditions. Tropical peat swamp forests, which are widely distributed in Southeast Asia, have recently been subjected to large-scale deforestation and conversion to agricultural land. The pH of low-pH (acidic) tropical peat soils on agricultural lands is generally controlled to promote plant growth. Unintended waterlogged conditions in agricultural lands during the wet season can create an anaerobic environment in which methanogens are active. In this study, surface peat soil collected from a tropical peat swamp forest in Central Kalimantan, Indonesia, was examined to clarify the effect of increasing pH on CH4 production. Soil samples were prepared at varying pH (3.4, 4.7, 6.6, and 7.7) by adding calcium hydroxide and incubated under anoxic conditions. Soil remained under dark and cool conditions for years before incubation. CH4 production increased with incubation time at all pH levels. Overall, soils at higher pH showed significantly greater CH4 production compared with peat at pH 3.4 (control) at most measurement points during a 76-day incubation. Analysis of the phylogenetic composition of archaeal and bacterial communities in peat after a 76-day incubation showed that the relative abundance of Euryarchaeota (Methanobacteria + Methanomicrobia), organisms that produce CH4, increased from pH 3.4 (similar to 0%) to pH 4.7 (5.3 %), pH 6.6 (8.7 %), and pH 7.7 (8.7 %). This suggests that increasing the pH of tropical peat enhances CH4 production by increasing the proportion of methanogens. It should also be noted that the anaerobic microbe populations in tropical peat can survive and recover after long-term cold storage.

Diurnal fluctuations in methane (CH4 ) emission are frequently observed in rice paddy fields, yet the driving mechanisms behind these variations are not fully understood. We posited that the observed diurnal patterns are predominantly due to temperature-dependent bubbling emissions (ebullition). To investigate this hypothesis, we conducted measurements of CH4 emission in a Japanese rice paddy using static chambers coupled with a high-time-resolution CH4 analyzer that allowed us to partition the total flux into its two principal components: plant-mediated transport and ebullition. Diurnal variation in the total flux was minimal during the early parts of reproductive growth (panicle formation and booting stages), when plant-mediated emission was dominant. At a later stage (heading period), ebullition accounted for 43%-70% of the total emission, and CH4 emission via both pathways varied diurnally; however, the diurnal range was much greater for bubbling emission (ratio of maximum to minimum = 3.5) than for plant-mediated emission (ratio of maximum to minimum = 1.4). The magnitude of emissions due to ebullition depended on the temperature, but was greater during the flux-increasing phase in the morning than the flux-decreasing phase in the afternoon even at the same temperature, forming a hysteresis in the flux versus temperature relationship. These findings support our hypothesis and indicate that abiotic processes, such as a change in the solubility of gases and the temperature dependence of the gas-phase volume (Charles's law), may play a central role in shaping the diurnal pattern of the CH4 ebullition.

Global warming can accelerate soil organic matter (SOM) decomposition resulting in faster carbon loss and positive climate-C feedback. Previous studies on response of SOM decomposition to climate change mainly focus on plow soil layer. However, the effects of elevated CO2 and soil warming on soil organic carbon (SOC) and total nitrogen (TN) contents and mineralization are rarely studied in subsoil layer. In this study, soil samples were collected from the 0–50-cm paddy soil layer of the Tsukuba free-air CO2 enrichment experimental site with elevated CO2 (+200 ppm) and soil warming (+2 °C), Japan, after 5-year rice growth season. The amounts of SOC, TN, δ13C, and δ15N were analyzed. A 4-week anaerobic incubation experiment was conducted to measure C decomposition and N mineralization potentials. Due to the intrinsic variation in SOC and TN contents in soil layers and fields, the effects of elevated CO2 and soil warming on C decomposition and N mineralization potentials could not be determined here. However, the effect of elevated CO2 on δ13C was only found in 0‒10-cm soil layer. In the 0–50-cm soil profiles, significant correlations were observed among SOC and TN, δ13C and δ15N, decomposed C and mineralized N, and δ13C in decomposed C. The variables associated with soil C and N pools, and dynamics showed large spatial heterogeneity within paddy field, due to variation in the original land use history. Therefore, great caution should be exercised when evaluating the effects of elevated CO2 and temperature on SOM decomposition and sequestration in paddy soil profiles.

Methane (CH4) produced in rice paddy soil is transported to the atmosphere mostly via the rice plants or by bubbling events (ebullition) with the former believed to be the dominant pathway. However, recent studies have shown that ebullitions occurred more significantly than previously thought in a rice field planted with the popular Japanese inbred variety ‘Koshihikari’. It remains unclear if the substantial contribution of ebullition is unique to this specific variety, as no previous reports have compared plant-derived and bubbling flux separately among various varieties. Therefore, we planted 22 genetically diverse rice varieties and measured plant-mediated and bubbling fluxes at three different growth stages. The results showed that plant-mediated and bubbling fluxes, as well as the bubbling contribution to total flux, differed among the varieties. Koshihikari ehxibited plant-mediated flux similar to or less than the other varieties at all measurement stages, whereas the bubbling flux and its contribution to total flux were larger, especially at the later stage. Plant-mediated flux showed no correlation to the dissolved CH4 concentration in soil water at the later stage, suggesting that factors controlling CH4 transport, rather than the pool size of CH4 in the soil, control this pathway. On the other hand, the increase in bubbling flux associated with plant maturity and its close correspondence with dissolved CH4 concentration indicated that bubbling flux was controlled by the size of CH4 pool in the soil, which likely increased with senescence and decay of rice roots. A low correspondence between panicle weight and CH4 emissions points to the potential for breeding ideal rice varieties that are high- yielding with low CH4 emissions.

Climate change and water scarcity threaten the sustainability of rice production systems. Alternate wetting and drying (AWD) is a promising option to reduce methane (CH4) emission from irrigated paddy fields. However, its effect on rice yield remains to be clarified. Organic amendment can increase rice yield but may also increase CH4 emission. We therefore hypothesized that the combination of AWD with organic amendment could both increase rice yield and decrease CH4 emission. We carried out field experiments in six consecutive rice seasons during 2019 - 2022 in Central Java, Indonesia. We examined the effect of water management (continuous flooding [CF] and AWD) with (+M) and without (-M) the amendment of cattle manure as a locally available organic matter on rice growth and yield and the emissions of CH4 and nitrous oxide (N2O). AWD significantly (p < 0.05) decreased CH4 emission by 29% but marginally (p < 0.1) increased N2O emission by 10% relative to CF. There was no significant effect of AWD alone on rice yield. AWD significantly increased water productivity (the ratio of rice yield to irrigated water volume) by 50%. Cattle manure amendment significantly increased CH4 emission by 12% and rice yield by 5% but did not affect N2O emission. The combination effect of AWD+M relative to CF-M (control) was additive and resulted in a 7% increase in rice yield, a 19% decrease in the global warming potential (GWP) of CH4 + N2O emissions during both growing and fallow periods, and a 24% decrease in yield-scaled GWP. Our results indicated that the combination of AWD with cattle manure amendment would be a promising means to increase rice yield while reducing total soil greenhouse gas emission from irrigated rice paddies.

The demand for biomass energy production in the Philippines has led to substantial rice husk ash (RHA) generation. We combined alternate wetting and drying (AWD) and varying RHA rates (10, 20, and 30 t ha–1) to evaluate the yield, water productivity (WP), and greenhouse gas (GHG) emissions in paddy rice for four cropping seasons (CS). We compared these treatments with continuous flooding (CF) and no RHA as controls. The RHA decreased N2O emissions by 8–22

Improving crop yield potential through an enhanced response to rising atmospheric CO2 levels is an effective strategy for sustainable crop production in the face of climate change. Large-sized panicles (containing many spikelets per panicle) have been a recent ideal plant architecture (IPA) for high-yield rice breeding. However, few breeding programs have proposed an IPA under the projected climate change. Here, we demonstrate through the cloning of the rice (Oryza sativa) quantitative trait locus for MORE PANICLES 3 (MP3) that the improvement in panicle number increases grain yield at elevated atmospheric CO2 levels. MP3 is a natural allele of OsTB1/FC1, previously reported as a negative regulator of tiller bud outgrowth. The temperate japonica allele advanced the developmental process in axillary buds, moderately promoted tillering, and increased the panicle number without negative effects on the panicle size or culm thickness in a high-yielding indica cultivar with large-sized panicles. The MP3 allele, containing three exonic polymorphisms, was observed in most accessions in the temperate japonica subgroups but was rarely observed in the indica subgroup. No selective sweep at MP3 in either the temperate japonica or indica subgroups suggested that MP3 has not been involved and utilized in artificial selection during domestication or breeding. A free-air CO2 enrichment experiment revealed a clear increase of grain yield associated with the temperate japonica allele at elevated atmospheric CO2 levels. Our findings show that the moderately increased panicle number combined with large-sized panicles using MP3 could be a novel IPA and contribute to an increase in rice production under climate change with rising atmospheric CO2 levels.

Azolla, a common aquatic fern has been used successfully as a dual crop with lowland rice. It grows rapidly and fixes atmospheric nitrogen for rice paddy. However, its ecological significance especially on greenhouse gases emissions remains unclear. Three independent experiments -two pot (2016 and 2017), and one field in 2019- were conducted to investigate the effects Azolla (A. filiculoides Lam.) either or both as dual cropping and green manure along with rice plant on simultaneous methane (CH4) and nitrous oxide (N2O) emissions from constantly flooded paddy soil. Under pot setups, dual cropping Azolla as a cover with rice plant significantly decreased seasonal CH4 emission by 34.7%, with no effect on N2O emissions. Suppressed CH4 emission was likely due to an increase in dissolved oxygen concentration and redox potential at the soil-water interface simulating CH4 oxidation. However, incorporation of Azolla as green manure into the soil plus dual crop in conjunction with chemical fertilizers significantly increased CH4 emission by 37.5% but decreased N2O emission by 74.5%. The significantly higher CH4 and lower N2O emissions were attributed to the readily decomposable incorporated Azolla, acting both as a source of CH4 production and N2O reduction. Contrary to the pot observations, application of Azolla as a dual crop in conjunction with chemical fertilizer or incorporated as green manure plus dual cropping in the field did not significantly affect seasonal CH4 emissions, but significantly increased cumulative N2O emissions at the middle rice growth stages by 645%—816%, and the total seasonal emission 3.4-fold. The higher N2O emissions were partly attributed to large quantities of exogenous organic carbon resulting from the accelerated growth and subsequent senescence of Azolla cover applied as a dual crop as impacted by higher summer air temperatures. Our observations suggest that dual cropping of Azolla with rice has the potential to reduce CH4 emissions from flooded rice paddies. Conversely, incorporation of Azolla as green manure into the paddy soil plus dual cropping in conjunction with or without chemical fertilizers indicates an inconsistent relationship between CH4 and N2O emissions. Long-term studies are needed to evaluate the relationship between leguminous cover crops and their effects on factors influencing CH4 and N2O emissions from continuously flooded rice paddies.

Rice is the main staple food for more than half of the world’s population, but rice cultivation is a significant source of atmospheric methane (CH4). Alternate wetting and drying (AWD) reduces CH4 emission from paddy field, but the effect on rice yield remains unclear. Organic soil amendment increases grain yield but simultaneously increases CH4 emission. Therefore, the combination of AWD and organic amendment may compensate for each other’s shortcomings. The objective of this study was to assess whether AWD and organic amendment can increase rice yield while mitigating CH4 emission. The experiments were conducted in a farmer’s paddy field in Thua Thien Hue province, Vietnam, during five consecutive rice growing seasons in 2019–2021. Two water management practices, continuous flooding (CF) and AWD, with (+O) or without (−O) the application of a commercially available organic fertilizer were examined under normal cultivation conditions. Compared with CF, AWD significantly reduced CH4 emission by 34 %, increased nitrous oxide (N2O) by 46 %, and increased grain yield by 4.4 %. The +O treatment significantly increased the yield by 3.7 % relative to −O. Relative to CF−O by season, AWD+O significantly increased the yield. The integrated global warming potential of CH4 and N2O emissions was decreased by 33 % and irrigation water use was reduced by 33 % in AWD plots relative to that in CF plots. These results indicate that AWD by itself has the potential to increase rice yield as well as reduce CH4 emission, and the combination of AWD with organic amendment would ensure yield increase.

Abstract The diurnal variation in methane (CH4) emission commonly observed in rice paddies has been linked to changes in air and soil temperatures. The temperature dependence is not simple, however, and the mechanisms underlying it in relation to the diurnal variation are still poorly understood. Here, we investigated the diurnal variation of CH4 flux and its relationship with air temperature in a Japanese paddy by dividing the total flux into two major pathways, plant-mediated and bubbling emission. The diurnal variation of total flux was minimal at the early parts of reproductive growth (panicle formation and booting stages), when plant-mediated emission was dominant. At a later stage (heading period), ebullition accounted for 43–70% of the total emission, and CH4 emission via both pathways varied diurnally; however, the diurnal range was much greater for bubbling emission (ratio of max. to min. = 3.5) than for plant-mediated emission (ratio of max. to min. = 1.4). The Bubbling emission depended on the temperature, but the emission was greater during the flux-increasing phase in the morning than the flux-decreasing phase in the afternoon even at the same temperature, forming a hysteresis in the flux versus temperature relationship. These results indicate that abiotic processes, such as a change in the solubility of gases and the temperature dependence of the gas-phase volume (Charles’s law), may play a central role in shaping the diurnal pattern of the CH4 ebullition.

Paddy fields are a major source of atmospheric methane, a greenhouse gas produced by methanogens and consumed by methanotrophs in flooded soil. The inoculation of rice seeds with the bacterium Azoarcus sp. KH32C alters the rice root-associated soil bacterial community composition. The present study investigated the effects of KH32C-inoculated rice cultivation on soil methanogens and methanotrophs involved in methane emissions from a rice paddy field. KH32C-inoculated and non-inoculated rice (cv. Nipponbare) were cultivated in a Japanese rice paddy with and without nitrogen fertilizer. Measurements of methane emissions and soil solution chemical properties revealed increases in methane flux over the waterlogged period with elevations in the concentrations of dissolved methane, dissolved organic carbon, and ferrous iron, which is an indicator of soil reduction levels. Reverse transcription quantitative PCR and amplicon sequencing were used to assess the transcription of the methyl-coenzyme M reductase gene (mcrA) from methanogens and the particulate methane monooxygenase gene (pmoA) from methanotrophs in paddy soil. The results obtained showed not only the transcript copy numbers, but also the compositions of mcrA and pmoA transcripts were related to methane flux. KH32C-inoculated rice cultivation recruited soil methanogens and methanotrophs that suppressed high methane synthesis, increased methane consumption, and decreased methane emissions by 23.5 and 17.2% under non-fertilized and nitrogen-fertilized conditions, respectively, while maintaining rice grain yield. The present study demonstrated the mitigation of paddy field methane emissions arising from the use of KH32C in rice cultivation due to its influence on the compositions of soil methanogen and methanotroph populations.