Continuous Flooding Treatment Research Articles

Reducing greenhouse gas emissions from rice cultivation applied with melaleuca and rice husk biochar in the Vietnamese Mekong Delta

ABSTRACT Biochar application is considered a potential approach to mitigating greenhouse gas emissions (GHGs) from the agricultural sector and improving soil physicochemical properties. Thus, we conducted a field experiment to examine the efficacy of biochar application rates in combination with water management practices on soil methane (CH4) and nitrous oxide (N2O) emissions and carbon increment in the Vietnamese Mekong Delta (VMD). Rice husk biochar (RB) and Melaleuca biochar (MB) were incorporated in the topsoil (0–20 cm) at 5 and 10 Mg ha−1, followed by the water management regimes of continuous flooding (CF) and an alternative wetting and drying (AWD). The results identified that biochar application rates and water management measures were major factors in decreasing CH4 and N2O emissions. Compared with the conventional practice, the RB and MB amendment in the rice fields under CF practices reduced 12.9–21.3% of total GHGs (tGHGs), while biochar incorporation under the AWD management practice reduced from 22.3% to 30.5% tGHGs. Compared to CF treatments, biochar amendment concerning the AWD regime lowered from 25.4% to 31.6% tGHGs. Increasing biochar from 5 to 10 Mg ha−1 did not reduce tGHGs considerably. We identified that biochar application significantly increased grain yields from 12.8% to 20.6% under the CF management practice, while the percentage varied from 2.5% to 3.8% for the AWD practice. Similarly, higher grain yields were achieved from 4.9% to 13.7% by applying AWD compared to the CF treatments. Our findings showed that although higher biochar application rates could reduce the tGHGs, the difference in biochar types and water management applications in connection with the tGHGs was neglectable. Incorporating biochar enhanced soil bulk density and porosity under AWD and CF practices. Going forward in further studies, we recommend a long-term biochar application in the VMD’s low-lying paddy fields with a broader range of biochar rates under different soil types.

Low pe+pH inhibits Cd transfer from paddy soil to rice tissues driven by S addition

Both soil irrigation and sulfur (S) are associated with the precipitation of cadmium (Cd)-sulfide in paddy soil, their interaction affecting on Cd solubility and extractability is still unknown. This study primarily discusses the effect of exogenous S addition on the bioavailability of Cd in paddy soil under unsteady pe + pH conditions. The experiment was treated with three different water strategies: continuous dryness (CD), continuous flooding (CF), and alternating dry-wet cycles for one cycle (DW). These strategies were combined with three different S concentrations. The results indicate that the CF treatment, particularly when combined with S addition, had the most significant effect on reducing pe + pH and Cd bioavailability in the soil. The reduction of pe + pH from 10.2 to 5.5 resulted in a decrease in soil Cd availability by 58.3%, and Cd accumulation in rice grain by 52.8%, compared to the other treatments. While it was more conducive to the formation of iron plaque on the root surface in DW treatment with S addition at rice maturing stage and enhanced the gathering of Fe/S/Cd. Structural equation model (SEM) analysis further confirmed a significant negative correlation (r = −0.916) between the abundance of soil Fer-reducing bacteria (FeRB) and sulfate-reducing bacteria (SRB) like Desulfuromonas, Pseudomonas, Geobacter, and the Cd content in rice grains. This study provides a basic mechanistic understanding of how soil redox status (pe + pH), S addition, and FeRB/SRB interacted with Cd transfer in paddy soil-rice tissues.

Sulfur fertilization and water management ensure phytoremediation coupled with argo-production by mediating rhizosphere microbiota in the Oryza sativa L.-Sedum alfredii Hance rotation system

Sulfur (S) fertilizers, water management and crop rotation are important agronomic practices, related to soil heavy metal bioavailability. However, the mechanisms of microbial interactions remain unclear. Herein, we investigated how S fertilizers (S0 and Na2SO4) and water management affected plant growth, soil cadmium (Cd) bioavailability, and rhizospheric bacterial communities in the Oryza sativa L. (rice)-Sedum alfredii Hance (S. alfredii) rotation system through 16S rRNA gene sequencing and ICP-MS analysis. During rice cultivation, continuous flooding (CF) was better than alternating wetting and drying (AWD). CF treatment decreased soil Cd bioavailability by the promotion of insoluble metal sulfide production and soil pH, thus lowering Cd accumulation in grains. S application recruited more S-reducing bacteria in the rhizosphere of rice, whilst Pseudomonas promoted metal sulfide production and rice growth. During S. alfredii cultivation, S fertilizer recruited S-oxidizing and metal-activating bacteria in the rhizosphere. Thiobacillus may oxidize metal sulfides and enhance Cd and S absorption into S. alfredii. Notably, S oxidation decreased soil pH and elevated Cd content, thereby promoting S. alfredii growth and Cd absorption. These findings showed rhizosphere bacteria were involved in Cd uptake and accumulation in the rice-S. alfredii rotation system, thus providing useful information for phytoremediation coupled with argo-production.

Water Management Impacts on Chromium Behavior and Uptake by Rice in Paddy Soil with High Geological Background Values.

Chromium (Cr) is an expression toxic metal and is seriously released into the soil environment due to its extensive use and mining. Basalt is an important Cr reservoir in the terrestrial environment. Cr in paddy soil can be enriched by chemical weathering. Therefore, basalt-derived paddy soils contain extremely high concentrations of Cr and can enter the human body through the food chain. However, the water management conditions' effect on the transformation of Cr in basalt-derived paddy soil with high geological background values was less recognized. In this study, a pot experiment was conducted to investigate the effects of different water management treatments on the migration and transformation of Cr in a soil-rice system at different rice growth stages. Two water management treatments of continuous flooding (CF) and alternative wet and dry (AWD) and four different rice growth stages were set up. The results showed that AWD treatment significantly reduced the biomass of rice and promoted the absorption of Cr in rice plants. During the four growth periods, the root, stem and leaf of rice increased from 11.24-16.11 mg kg-1, 0.66-1.56 mg kg-1 and 0.48-2.29 mg kg-1 to 12.43-22.60 mg kg-1, 0.98-3.31 mg kg-1 and 0.58-2.86 mg kg-1, respectively. The Cr concentration in roots, stems and leaves of AWD treatment was 40%, 89% and 25% higher than CF treatment in the filling stage, respectively. The AWD treatment also facilitated the potential bioactive fractions conversion to the bioavailable fraction, compared with the CF treatment. In addition, the enrichment of iron-reducing bacteria and sulfate-reducing bacteria with AWD treatment also provided electron iron for the mobilization of Cr, thus affecting the migration and transformation of Cr in the soil. We speculated that the reason for this phenomenon may be the bioavailability of Cr was affected by the biogeochemical cycle of iron under the influence of alternating redox. This indicates that AWD treatment may bring certain environmental risks in contaminated paddy soil with high geological background, and it is necessary to be aware of this risk when using water-saving irrigation to plant rice.

Eddy covariance assessment of alternate wetting and drying floodwater management on rice methane emissions

Reducing methane emissions and water use is critical for combating climate change and declining aquifers on food production. Reductions in irrigation water use and methane emissions are known benefits of practicing alternate wetting and drying (AWD) over continuous flooding (CF) water management in lowland rice (Oryza sativa L.) production systems. In a two-year (2020 and 2021) study, methane emissions from large farm-scale (∼50 ha) rice fields managed under CF and AWD in soils dominated by Sharkey clay (Sharkey clay, clay over loamy, montmorillonitic non-acid, thermic Vertic halauepet) were monitored using the eddy covariance method (EC). In the EC system, an open-path laser gas analyzer was used to monitor air methane gas density in the constant flux layer of the atmosphere over the rice-crop canopies. Total water pumped into the field for floodwater management was higher in CF compared to AWD by 24 and 14% in 2020 and 2021, respectively. Considerable variations between seasons in the amount of methane emitted from the CF and AWD treatments were observed: CF emitted 29 and 75 kg ha−1 and AWD emitted 14 and 34 kg ha−1 methane in 2020 and 2021, respectively. Notwithstanding, the extent of reduction in methane emissions due to AWD over CF was similar for each crop season (52% in 2020 and 55% in 2021). Rice grain yield harvested differed by only ±2% between AWD and CF. This investigation of large-scale system-level evaluation, using the EC method, confirmed that by practicing AWD floodwater management in rice, water pumped from aquifers could be reduced by about a quarter and methane emissions from rice fields could be cut down by about half without affecting grain yields, thereby promoting sustainable water management and greenhouse gas emission reduction during rice production in the Lower Mississippi Delta.

Changes in the activities of key enzymes and the abundance of functional genes involved in nitrogen transformation in rice rhizosphere soil under different aerated conditions

Soil microorganisms play important roles in nitrogen transformation. The aim of this study was to characterize changes in the activity of nitrogen transformation enzymes and the abundance of nitrogen function genes in rhizosphere soil aerated using three different methods (continuous flooding (CF), continuous flooding and aeration (CFA), and alternate wetting and drying (AWD)). The abundances of amoA ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB), nirS, nirK, and nifH genes; and the activities of urease, protease, ammonia oxidase, nitrate reductase, and nitrite reductase were measured at the tillering (S1), heading (S2), and ripening (S3) stages. We analyzed the relationships of the aforementioned microbial activity indices, in addition to soil microbial biomass carbon (MBC) and soil microbial biomass nitrogen (MBN), with the concentration of soil nitrate and ammonium nitrogen. The abundance of nitrogen function genes and the activities of nitrogen invertase in rice rhizosphere soil were higher at S2 compared with S1 and S3 in all treatments. AWD and CFA increased the abundance of amoA and nifH genes, and the activities of urease, protease, and ammonia oxidase, and decreased the abundance of nirS and nirK genes and the activities of nitrate reductase and nitrite reductase, with the effect of AWD being particularly strong. During the entire growth period, the mean abundances of the AOA amoA, AOB amoA, and nifH genes were 2.9, 5.8, and 3.0 higher in the AWD treatment than in the CF treatment, respectively, and the activities of urease, protease, and ammonia oxidase were 1.1, 0.5, and 0.7 higher in the AWD treatment than in the CF treatment, respectively. The abundances of the nirS and nirK genes, and the activities of nitrate reductase and nitrite reductase were 73.6, 84.8, 10.3 and 36.5% lower in the AWD treatment than in the CF treatment, respectively. The abundances of the AOA amoA, AOB amoA, and nifH genes were significantly and positively correlated with the activities of urease, protease, and ammonia oxidase, and the abundances of the nirS and nirK genes were significantly positively correlated with the activities of nitrate reductase. All the above indicators were positively correlated with soil MBC and MBN. In sum, microbial activity related to nitrogen transformation in rice rhizosphere soil was highest at S2. Aeration can effectively increase the activity of most nitrogen-converting microorganisms and MBN, and thus promote soil nitrogen transformation.

Evaluating the Suitability of System of Rice Intensification Practices for Enhancing Rice and Water Productivity in Semi-Arid Environment, Tamil Nadu, India


 In the world of rapid change in climate, irregular rainfall pattern tends to pose serious impact on water availability for agriculture. Rice is one of the important food crops to get affected by the low water availability because of its high water requirement. Various techniques were used in the past to mitigate low water availability and increase productivity but most techniques will improve one aspect at the expense of the other. System of Rice Intensification (SRI) is being tried by many countries with several modifications based on their priorities, with the aim of enhancing productivity besides reducing the water demand for rice cultivation. It is essential to have more insight into the individual and compounding effect of multiple components of SRI on yield, and water productivity of rice for identifying the potential and suitable SRI practices. Investigating the influence of different practices of SRI viz., planting of young and single seedlings per hill in wider spacing, water saving irrigation like Alternate Wetting and Drying (AWD), and weed control using cono-weeders on rice using the data obtained from the field experiment carried out during 2021 in Tamil Nadu Agricultural University, Coimbatore, India. Water productivity of rice plants under SRI were compared with conventional practices. The results revealed that plants grown with complete SRI practices had increased water productivity by 0.25 kg grain/m3 of water which is almost twice that of conventional cultivation system. The yield obtained in SRI treatments was higher about 39% than conventional treatments. The total water savings were 20 % higher in AWD treatments than continuous flooding treatments.
 

Integrated effects of microbial decomposing inoculant on greenhouse gas emissions, grain yield and economic profit from paddy fields under different water regimes

Few studies have comprehensively evaluated the impacts of microbial decomposing inoculants on greenhouse gas emissions and economic profit from paddy fields under different water regimes. Here, this study evaluated the effects of microbial decomposing inoculant treatments (straw returning without or with microbial decomposing inoculants (S and SMD)) on rice yield, CH4 and N2O emissions, economic profit and net ecosystem economic profit (NEEP) from paddy fields under different water regimes (continuous flooding (CF) and alternate wetting and drying irrigation (AWD)) in central China with a two-year field experiment. Compared with S treatment, SMD treatment significantly increased the rice yield and crop water productivity by 6.6–7.2% and 5.6–7.9%, respectively. AWD treatment significantly enhanced the crop water productivity by 56.9–73.7% while did not affect rice yield relative to CF treatment. Regardless of water regimes, SMD treatment did not affect N2O emissions, but significantly increased CH4 emissions by 13.8–39.6% relative to S treatment, resulting in a remarkable enhancement of global warming potential by 13.5–32.5%. Compared with S treatment, SMD treatment improved the economic profit and NEEP. By contrast, AWD treatment significantly increased N2O emissions by 19.1–64.8% compared with CF treatment, but significantly reduced CH4 emissions by 35.3–79.1%. Accordingly, AWD treatment significantly decreased the global warming potential by 33.4–73.9% compared with CF treatment. In addition, AWD treatment resulted in 39.9–96.4% higher economic profit and 48.0–124.4% higher NEEP relative to CF treatment. In summary, AWD treatment is a sustainable water regime that can maintain rice yield, mitigate global warming potential, and increase economic income. However, regardless of water regimes, SMD treatment led to higher rice yield and economic profit, as well as higher global warming potential than S treatment, suggesting that other appropriate treatments of crop straw are needed to mitigate CH4 emissions while improving economic profit for rice sustainable production.

Characteristics of Paddy Soil Organic Carbon Mineralization and Influencing Factors Under Different Water Conditions and Microbial Biomass Levels

Paddy soil often undergoes frequent dry-wet alternation. The change in water status not only affects the physical and chemical properties of the soil, but also changes the structure and diversity of the soil microbial communities, which in turn determines the rate of soil organic carbon mineralization. However, the effects of different water conditions and soil microbial biomass levels on the process of soil organic carbon mineralization and its mechanisms are still unclear. Therefore, this study took typical subtropical paddy soil as the research object, applied a laboratory incubation experiment with two water treatments of dry-wet and continuous flooding, and reduced the soil microbial biomass through chloroform fumigation, thereby obtaining high and low soil microbial biomass carbon contents, to elucidate the influencing mechanisms of microbial biomass and water conditions on organic carbon mineralization in paddy soil. The results showed that during the first 30 d of incubation, the dry-wet treatment was in a non-flooded stage and its cumulative CO2 emissions were significantly lower than those of the continuous flooded treatment. After 30 d, the dry-wet treatment entered the flooded stage. The difference in the cumulative CO2 emissions of the soils with a high microbial biomass carbon content between the dry-wet and continuous flooding treatments gradually decreased, and there was no significant difference on day 78. In the soil with a low microbial biomass carbon content, the cumulative CO2 emissions of the dry-wet treatment on day 78 was still significantly lower than that of the continuous flooded treatment. The soils with a low microbial biomass carbon content showed a faster CO2 emission rate at the beginning of the incubation period (first 20 d), which was 1.1-6.1 times greater than that of the high microbial biomass carbon soils owing to their high soil dissolved organic carbon (DOC) content, and the CO2 emission rate then gradually decreased until it was below that of the soil with a high microbial biomass carbon content. The soil organic carbon mineralization rate became stable later in the incubation period (days 45-78). The stable mineralization rate of the high microbial biomass carbon soil was 20%-30% higher than that of the low microbial biomass carbon soil. The multiple regression analysis results showed that the decrease in the soil DOC content (ΔDOC) and the increase in the Fe2+ content (ΔFe2+) significantly affected the change in cumulative CO2 emissions (ΔCO2) under continuous flooding conditions, but had no effect on ΔCO2 during the flooding stage of the dry-wet treatment. The correlation analysis showed that the daily CO2 emission rate of soils with high microbial biomass carbon was significantly positively correlated with glucosidase activity under dry-wet treatment and significantly negatively correlated with acetylglucosaminidase (NAG) and peroxidase activities under continuous flooding treatment. In the low microbial biomass carbon soils, the daily CO2 emission rate of the continuous flooding treatment was negatively correlated with the NAG activity, but showed no correlation with enzyme activities under dry-wet management. In summary, the cumulative CO2 emissions of dry-wet treatment were lower than those of continuous flooding treatment, and the difference was significant in soils with low microbial biomass carbon. The size of the soil microbial biomass determined the level of the stable soil organic carbon mineralization rate. The amount of soluble organic carbon and iron reduction affected the soil CO2 emissions under continuous flooding conditions, and the soil water conditions affected the daily CO2 emission rate and its key influencing enzymes. This study provides data and theoretical support for the carbon cycle and carbon sequestration potential in paddy soil.

Control of paddy soil redox condition on gross and net ammonium fixation and defixation

Abiotic fixation and defixation of ammonium (NH4+) in silicate interlayers are common processes in paddy soils, owing to their often high levels of 2:1 type clay minerals. Fixed NH4+ hence forms a buffer during the supply and loss of plant-available N. The soil redox potential (Eh) is suspected to influence NH4+ (de)fixation by its impact on the negative charge of Fe3+-containing clay minerals, yet experimental confirmations are scarce. We examined the effect of a fluctuating or generally increased Eh on dynamics of NH4+ (de)fixation in a Bangladeshi paddy soil (total N: 1.9 g kg−1 | CEC: 43 cmol kg−1) during two incubation experiments. In those, we either 15N-labelled the fixed NH4+ pool (with initially 87 mg kg−1 exchangeable versus 393 mg kg−1 fixed NH4+-N) or the exchangeable pool (with initially 141 mg kg−1 exchangeable versus 249 mg kg−1 fixed NH4+-N), and this under three Eh-controlling treatments: continuous flooding (CF), CF with extra MnO2 added (3.5 g kg−1 Mn4+) (CF-MnO2), and alternate wetting and drying (AWD). The CF treatment overall led to somewhat higher net NH4+ fixation than AWD and, less clearly, also compared to the CF-MnO2 treatment, resulting from higher gross NH4+ fixation as well as lower gross defixation. These fluxes always led to a dynamic equilibrium between the exchangeable and fixed NH4+ pool within a few days of incubation, and this equilibrium was the same for both experiments but depended on the Eh treatment. However, by altering other NH4+ transformation processes, Eh treatments also indirectly impacted NH4+ (de)fixation fluxes, for which the equilibrium ratio between exchangeable versus fixed NH4+ turns out to be the determining factor.

Effect of Water Management on Rice Growth and Rhizosphere Priming Effect in Paddy Soils

The rhizosphere priming effect (RPE) caused by carbon inputs from crop rhizodeposits plays a key role in regulating the carbon emission flux and carbon balance of farmland soils. Due to frequent alternations between dry and wet conditions, CO2 and CH4 emissions and the RPE in paddy field ecosystems are significantly different to those of other ecosystems. Therefore, it is of great significance to determine the direction and intensity of the rice RPE under alternations of dry and wet to limit greenhouse gas emissions. In this study, using a 13C-CO2 continuous labeling method combined with a pot-based experiment, the response of rice growth and the RPE under alternating dry and wet and continuous flooding conditions was examined. The results showed that, compared with the continuous flooding treatment, the alternating dry and wet treatments significantly increased aboveground and root biomass and the root-to-root ratio, and also increased soil microbial biomass. Under continuous flooding conditions, fluxes of 13CO2 and 13CH4 increased with rice growth from 10.2 μg·(kg·h)-1 and 2.8 μg·(kg·h)-1 (63 d) to 16.0 μg·(kg·h)-1 and 3.2 μg·(kg·h)-1 (75 d), respectively. During the 12-day drying process, the emissions of 13CO2 and 13CH4 derived from rhizosphere deposited C decreased by 57.5% and 88.1%. Under continuous flooding conditions, the RPE for CO2 and CH4 were positive and increased with the growth of rice. Under the alternating dry and wet treatment, after 12 days of drying, the RPE for CO2 and CH4 was reduced from 0.29 mg·(kg·h)-1 and 12.3 μg·(kg·h)-1 (63 d) to -0.39 mg·(kg·h)-1 and 0.07 μg·(kg·h)-1 (75 d). Thus, alternating wet and dry treatment can effectively promote rice growth and reduce the cumulative emissions of CH4. Therefore, adopting appropriate field water management is of great significance for increasing rice yields and mitigating greenhouse gas emissions.

Alternate Wetting and Drying (AWD) in Broadcast rice (Oryza sativa L.) Management to Maintain Yield, Conserve Water, and Reduce Gas Emissions in Thailand

In Thailand, rice production accounts for the largest proportion of irrigated crop production, especially in the dry season. Water shortage problems have recently become widespread in Thailand, with implications for irrigated rice cultivation. Compared with the continuous flooding (CF) technique, the alternate wetting and drying (AWD) technique can reduce the amount of water typically needed in rice systems and can reduce methane emissions produced from paddy fields. In this study, AWD (10/-10, 10/-15, and 10/-20) and CF combined with the broadcasting technique were studied at seven rice research stations in the dry seasons of 2014 and 2015. The results showed that the AWD technique reduced grain yields compared with those of CF, but the milling quality was not significantly different among the treatments. In addition, the total CH4 emissions from the AWD treatments were less than those from CF, but the percentage of CH4 reduction in the AWD treatments was different among the seven stations. However, the total N2O emissions were not significantly different between the CF and AWD treatments. Thus, if water scarcity is happening and if it is necessary to grow rice in those cases, the AWD10/-10 technique is recommended in broadcast rice systems in Thailand.

Response of Root-Exuded Organic Acids in Irrigated Rice to Different Water Management Practices

Knowledge of the composition and volume of root-exuded organic substances is crucial for understanding the biochemical processes in the rhizosphere. The present study was undertaken to quantify organic acids from the roots of drought-tolerant and non-drought-tolerant rice cultivars (DTR and NDTR) and their response to irrigation during different growth periods. Alternating wetting and moderate drying with 4 cm water layer of flood irrigation until the soil water potential reaches −15 kilopascal (kPa) (WMD) significantly enhanced succinic, maleic, citric, malic, oxalic, tartaric, and total organic acids in the two rice cultivars during the trial by 80.59–86.68, 31.62–58.55, 16.55–43.00, 17.89–25.66, 13.68–29.70, 12.40–16.05, and 17.34–21.24%, respectively. Alternate wetting and severe drying with 4 cm water layer of irrigation until the soil water potential reached −30 kPa (WSD) notably decreased formation of maleic, citric, malic, oxalic, tartaric, and total organic acids in the two rice cultivars during the experiment by 5.19–25.15, 13.96–29.92, 20.81–34.88, 32.20–42.51, 12.79–24.66, and 6.67–24.22%, respectively. Acetic acid output between CF (continuous flooding with a 3–4 cm water layer) and WMD treatments in pads with two rice cultivars did not differ. The WSD treatment increased acetic acid exudation by 16.93–25.99% in two rice cultivars during the experiment. The high content of acetic and total organic acids in DTR should be responsible for the smaller loss of total organic acids in the WSD treatment and the high drought tolerance capacity. The results contribute to valuable background knowledge for exploring the role of root exudates in soil-plant relationships.

Simulating water productivity of paddy rice under irrigation regimes using AquaCrop model in humid and semiarid regions of Iran

Rice production in the world is heavily dependent on water. Therefore, increasing in water productivity with appropriate irrigation management is necessary. Simulation models that illustrate the effects of water on crop growth can apply to optimize water productivity and improve farm irrigation management. This study was conducted to simulate water productivity of paddy rice using AquaCrop model in both humid and semiarid regions of Iran. Required data for running model were gained from two field experiments: an experiment with a lowland local rice cultivar named Champa-Kamfiroozi in a semiarid climate (Kooshkak), and other experiment with two lowland local rice cultivars named Binam and Hasani in a humid climate (Rasht). Both experiments were conducted under five irrigation treatments in two consecutive years. As a result, the relative root mean square error (RRMSE) of grain yield simulation was gained between 2.28 and 15.09%. The ranges of water productivity based on transpiration (WPT) and water productivity based on evapotranspiration (WPET) as affected by irrigation treatments, in dry climate were greater than wet climate. The averages of WPT and WPET for continuous flooding in the humid (1.21 and 0.82 kg m−3, respectively) and dry (1.26 and 0.76 kg m−3, respectively) climates showed the role of evaporation losses in decreasing WP in dry climate. The highest ET was obtained in continuous flooding treatments that the amount of evaporation for dry climate was 88% higher than humid climate.

Prediction of the uptake of Cd by rice (Oryza sativa) in paddy soils by a multi-surface model

The uptake of Cd by crops from soils is predominantly determined by the concentration and speciation of Cd in soil solution, which is controlled by soil physicochemical properties such as soil pH, soil minerals and organic matter, etc. Water management significantly affects soil pH, and especially soil pH is driven to be neutral under continuous flooding treatment. In the present study, the multi-surface models (MSMs) were modified to determine Cd partitioning in soils for prediction of Cd uptake by rice grain, with multiple parameter or setup changes including: (1) soil pH was considered as variables to improve the accuracy of model prediction for paddy soils; (2) practical co-existing cation concentration and ionic strength were derived from electron conductivity to improve the universality of model. Our results suggested that the modified MSMs model provided a better prediction for the actual uptake by rice grain and a more consistent Cd distribution pattern in paddy soils.

벼 논에서 양수분 복합관리에 따른 온실가스 (CH4, N2O) 배출 특성 및 수량 변동에 미치는 영향

Intermittent drainage can be used to reduce methane (CH₄) emission from paddy soils. However, there is a significant increase in nitrous oxide (N₂O) emission when this water is drained, a significant amount of which originates from N fertilizer. Therefore, to mitigate the side effects of drainage, the source of N fertilizer should be considered. However, water and nutrient management effects during rice cultivation are not well examined in Korea. In this study, effects of water and nutrient management on reducing greenhouse gas (GHG) emissions were investigated in a rice paddy. Three types of water management were conducted: Continuous flooding (CF), intermittent drainage (ID), and low level water management (LL). At 30 days after rice transplant, drainage was carried out for 20 days in the ID treatment, and a low level of water (2~5cm) was maintained in LL treatment. The same amount of fertilizer (N‐ P₂OSUB5/SUB‐K2O:110‐45‐57 kg ha‐1) was applied in each treatment group, but different types of N sources were used: Urea (NPK), hairy vetch with urea (HV), and slow release fertilizer in the form of latex‐coated urea (SRF). To prevent N deficiency in HV treatment, 50% of the N fertilizer was replaced with urea as additional fertilizer. Methane and N₂O emissions were monitored during rice cultivation, as were growth properties and rice yield. Compared with CF treatment, ID and LL showed significantly decreased CH₄ emission. Despite organic matter application, CH₄ emission was lower in the LL+HV and ID+HV treatments than in the CF+NPK treatment. On the contrary, N₂O emission was increased in ID and LL treatments. However, due to the CH₄ reduction effect, global warming potential (GWP) was decreased in ID and LL treatments. Rice yield was slightly higher in the SRF than NPK treatment. As a result, yield‐scaled greenhouse gas intensity (GHGI) was decreased in water and nutrient managed fields due to the low GWP and high yield. Conclusively, a combination of water and nutrient management might reduce GHG emissions in rice paddies without loss of yield. In particular, low level water management and slow release fertilizer application were effective to reduce CH₄ and N₂O emissions and increase rice yield.

Water management of alternate wetting and drying reduces the accumulation of arsenic in brown rice - as dynamic study from rhizosphere soil to rice

There have been no controlled systematic studies on the dynamic variation of As in soil - soil porewater - root surface (Fe plaques) - rice plant system under alternate wetting and drying (AWD) irrigation. Therefore, effects of continuous flooding (CF) and AWD treatments (2F2D: 2-day flooding followed by 2-day drying; 7F2D: 7-day flooding followed by 2-day drying) on the migration of As from soil to brown rice were studied. Results indicated that As contents in brown rice of AWD treatments (0.03–0.17 mg/kg) were 43.3%–85.0% lower than CF (0.20–0.30 mg/kg). AWD irrigation promoted the transformation of Fe and associated As in rhizosphere soil from highly active forms (H2O and HCl-extracted Fe-bound As) to stable states (oxalate and DCB-extracted Fe-bound As), which decreased the release of As from rhizosphere soil. The dynamic variation of As contents in porewater was described by a dissolution factor (DF) which decreased significantly in AWD treatments and had a significant positive correlation (R2 = 0.83; P < 0.05) with As contents in brown rice. In addition, contents of Fe and associated As on the root surface were about 17.1% and 11.0% higher in AWD treatments than in CF treatment, respectively, and the transfer factor (TF) of As from root surface into root was 22.7% lower in AWD treatments than in CF. In summary, AWD irrigation reduced As contents in porewater through decreasing availability of As in rhizosphere soil; and AWD also reduced the transfer of As into rice roots through promoting As sequestration by Fe plaques on root surface.

Yield Response and Water Productivity for Rice Growth With Several Irrigations Treatment in West Java

As the challenges toward increasing water for irrigation and water scarcity threats become more prevalent, knowledge of crop yield response to water can facilitate the development of irrigation strategies for improving agricultural productivity. Experiments were conducted to to compare water usage of several irrigation treatment on rice growth performance and productivity and its water use efficiency. These experiments were conducted using Situbagendit rice variety (115 day length periode), Urea and Tri Super Phospate fertilizer. Fertilizer dosage follows fertilizer recommendations for rice, i.e : Urea 250 kg/ha, SP-36 100 kg/ha and 100 kg KCl/ha. Irrigation started from land preparation. controll block (deep flooding) was flooded by a water height of 7 cm. Low level continues flow block was flooded by a water height of 3-5 cm. The volume of water used to saturate the soil of the saturated block was estimated. The number of days of non-flooded soil in AWD before irrigation is applied can vary from 1 day to more than 5 days. The results showed that total volume of water supplied during the rice growing period in the control block was 2,761.91 m3. Total water volume related to the low level continous flow irrigation block was about 1,217.03 and only about 638.98 m3 for the alternate wet and dry irrigation block. Total volume supplied for soil saturation treatment was about 549.74 m3. Regardless the performance of rice crop growth, it’s the most efficient treatment in terms of water use. It only required an amount of water around14-20 % of amount of water consumed by the continuous deep flooding treatment. The rice yield of deep flooding irrigation treatment was equivalent to 5.6 tons/ha of dry paddy while the yields of low level continuous flow irrigation,alternate wet and dry irrigation and soil saturation treatments reached 5,3 tons/ha,3.36 tons/ha and 2.80 tons/ ha respectively

Dynamics of the rice rhizosphere microbial community under continuous and intermittent flooding treatment

Flooding regime is an important agronomic strategy, and widely applied in heavy metal-contaminated soil for controlling heavy metal uptake through biochemical processes. However, the dynamics of the microbial community in the rhizosphere of rice under different flooding systems are not well understood. In the present study, we investigated the dynamics between the microbial community and heavy metal ions under continuous flooding (CF) and intermittent flooding (IF) conditions to decipher the relationship between microbial community and environmental factors. The results showed that, for the complex Cd, Pb, and Zn contaminated soil under CF treatment did not significantly suppress Cd uptake, but promoted Pb and Ni accumulation into the rice root. Soil pH and bio-available phosphate content appeared to be the key factors impacting heavy metal mobility. When observing the microbial community in the rhizosphere, long term flooding resulted in an abundance of Anaeromyxobactersp., Geobacter and Desulfovibrio, and the abundance of these taxa displayed a significant relationship to Pb and Zn content of rice roots. From the study, we observed that the flooding regime could have a significant impact on concentrations of Cd, Pb and Ni in rice roots, and the different richness of SRB and FeRB may contribute to uptake of these heavy metals. In future work, the impact of Fe cycling on heavy metal bioavailability in the plant rhizosphere should be investigated further.

N2O, CH4, and CO2 Emissions from Continuous Flooded, Wet, and Flooded Converted to Wet Soils

Fluctuations in soil water content, either anthropogenic or natural, can remarkably influence the C and N pools in arable lands. The dynamics of C and N are directly related in regulation of greenhouse gases (GHGs) emissions. The present study was conducted to explore the effects of water regimes (continuous flooding, continuous wet, and flooding converted to wet) on soil GHGs emissions. Nitrous oxide (N2O) emissions from continuous flooding treatment were lower as compared with the continuous wet soil, but significantly (p ≤ 0.01) enlarged in the flooding converted to wet soil treatment through increased mineral nitrogen. Methane (CH4) emissions were significantly (p ≤ 0.01) higher in the continuous flooding when compared with the wet soil conditions but substantially decreased in the flooding converted to wet soil treatment. Carbon dioxide (CO2) emissions were significantly (p ≤ 0.01) larger in the flooding converted to wet soil treatment as compared with the continuous flooding and wet soil treatments owing to increased mineralization and C contents. The results suggest that converting flooding to wet soil can substantially triggers the C and N pools and thus influences the GHGs emissions from soil.