Alternate Wetting And Drying Treatments Research Articles

Effect of Alternate Wetting and Drying on the Emission of Greenhouse Gases from Rice Fields on the Northern Coast of Peru

The cultivation of rice is one of the main sources of greenhouse gas (GHG) emissions due to continuously flooded irrigation (CF), which demands large volumes of water. As an alternative solution, alternate wetting and drying (AWD) irrigation has been developed as a water-saving strategy. This study was conducted at the Experimental Agricultural Station (EEA) in Vista, Florida, in the Lambayeque region located on the northern coast of Peru. Thus, it was analyzed the effect of AWD irrigation at different depths (5, 10, and less than 20 cm below the surface) compared to CF control on methane (CH4) and nitrous oxide (N2O) emissions and rice grain yield. AWD treatments reduced CH4 emissions by 84% to 99% but increased N2O emissions by 66% to 273%. In terms of Global Warming Potential (GWP), the AWD10 treatment demonstrated a 77% reduction and a Water Use Efficiency (WUE) of 0.96, affecting only a 2% decrease in rice grain yield, which ranged between 11.85 and 14.01 t ha−1. Likewise, this study provides sufficient evidence for the adoption of AWD irrigation as a strategy for the efficient use of water resources and the mitigation of GHG emissions in rice cultivation in the study area, compared to continuous flooded irrigation.

Evaluating greenhouse gas mitigation through alternate wetting and drying irrigation in Colombian rice production

Rice demand in Latin America is increasing rapidly, but few studies have identified management practices to reduce water demand and soil greenhouse gas (GHG) emissions for irrigated rice systems in this region. Therefore, we tested the hypothesis that alternate wetting and drying (AWD) irrigation could maintain crop yields while mitigating global warming potential (GWP) compared to a conventional system with recommended irrigation and nutrient management practices for tropical rice in Colombia. Over four consecutive growing seasons, we monitored CH4 and N2O emissions, grain yield, and water consumption for two AWD treatments (AWD5 cm and AWD10 cm - where water drained to depths of 5 and 10 cm below the soil surface, respectively) and a control, in which the field was drained multiple times during fertilizer applications and then continuously flooded until harvest. The control had the highest water use across all rice seasons, with values ranging from 9260 to 16559 m3 ha−1 harvest−1. Implementation of AWD reduced cumulative water use by 19–56%, especially in dry seasons. Both AWD treatments significantly reduced cumulative CH4 emissions by 72–100%, which is consistent with previous research. A new finding is that AWD also decreased N2O emissions by 12–70%, which was attributed to management of soil moisture during fertilizer application events. In total, AWD reduced GWP by 25–73% compared to the control, with minimal impacts on crop productivity. Rice yields ranged from 5.2 to 8.2 Mg ha−1, with no significant difference among treatments in three of four seasons. This study shows that AWD saves irrigation water while greatly reducing GWP with little agronomic penalty, suggesting this technology could be a promising strategy for GHG mitigation in tropical rice in Colombia. Because there are important barriers to AWD adoption, future work should explore challenges at the farm-level as well as changes in policy, irrigation infrastructure, and institutional arrangements to understand the potential for broader implementation.

Development and evaluation of the first automated irrigation system for alternate wetting and drying technique in rice cultivation in Bangladesh

Rice stands as one of the most water-intensive crops in agriculture, demanding a substantial volume of water annually for cultivation in Bangladesh. To address this considerable water requirement, the International Rice Research Institute (IRRI) introduced the alternate wetting and drying (AWD) irrigation method. This approach necessitates consistent manual oversight to maintain the desired water levels in the field. In pursuit of reducing this manual effort, a study was conducted at Bangabandhu Sheikh Mujibur Rahman Agricultural University. The study aimed to develop an automated version of the AWD irrigation system, assess its impact on plant growth and yield-contributing factors, and investigate water use efficiency through using that automated system. The automated AWD system incorporated water level controllers, solenoid valves, and water level detection probes to regulate water levels in the paddy field. The experiment followed a Randomized Complete Block Design (RCBD) with three treatments: T1 (Conventional Irrigation - CI), T2 (AWD), and T3 (Automated Alternate Wetting and Drying - AAWD), each replicated four times. The findings indicated minimal variation in growth and development parameters of the rice plants between the CI and AWD treatments. Likewise, yield components demonstrated no significant differences among the various treatments. Notably, the treatment with automated alternate wetting and drying (AAWD), namely T3, displayed the highest water use efficiency (WUE) at 65.20 kg/ha/cm, while the lowest WUE of 52.56 kg/ha/cm was observed in the conventional irrigation (CI) treatment T1. The results underscore the clear advantage of adopting an automated AWD system, yielding a 20% reduction in irrigation water usage compared to the conventional approach. This transition also minimizes the need for labor-intensive interventions in the paddy fields of Bangladesh, illustrating the potential for more efficient and sustainable rice cultivation practices.

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.

Elevated CO2 enhances rice root growth under alternate wetting and drying irrigation by involving ABA response: Evidence from the seedling stage

AbstractThe atmospheric CO2 enrichment can seriously affect rice root growth. Alternate wetting and drying (AWD) irrigation, which can also increase root growth, is a widely promoted water‐saving technology for future climate, yet how elevated CO2 (eCO2) influences rice root growth under AWD remains unclear. In the present study, we examined the root growth of Yangdao 6 (YD 6) and Koshihikari (KOS) cultured under different water irrigation regimes (well‐watered and AWD) and CO2 concentration (400 and 800 ppm). AWD reduced shoot dry weight of KOS compared with WW under ambient CO2 (400 ppm, aCO2), while the shoot dry weight of KOS showed no difference between WW and AWD treatments under eCO2. Additional, under aCO2, AWD did not affect the exhibited similar root dry weight, length, total surface area, and volume of YD 6 and KOS relative to WW. However, under eCO2, AWD significantly promoted the root dry weight, root length, total root surface area, and root volume of YD 6 and KOS. Furthermore, root ABA content of YD 6 and KOS was significantly higher under AWD than under WW. Then, the OsNCED3 (a key gene for ABA biosynthesis) RNAi lines were used to check the role of ABA in root growth under eCO2 with AWD conditions. The results showed that AWD increased the ABA content and root parameters of WT but not the OsNCED3 RNAi lines under eCO2. Overall, the results suggest that eCO2 can improve rice root growth under AWD by involving root ABA, which contributes to the understanding of water‐saving irrigation on rice in the future climate.

Performance of different conservation practices for irrigated paddy rice (Oryza sativa) cultivation as affected by soil texture of Mymensingh region in Bangladesh

Soil moisture is critical to the growth and yield-contributing character traits of rice. However, few studies have yet to outline the effects of soil texture on irrigated paddy rice cultivation under diverse conservation techniques. In this regard, an experiment was conducted at the Field Irrigation Laboratory of Bangladesh Agricultural University to investigate the water productivity and yield-contributing characteristics of paddy rice (Oryza sativa L.; variety: BRRI dhan 28) during Boro season for two years with two different soil textures (silt loam, 2019 and loam, 2020) and three different irrigation techniques, namely, Alternate Wetting and Drying (AWD), Raised Bed (RB) and the conventional Continuous Flooding (CF). It was observed that seepage in CF treatment was higher than that of AWD and RB. Highest grain yield (6.70±0.04 t/ha) was found for 15 cm AWD treatment (irrigation applied when water level reached 15 cm below ground surface) for silt loam and the same for loam soil was 6.53±0.50 t/ha under 10 cm AWD treatment. CF method of irrigation yielded grain lowest for both silt loam (5.47±0.05) t/ha and loam (5.28±0.19) t/ha soil. For both soil textures, CF treatment required more water than conservation treatments and resulted in lower water productivity. Again, for both the types of soil, AWD performed comparatively better than the CF, especially 15 cm AWD for silt loam soil and 10 cm AWD for loam soil because it required minimum water for paddy rice cultivation and its water productivity was maximum for the same rice production. Therefore, adopting these water-conserving methods would have a considerable implication for water-scarce agricultural regions.

Alternate wetting and drying modulated physio-biochemical attributes, grain yield, quality, and aroma volatile in fragrant rice.

Alternate wetting and drying (AWD) has been recognized as a water-saving technology in rice production systems; however, pre- and post-flowering AWD could induce changes in yield, quality and aroma biosynthesis in fragrant rice. In the present study, two fragrant rice cultivars (Guixiangzhan and Nongxiang-18) were subjected to AWD till soil water potential reached -25 to -30 kPa during vegetative stage (VS), reproductive stage (RS), and both stages (VS + RS). The AWD did not affect net photosynthesis and gas exchange significantly, while malondialdehyde (MDA), H2 O2 and electrolyte leakage (EL) were higher than in control plants. The AWD treatments variably affected soluble sugars, proline and protein accumulation as well as the activities of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), ascorbate peroxidase (APX), and reduced glutathione (GSH) contents. Moreover, filled grain percentage and 1000-grain weight in AWD treatments were found to be statistically similar (p > 0.05) to control, except grains panicle-1 under AWD-VS + RS that was reduced by 11% and 14% for Guixiangzhan and Nongxiang-18, respectively. On average, yield and related attributes in Guixiangzhan remained higher than in Nongxiang-18. In addition, the grain aroma volatile (2-acetyl-1-pyrroline, 2-AP) content increased by 8.79%, 14.45%, and 6.87% and 7.95%, 14.02%, and 5.04% under AWD-VS, AWD-RS, and AWD-VS + RS treatments, for Guixiangzhan and Nongxiang-18, respectively. Overall, AWD treatments, either at VS or RS, could promote rice aroma in terms of accumulation of 2AP, which might be linked with enhanced endogenous proline contents (a precursor for 2AP biosynthesis) without any severe consequences on rice yield and quality.

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.
 

Effects of Different Irrigation Management on the Textural Properties of Double-Cropping Late Indica Rice in South China

In order to investigate the effects of different irrigation management on the textural properties of two different double-cropping late <i>Indica</i> rice, the effects of three irrigation management including conventional irrigation (CK), constant irrigation (CI) and alternate wetting and drying (AWD) on textural properties has been researched under field conditions of two years. The results indicated that the firmness, cohesiveness and chewiness were decreased under AWD treatment, and the stickiness was increased compared with CK, while the textural properties under CI treatment showed the opposite trend with AWD treatment. Additionally, AWD treatment signifi- cantly improved the springiness of TY871 compared with CK and CI treatment, but had no significant effect in RYHZ, suggesting improvement of the cooking and eating quality of TY871 under AWD treatment. Correlation analysis showed that the chewiness was positively correlated with the firmness and cohesiveness, and the cohesiveness was positively correlated with the firmness. AWD could promote the textural properties of high-quality late <i>Indica</i> rice in South China whereas CI treatment has shown the disadvantage of the textural properties, which will provide useful information for the improvement of cooking and eating quality of rice.

Translocation of Soil Arsenic towards Accumulation in Rice: Magnitude of Water Management to Minimize Health Risk

Globally, the risk of arsenic (As) contamination in soil and rice is well documented across the globe. In Bangladesh, drinking water and rice are two major exposure pathways of As to humans. Therefore, the efficiency of recent technologies to reduce rice As and associated human health risks still need to be deeply investigated. In this direction, a pot experiment was performed to investigate the impact of soil As and agronomic irrigation management on rice (cv. BRRI dhan28) growth, yield, As accumulation, and finally, health risks to humans from consuming rice. Treatment combinations were made with three levels of As (0, 20, and 40 mg kg−1) having two irrigation procedures, including alternate wetting and drying (AWD) and traditional continuous flooding (CF). According to the findings, As pollution in the soil lowered the yield contributing features and rice yield, including panicle length, filled grains per panicle, sterile grains per panicle, 1000-grain weight, grain yield, and straw yield. AWD water management significantly improved the growth performance and productivity of rice. Grain yield was increased by 13% in AWD compared to CF. Rice grain and straw As concentrations were increased to 0.56 mg kg−1 and 15.10 mg kg−1, respectively, in soil with 40 mg kg−1 As and CF water management. AWD treatment significantly reduced grain and straw As contents by 16% and 28%, respectively. Increased grain, straw, and total As uptake was noticed with higher soil As concentrations. The study also found that rising soil As raised non-carcinogenic risks (HQ &gt; 1) and carcinogenic risks (CR &gt; 1.010–4) while AWD lowered health risks compared to CF. Thus, rice farming using AWD irrigation could be a viable and long-term solution for reducing As contamination in rice and associated human health hazards.

Drought-resistance rice variety with water-saving management reduces greenhouse gas emissions from paddies while maintaining rice yields

Rice paddies are a major anthropogenic source of greenhouse gas (GHG) emissions due to the flooding management. Water saving practices often reduce the GHG emissions from rice paddies, yet increase the risk of rice yields loss due to drought stress. Water-saving and drought-resistance rice (WDR) has high drought-tolerant, suggesting that WDR with water-saving management could reduce GHG emissions while maintaining rice yields. However, the effect of WDR on GHG emissions is still unclear. Therefore, we conducted a 2-yr field experiment to assess the effect of WDR on rice yields and GHG emissions under continuous flooding (F), alternate wetting and drying (AWD), and dry cultivation (D) conditions, using a WDR variety and a common variety. Compared to the common variety, the WDR did not affect the rice yields under F and AWD treatments, but increased rice yields by 24% under D treatment. The methane (CH4) emissions and nitrous oxide (N2O) emissions of the two rice varieties were similar. Compared to the F treatment, AWD treatment reduced CH4 emissions by 7%−64% and area-scaled global warming potential (GWP) by 9%−39% and D treatment reduced CH4 emissions by 70%−90% and area-scaled GWP by 65%−74%. The WDR with dry cultivation (D-WDR mode) had the lowest area- and yield-scaled GWP. Our findings indicate that it is possible to produce optimal rice yields with low GHG emissions in the D-WDR mode, and suggest that drought-resistance rice variety breeding may benefit climate change mitigation and adaptation efforts.

Water management of alternate wetting and drying combined with phosphate application reduced lead and arsenic accumulation in rice

Lead (Pb) and arsenic (As) exist in soil with different ionic forms, and it is difficult to immobilize simultaneously Pb and As in soil. The objective of this study is to determine the effects of water management including flooding (FL), alternate wetting and drying (AWD) and dry farming (DF) combined with addition of phosphate (P) on the accumulation of Pb and As in rice. Our results showed that Pb accumulated in root during vegetative stage, and most of As in root was transported to the above ground parts during the reproductive stage. Pb was evenly distributed in grains, and As was mostly accumulated in bran and aleurone layer. Water management had a reverse effect on the accumulation of Pb and As in rice. However, the effects of P on arid soil environment and Pb, As accumulation in rice were stronger than that in flooded soil. Application of P under AWD treatment could maintain a similar quantity of Fe plaque with flooding, decrease the availability of Pb in rhizosphere soil, reduce Pb and As accumulation in root, and result in the reduction of Pb and As accumulation in grains by 86% and 66% respectively. Besides, our study also found that flooding or AWD during vegetative stage facilitated the formation of iron plaque. In conclusion, AWD combined with P application could maintain a relatively lower concentrations of Pb and As in grains.

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.

Field Validation of the DNDC-Rice Model for Methane and Nitrous Oxide Emissions from Double-Cropping Paddy Rice under Different Irrigation Practices in Tamil Nadu, India

Two-year field experiments were conducted at Tamil Nadu Rice Research Institute, Aduthurai, Tamil Nadu, India, to evaluate the effect of continuous flooding (CF) and alternate wetting and drying (AWD) irrigation strategies on rice grain yield and greenhouse gas emissions from double-cropping paddy rice. Field observation results showed that AWD irrigation was found to reduce the total seasonal methane (CH4) emission by 22.3% to 56.2% compared with CF while maintaining rice yield. By using the observed two-year field data, validation of the DNDC-Rice model was conducted for CF and AWD practices. The model overestimated rice grain yield by 24% and 29% in CF and AWD, respectively, averaged over the rice-growing seasons compared to observed values. The simulated seasonal CH4 emissions for CF were 6.4% lower and 4.2% higher than observed values and for AWD were 9.3% and 12.7% lower in the summer and monsoon season, respectively. The relative deviation of simulated seasonal nitrous oxide (N2O) emissions from observed emissions in CF were 27% and −35% and in AWD were 267% and 234% in the summer and monsoon season, respectively. Although the DNDC-Rice model reasonably estimated the total CH4 emission in CF and reproduced the mitigation effect of AWD treatment on CH4 emissions well, the model did not adequately predict the total N2O emission under water-saving irrigation. In terms of global warming potential (GWP), nevertheless there was a good agreement between the simulated and observed values for both CF and AWD irrigations due to smaller contributions of N2O to the GWP compared with that of CH4. This study showed that the DNDC-Rice model could be used for the estimation of CH4 emissions, the primary source of GWP from double-cropping paddy rice under different water management conditions in the tropical regions.

Potential of Alternate Wetting and Drying Irrigation Practices for the Mitigation of GHG Emissions from Rice Fields: Two Cases in Central Luzon (Philippines)

Reducing methane (CH4) emission from paddy rice production is an important target for many Asian countries in order to comply with their climate policy commitments. National greenhouse gas (GHG) inventory approaches like the Tier-2 approach of the Intergovernmental Panel on Climate Change (IPCC) are useful to assess country-scale emissions from the agricultural sector. In paddy rice, alternate wetting and drying (AWD) is a promising and well-studied water management technique which, as shown in experimental studies, can effectively reduce CH4 emissions. However, so far little is known about GHG emission rates under AWD when the technique is fully controlled by farmers. This study assesses CH4 and nitrous oxide (N2O) fluxes under continuous flooded (CF) and AWD treatments for seven subsequent seasons on farmers’ fields in a pumped irrigation system in Central Luzon, Philippines. Under AWD management, CH4 emissions were substantially reduced (73% in dry season (DS), 21% in wet season (WS)). In all treatments, CH4 is the major contributor to the total GHG emission and is, thus, identified as the driving force to the global warming potential (GWP). The contribution of N2O emissions to the GWP was higher in CF than in AWD, however, these only offset 15% of the decrease in CH4 emission and, therefore, did not jeopardize the strong reduction in the GWP. The study proves the feasibility of AWD under farmers’ management as well as the intended mitigation effect. Resulting from this study, it is recommended to incentivize dissemination strategies in order to improve the effectiveness of mitigation initiatives. A comparison of single CH4 emissions to calculated emissions with the IPCC Tier-2 inventory approach identified that, although averaged values showed a sufficient degree of accuracy, fluctuations for single measurement points have high variation which limit the use of the method for field-level assessments.

Rhizosphere Aeration Improves Nitrogen Transformation in Soil, and Nitrogen Absorption and Accumulation in Rice Plants

Two rice cultivars (Xiushui 09 and Chunyou 84) were used to evaluate the effects of various soil oxygen (O2) conditions on soil nitrogen (N) transformation, absorption and accumulation in rice plants. The treatments were continuous flooding (CF), continuous flooding and aeration (CFA), and alternate wetting and drying (AWD). The results showed that the AWD and CFA treatments improved soil N transformation, rice growth, and N absorption and accumulation. Soil NO3– content, nitrification activity and ammonia-oxidising bacteria abundance, leaf area, nitrate reductase activity, and N absorption and accumulation in rice all increased in both cultivars. However, soil microbial biomass carbon and pH did not significantly change during the whole period of rice growth. Correlation analysis revealed a significant positive correlation between the nitrification activity and ammonia-oxidising bacteria abundance, and both of them significantly increased as the total N accumulation in rice increased. Our results indicated that improved soil O2 conditions led to changing soil N cycling and contributed to increases in N absorption and accumulation by rice in paddy fields.

Effect of water-saving irrigation on the N2O dynamics and the contribution of exogenous and endogenous nitrogen to N2O production in paddy soil using 15N tracing

Water-saving irrigation techniques can effectively mitigate methane emissions from rice fields but typically enhance nitrous oxide (N2O) emissions due to changes in soil moisture content. However, few studies have examined the effect of different water regimes on N2O production using different species of exogenous nitrogen (N) fertilizer application. Furthermore, the contributions of exogenous N fertilizer and endogenous N of soil for N2O productions have not been elucidated. Using a series of lysimeters, three types of water management were employed in rice cultivation in this study: conventional irrigation management (CIM), alternate wetting and drying (AWD), and dry cultivation management (DCM). Ammonium nitrate (NH4NO3) fertilizer was applied as base, tillering, and heading fertilizer, which was then separated into two groups labeled with 15N stable isotope (> 99 %) at two different N positions: 15NH4NO3 and NH415NO3.Higher peaks of N2O flux were observed following drainage of floodwater for AWD and DCM treatments. In addition, 15N2O fluxes were clearly separated into two different patterns between 15NO3– and 15NH4+ fertilizer application. Application of 15NO3− fertilizer rapidly released 15N2O but the 15N2O flux for 15NH4+ fertilizer application slowly increased with a hysteresis effect, suggesting denitrification was the main pathway for 15N2O production in paddy soil with 15NO3− fertilizer added in a flooded situation. Conversely, 15NH4+ may need to be converted into 15NO3– through nitrification, then denitrified and finally released as 15N2O. Furthermore, N2O production was likely enhanced by nitrification–denitrification processes due to the water level alternating near the ground surface for AWD treatment. Consequently, the total N2O emission over the rice growing period was the highest from the AWD soils, at 2.4 times that for CIM treatments. The high proportion of N2O-N derived from soil endogenous N sources (81 % of total N2O emission) in the AWD treatment indicates that the alternating wetting–drying of soil stimulated N2O production using endogenous N mineralized from soil organic matter. Furthermore, water management of paddy soil affected N uptake by rice plants. The total N uptake by rice plants was significantly higher for CIM than for AWD and DCM treatments.

Yield reduction of direct-seeded rice under returned straw can be mitigated by appropriate water management improving soil phosphorus availability

The yield of direct-seeded rice has been shown to decrease after straw amendment. However, the reasons for the yield decrease, and any measures to alleviate it, are currently unknown. We hypothesised that straw return exerts negative effects on soil fertility and on root growth of direct-seeded rice, which subsequently reduces the remobilisation of reserves to grains under continuous flooding (CF); and that alternate wetting and drying (AWD) irrigation can alleviate these negative impacts. Field and greenhouse experiments were conducted to test the hypotheses, by comparing CF and AWD in combination with two wheat-straw treatments (incorporation and mulching). Under CF, wheat-straw incorporation decreased soil available phosphorus by 23–79%, root biomass by 10%, leaf biomass by 13%, and leaf area by 15% compared with the control with no straw incorporation; negative effects on these characteristics were lessened if the straw was mulched. The AWD treatment alleviated the negative effects of straw incorporation compared with CF, and straw mulching with AWD had no negative effects or resulted in positive effects. The results suggest that CF along with straw incorporation limits soil phosphorus availability, root growth and grain yield by affecting photosynthate accumulation and remobilisation. AWD irrigation mitigates these undesirable effects by decreasing soil total reductants, which subsequently increases soil pH and plant-available phosphorus. The proposed AWD treatment could be a promising strategy for the sustainable production of direct-seeded rice.

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.