Moderate wetting and drying increases rice yield and reduces water use, grain arsenic level, and methane emission

Enhancing root physiology for increased yield in water-saving and drought-resistance rice with optimal irrigation and nitrogen

Objectives

Water-saving and drought-resistance rice (WDR) plays a vital role in the sustainable development of agriculture. Nevertheless, the impacts and processes of water and nitrogen on grain yield in WDR remain unclear.

Methods

In this study, Hanyou 73 (WDR) and Hyou 518 (rice) were used as materials. Three kinds of nitrogen fertilizer application rate (NFAR) were set in the pot experiment, including no NFAR (nitrogen as urea applied at 0 g/pot), medium NFAR (nitrogen as urea applied at 15.6 g/pot), and high NFAR (nitrogen as urea applied at 31.2 g/pot). Two irrigation regimes, continuous flooding cultivation and water stress, were set under each NFAR. The relationships between root and shoot morphophysiology and grain yield in WDR were explored.

Results

The results demonstrated the following: 1) under the same irrigation regime, the grain yield of two varieties increased with the increase of NFAR. Under the same NFAR, the reduction of irrigation amount significantly reduced the grain yield in Hyou 518 (7.1%-15.1%) but had no substantial influence on the grain yield in Hanyou 73. 2) Under the same irrigation regime, increasing the NFAR could improve the root morphophysiology (root dry weight, root oxidation activity, root bleeding rate, root total absorbing surface area, root active absorbing surface area, and zeatin + zeatin riboside contents in roots) and aboveground physiological indexes (leaf photosynthetic rate, non-structural carbohydrate accumulation in stems, and nitrate reductase activity in leaves) in two varieties. Under the same NFAR, increasing the irrigation amount could significantly increase the above indexes in Hyou 518 (except root dry weight) but has little effect on Hanyou 73. 3) Analysis of correlations revealed that the grain yield of Hyou 518 and Hanyou 73 was basically positively correlated with aboveground physiology and root morphophysiology, respectively.

Conclusion

The grain yield could be maintained by water stress under medium NFAR in WDR. The improvement of root morphophysiology is a major factor for high yield under the irrigation regime and NFAR treatments in WDR.

Mitigation of greenhouse gas emissions and improved yield by plastic mulching in rice production

Soil mulching technologies are effective practices which alleviate non-point source pollution and carbon emissions, while ensuring grain production security and increasing water productivity. However, the lack of comprehensive understanding of the impacts of mulching technologies on rice fields has hindered progress in global implementation due to the varying environments and application conditions under which they are implemented. This study conducted a meta-analysis based on 2412 groups of field experiment data from 313 studies to evaluate the effects of soil mulching methods on rice production, greenhouse gas (GHG) emissions and water use efficiency. The results show that plastic mulching, straw mulching and no mulching (PM, SM and NM) have reduced CH₄ emissions (68.8 %, 61.4 % and 57.2 %), increased N₂O emissions (84.8 %, 89.1 % and 96.6 %), reduced global warming potentials (50.7 %, 47.5 % and 46.8 %) and improved water use efficiency (50.2 %, 40.9 % and 34.0 %) compared with continuous flooding irrigation. However, PM increased rice yield (1.6 %), while SM and NM decreased yield (4.3 % and 9.2 %). Furthermore, analysis using random forest models revealed that rice yield, GHG emissions and WUE response to soil mulching were related to climate, soil properties, fertilizer and rice varieties. Our findings can guide the implementation of plastic mulching technology in priority areas, contribute to agricultural carbon neutrality and support the development of practical guidelines for farmers.

Nitrogen fertilizer application rates and ratios promote the biochemical and physiological attributes of winter wheat

Improper optimization of the rates and ratios of nitrogen application reduces grain yields and increases the nitrogen loss, thereby affecting environmental quality. In addition, scarcer evidence exists on the integrative approach of nitrogen, which could have effects on the biochemical and physiological characteristics of wheat. Treatments were arranged as nitrogen (N) rates of 00, 75, 150, 225, and 300 kg ha^-1 in the main plots, and different nitrogen ratios were organized in subplots at 5:5:0:0 and 6:4:0:0, which were applied at the sowing, jointing, flowering, and grain filling stages. The results revealed that 225 kg N ha^-1 significantly enhanced the stomatal conductance (G _s), photosynthetic rate (P _n), intercellular CO₂ (C _i), transpiration rate (T _r), and total chlorophyll by 28.5%, 42.3%, 10.0%, 15.2%, and 50%, receptively, at the jointing stage in comparison to the control (0 kg N ha^-1). Nitrogen application of 225 kg ha^-1 increased the soil-plant analysis development (SPAD) value and the chlorophyll a, chlorophyll b, and carotenoid contents of winter wheat under the 6:4:0:0 ratio. The trend of the photosynthetic characteristics was observed to be greater at the 6:4:0:0 fertilization ratio compared to that at 5:5:0:0. The photosynthetic rate was significantly associated with the biochemical and physiological characteristics of winter wheat. In conclusion, the nitrogen dose of 225 kg ha^-1 and the ratio of 6:4:0:0 (quantity applied at the sowing, jointing, flowering, and grain filling stages) effectively promoted the photosynthetic and other physiological characteristics of winter wheat.

The Relationships among "STAY-GREEN" Trait, Post-Anthesis Assimilate Remobilization, and Grain Yield in Rice (Oryza sativa L.)

The mobilization and translocation of carbohydrates and mineral nutrients from vegetative plant parts to grains are pivotal for grain filling, often involving a whole plant senescence process. Loss of greenness is a hallmark of leaf senescence. However, the relationship between crop yield and senescence has been controversial for many years. Here, in this study, the overexpression and RNA interference lines of gene of OsNYC3 (Non-Yellow Coloring 3), a chlorophyll catabolism gene, were investigated. Furthermore, exogenous phytohormones were applied, and a treatment of alternate wetting and moderate drying (AWMD) was introduced to regulate the processes of leaf senescence. The results indicated that the delayed senescence of the "STAY-GREEN" trait of rice is undesirable for the process of grain filling, and it would cause a lower ratio of grain filling and lower grain weight of inferior grains, because of unused assimilates in the stems and leaves. Through the overexpression of OsNYC3, application of exogenous chemicals of abscisic acid (ABA), and water management of AWMD, leaf photosynthesis was less influenced, a high ratio of carbohydrate assimilates was partitioned to grains other than leaves and stems as labeled by ¹³C, grain filling was improved, especially for inferior spikelets, and activities of starch-synthesizing enzymes were enhanced. However, application of ethephon not only accelerated leaf senescence, but also caused seed abortion and grain weight reduction. Thus, plant senescence needs to be finely adjusted in order to make a contribution to crop productivity.

Arsenic in the water and agricultural crop production system: Bangladesh perspectives

The presence of high levels of carcinogenic metalloid arsenic (As) in the groundwater system of Bangladesh has been considered as one of the major environmental disasters in this region. Many parts of Bangladesh have extensively reported the presence of high levels of arsenic in the groundwater due to both geological and anthropogenic activities. In this paper, we reviewed the available literature and scientific information regarding arsenic pollution in Bangladesh, including arsenic chemistry and occurrences. Along with using As-rich groundwater as a drinking-water source, the agricultural activities and especially irrigation have greatly depended on the groundwater resources in this region due to high water demands for ensuring food security. A number of investigations in Bangladesh have shown that high arsenic content in both soil and groundwater may result in high levels of arsenic accumulation in different plants, including cereals and vegetables. This review provides information regarding arsenic accumulation in major rice varieties, soil-groundwater-rice arsenic interaction, and past arsenic policies and plans, as well as previously implemented arsenic mitigation options for both drinking and irrigation water systems in Bangladesh. In conclusion, this review highlights the importance and necessity for more in-depth studies as well as more effective arsenic mitigation action plans to reduce arsenic incorporation in the food chain of Bangladesh.

An Analysis Based on Japonica Rice Root Characteristics and Crop Growth Under the Interaction of Irrigation and Nitrogen Methods

Water shortages and nitrogen (N) fertilizer overuse limit japonica rice production in Northeastern China. The interactions between water-saving irrigation and nitrogen management on rice root and shoot growth is still our research focus. Here, japonica rice (DN425) was subjected to the irrigation methods W1 (flooding irrigation), W2 [mild alternate wetting and drying irrigation (AWD); -10 kPa], W3 (severe AWD; -30 kPa), and different N fertilizer ratios were applied in different growth stages, namely, N1 (6:3:1:0), N2 (5:3:1:1), and N3 (4:3:2:1). From jointing to full heading stages, the highest photosynthate production capacity and root activity were obtained under W1N2. AWD markedly affected the root system and resulted in root senescence at later growth stages. Grain yield and N utilization efficiency were closely and positively correlated with the relative water content, crop growth rate (CGR), leaf area duration (LAD), the increase rate of root length density, root surface area density, and root volume density (RVD) from the jointing to full heading stages. This positive correlation was also observed in the increased rate of root bleeding sap (RBS) under W1N2 and CGR under W2N3. From full heading to maturity stages, N2 could promote root growth, LAD, and CGR under AWD to a greater extent than those under the other treatments. Water use efficiency (WUE) and N uptake efficiency (NUpE) were both negatively associated with the decreased rate of RVD, root dry weight (RDW), and RBS. They were closely and positively correlated with the increased rate of RDW and CGR. Our results suggested that W2N2 treatment delayed root senescence, maintained leaf photosynthesis, optimized the crop growth rate from full heading to maturity stages, and improved grain yield. The optimal grain yield, WUE, and NUpE were achieved at the irrigation water amount and topdressing fertilizer ratio of 41.40-50.34 × 10² and 31.20-34.83 kg ha^-1, respectively.

Global benefits of non-continuous flooding to reduce greenhouse gases and irrigation water use without rice yield penalty

Non-continuous flooding is an effective practice for reducing greenhouse gas (GHG) emissions and irrigation water use (IRR) in rice fields. However, advancing global implementation is hampered by the lack of comprehensive understanding of GHGs and IRR reduction benefits without compromising rice yield. Here, we present the largest observational data set for such effects as of yet. By using Random Forest regression models based on 636 field trials at 105 globally georeferenced sites, we identified the key drivers of effects of non-continuous flooding practices and mapped maximum GHGs or IRR reduction benefits under optimal non-continuous flooding strategies. The results show that variation in effects of non-continuous flooding practices are primarily explained by the UnFlooded days Ratio (UFR, that is the ratio of the number of days without standing water in the field to total days of the growing period). Non-continuous flooding practices could be feasible to be adopted in 76% of global rice harvested areas. This would reduce the global warming potential (GWP) of CH₄ and N₂ O combined from rice production by 47% or the total GWP by 7% and alleviate IRR by 25%, while maintaining yield levels. The identified UFR targets far exceed currently observed levels particularly in South and Southeast Asia, suggesting large opportunities for climate mitigation and water use conservation, associated with the rigorous implementation of non-continuous flooding practices in global rice cultivation.

Irrigation and phosphorous fertilization management to minimize rice grain arsenic content

This research sought to minimize inorganic arsenic levels in polished rice grain by using different irrigation and phosphorous fertilization practices while also maintaining crop yield and water productivity. Two experiments were conducted during seasons 2018-2019 and 2019-2020 using a split-plot design with three blocks, five irrigation treatments (main-plots) and two phosphorous levels (sub-plots). Irrigation treatments consisted of a traditional continuous flood (CF) control and four alternatives irrigation techniques with one or two drying events during the irrigation cycle. The phosphorous fertilization levels investigated were an unfertilized control (0 kg P₂O₅ ha^-1) and the recommended fertilization level of 50 kg P₂O₅ ha^-1. Soil pH and redox potentials were measured in each treatment. Strategically-timed, low severity drying events were effective at achieving aerobic soil conditions, resulting in Eh values over 50 mV. The alternative irrigation treatment with two drying events, implemented at panicle initiation and full flowering, was the most effective in reducing inorganic arsenic in grain without affecting grain yield or the amount of irrigation water applied. This irrigation technique could be considered as an alternative management to the traditional continuous flooded to reach minimal inorganic arsenic accumulation in grain in order to attend special quality standards or specific market requirements. Accumulated inorganic arsenic in grain was below international maximum levels in all analyzed samples, with an average value of 0.084 mg kg^-1.

Saving environment through improving nutrient use efficiency under intensive use of agrochemicals in paddy fields

Increased environmental and economic costs of chemical fertilizers necessitates serious attention to improve nutrient use efficiency. A 3-year field investigation was conducted to assess the influence of different drainage systems on nitrogen (N), phosphorus (P) and potassium (K) use efficiency of two rice cultivars under alternate wetting and drying (AWD) strategy. The drying of the field was done through a surface drainage system (Control) and four subsurface drainage systems (D0.90L30, D0.65L30, D0.65L15; where D and L represent the drain depth and spacing, respectively, and Bilevel; in which the drains were spaced 15 m apart at depths 0.65 and 0.90 m). During growing seasons, the dry weight (DW) and N, P and K uptake of stem, leaf and panicle was monitored. At harvest, grain yield was also determined. Soil drying through subsurface drainage systems increased the DW of the panicle compared to surface drainage. On average, panicle DW in D0.90L30, Bilevel, D0.65L30, D0.65L15 and Control were 10.7%, 10%, 11.4%, 9.2% and 8.9% of the total DW, respectively. Improving soil aeration in the subsurface drainage systems increased crop production by increasing the share of nutrients in the panicle. The average share of N, P and K in panicle to N, P and K content of the total biomass in the subsurface-drained area was 11.7%, 12.9% and 8.4%, respectively, and in the Control was 9.7%, 10.9% and 7.9%, respectively. On average, the subsurface drainage systems improved rice grain yield and N, P and K use efficiency by 14.2% and 16%, 15% and 16% compared with Control, respectively. According to the results, subsurface drainage may effective for better aeration and increase in nutrient use efficiency in rice production systems.

Farmers’ Participatory Alternate Wetting and Drying Irrigation Method Reduces Greenhouse Gas Emission and Improves Water Productivity and Paddy Yield in Bangladesh

In dry season paddy farming, the alternate wetting and drying (AWD) irrigation has the potential to improve water productivity and paddy production and decrease greenhouse gas (GHG), such as methane (CH4) and nitrous oxide (N2O), emissions when compared to continuous flooding (CF). Participatory on-farm trials were conducted from November 2017 to April 2018 in the Feni and Chattogram districts of Bangladesh. Total 62 farmers at Feni and 43 at Chattogram district, each location has 10 hectares of land involved in this study. We compared irrigation water and cost reductions, paddy yield, and CH4 and N2O emissions from paddy fields irrigated under AWD and CF irrigation methods. The mean results of randomly selected 30 farmers from each location showed that relative to the CF irrigation method, the AWD method reduced seasonal CH4 emissions by 47% per hectare and CH4 emission factor by 88% per hectare per day. Moreover, the AWD decreased the overall global warming potential and the intensity of GHG by 41%. At the same time, no noticeable difference in N2O emission between the two methods was observed. On the other hand, AWD method increased paddy productivity by 3% while reducing irrigation water consumption by 27% and associated costs by 24%. Ultimately it improved water productivity by 32% over the CF method.

Effect of water management on microbial diversity and composition in an Italian rice field system

Traditional rice cultivation consumes up to 2500 L of water per kg yield and new strategies such as the ‘Alternate Wetting and Drying’ (AWD) might be promising water-saving alternatives. However, they might have large impacts on the soil microbiology. In this study, we compared the bacterial and archaeal communities in experimental field plots, cultivated under continuously flooding (CF) and AWD management, by high-throughput sequencing of the 16S rRNA gene. We analysed alpha and beta diversity in bulk soil and on plant roots, in plots cultivated with two different rice cultivars. The strongest difference was found between soil and root communities. Beside others, the anaerobic methanotroph Methanoperedens was abundant in soil, however, we detected a considerable number of ANME-2a-2b on plant roots. Furthermore, root communities were significantly affected by the water management: Differential abundance analysis revealed the enrichment of aerobic and potentially plant-growth-promoting bacteria under AWD treatment, such as Sphingomonadaceae and Rhizobiaceae (both Alphaproteobacteria), and Bacteroidetes families. Microorganisms with an overall anaerobic lifestyle, such as various Delta- and Epsilonproteobacteria, and Firmicutes were depleted. Our study indicates that the bulk soil communities seem overall well adapted and more resistant to changes in the water treatment, whereas the root microbiota seems more vulnerable.

Regional variability of arsenic content in Uruguayan polished rice

Characterization of the country internal variability of arsenic (As) accumulation in rice grain across different rice production regions is very important in order to analyze its compliance with international and regional limits. A robust sampling study scheme (n = 150 samples) was performed to determine total arsenic (tAs) and inorganic (iAs) levels from polished rice grain covering all rice producing regions along two growing seasons. The mean and median concentration of tAs were 0.178 mg kg-1 and 0.147 mg kg-¹, with a minimum and maximum value of 0.015 mg kg^-1 and 0.629 mg kg^-1, respectively and a coefficient of variation of 63.6%. The mean and median concentration of iAs were 0.062 mg kg^-1 and 0.055 mg kg^-1 respectively ranging from 0.005 mg kg^-1 up to a maximum of 0.195 mg kg^-1 and a coefficient of variation of 51.5%. A moderate correlation was revealed within iAs and tAs. Levels of iAs in all of the samples were below the international limits of 0.2 mg kg^-1 according to the international limits for human health by the Codex Alimentarius (FAO and WHO, 2019). Rice fields cultivated on soils originated from igneous geological material reported lower arsenic levels accumulated in rice grain in relation to sedimentary soils. Japonica cultivars presented significantly lower tAs and iAs concentrations than Indica ones (p = 0.0121 and p < 0.0001; respectively). Consumption of rice by male and female adults in Uruguay is safe according to its level of annual consumption and based on the mean iAs levels determined in this study.

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.

Effects of optimized water management on the uptake and translocation of cadmium and arsenic in Oryza sativa L. in two contaminated soils

Water management has opposite effects on the bioavailability of Cd and As in soil. In order to identify the most efficient water management strategy for reducing Cd and As accumulations and amino acid (AA) synthesis in rice in two soils with different Cd and As contents, a pot experiments were conducted in greenhouse. A treatment consisting of 5 days of flooding followed by 3 days of drainage (F5D3, repeated every 8 days) was identified as the most effective treatment for simultaneously decreasing Cd and As in grains, with reductions of grain Cd and As contents of more than 80.0% and 73.1%, respectively, compared with either a drained treatment or a flooded treatment alone; this is probably related to the high efficiency of the F5D3 treatment in reducing dissolved Cd and As according to its minimum "trade-off value" (an index for evaluating the degree of trade-off between soil solution As and Cd concentrations in water management condition), due to the variations in grain Cd and As contents which were significantly correlated with the variations in soil solution Cd (R2=0.98) and As (R2=0.92, P=0.0001) concentrations. Additionally, grain Cd content was also significantly related to the organs Cd contents (especially root Cd content, R2=0.99) and the root-to-shoot Cd translocation factors (R2=0.99), whereas grain As content was significantly related to soil Eh (R2=-0.82, P=0.003) and pH (R2=0.88, P=0.0008). The AA contents in organs under the F5D3 treatment were lower than those under the flooded and drained treatments. These results indicated that the F5D3 treatment was the most effective water management strategy for simultaneously reducing grain Cd and As contents and AA synthesis in rice, which was probably due to there being no need for rice to synthesize abundant AAs to chelate metal ions.

Arsenic speciation in rice bran: Agronomic practices, postharvest fermentation, and human health risk assessment across the lifespan

Arsenic (As) exposure is a global public health concern affecting millions worldwide and stems from drinking water and foods containing As. Here, we assessed how agronomic practices and postharvest fermentation techniques influence As concentrations in rice bran, and calculated health risks from consumption. A global suite of 53 rice brans were tested for total As and speciation. Targeted quantification of inorganic As (iAs) concentrations in rice bran were used to calculate Target Hazard Quotient (THQ) and Lifetime Cancer Risk (LCR) across the lifespan. Mean iAs was highest in Thailand rice bran samples (0.619 mg kg^-1) and lowest in Guatemala (0.017 mg kg^-1) rice bran samples. When comparing monosodium-methanearsonate (MSMA) treated and the Native-soil counterpart under the irrigation technique Alternate Wetting and Drying (AWD) management, the MSMA treatment had significantly higher total As (p = 0.022), and iAs (p = 0.016). No significant differences in As concentrations were found between conventional and organic production, nor between fermented and non-fermented rice bran. Health risk assessment calculations for the highest iAs-rice bran dosage scenario for adults, children and infants exceeded THQ and LCR thresholds, and LCR was above threshold for median iAs-rice bran. This environmental exposure investigation into rice bran provides novel information with food safety guidance for an emerging global ingredient.

Effects of silkworm excrement and water management on the accumulation of Cd and As in different varieties of rice and an assessment of their health risk

Rice (Oryza sativa L.) consumption represents a major route for the exposure to cadmium (Cd) and arsenic (As) in many countries. Two varieties of rice that were grown in soils contaminated with Cd and As were evaluated for the accumulation of these toxins in rice grains and the risks of exposure of local residents to Cd and As when treated with different amounts of silkworm excrement and types of water management. Silkworm excrement, water management and the variety of rice significantly affected the accumulation of Cd and As in rice. The combination of multiple measures can be more effective at reducing heavy metals than the use of single measure, i.e., silkworm excrement management, water management, and the selection of low accumulation variety. The use of a variety that accumulates low amounts of Cd combined with 1% silkworm excrement management can effectively increase the soil pH and electrical conductivity (EC) and decrease the contents of soil available Cd and the transfer coefficients of Cd in rice, subsequently reducing the concentrations of Cd in rice grains and lowering the health risks of the intake of Cd. Similarly, the use of a conventional rice variety combined with alternating periods of drying and wetting in the three weeks before and after the heading stage decreased the contents of soil available As and the transfer coefficient of As in rice, subsequently reducing the accumulation of As in the grains and lowering the health risk of the intake of As. The significantly lower concentrations of Cd and As in rice grains and the risk of intake of Cd and As from rice was observed using a conventional rice variety combined with alternating drying-wetting in the three weeks before and after the heading stage and 1% silkworm excrement management. Thus, the combination of multiple measures in the coexistence of Cd and As in contaminated soils can be a promising strategy to avoid serious health risks and ensure the safety of food for local residents.

Abscisic acid priming regulates arsenite toxicity in two contrasting rice (Oryza sativa L.) genotypes through differential functioning of sub1A quantitative trait loci

Arsenite [As(III)] toxicity causes impeded growth, inadequate productivity of plants and toxicity through the food chain. Using various chemical residues for priming is one of the approaches in conferring arsenic tolerance in crops. We investigated the mechanism of abscisic acid (ABA)-induced As(III) tolerance in rice genotypes (cv. Swarna and Swarna Sub1) pretreated with 10 μM of ABA for 24 h and transferred into 0, 25 and 50 μM arsenic for 10 days. Plants showed a dose-dependent bioaccumulation of As(III), oxidative stress indicators like superoxide, hydrogen peroxide, thiobarbituric acid reactive substances and the activity of lipoxygenase. As(III) had disrupted cellular redox that reflecting growth indices like net assimilation rate, relative growth rate, specific leaf weight, leaf mass ratio, relative water content, proline, delta-1-pyrroline-5-carboxylate synthetase and electrolyte leakage. ABA priming was more protective in cv. Swarna Sub1 than Swarna for retrieval of total glutathione pool, non-protein thiols, cysteine, phytochelatin and glutathione reductase. Phosphate metabolisms were significantly curtailed irrespective of genotypes where ABA had moderated phosphate uptake and its metabolizing enzymes like acid phosphatase, alkaline phosphatase and H⁺/ATPase. Rice seedlings had regulated antioxidative potential with the varied polymorphic expression of those enzymes markedly with antioxidative enzymes. The results have given the possible cellular and physiological traits those may interact with ABA priming in the establishment of plant tolerance with As(III) over accumulation and, thereby, its amelioration for oxidative damages. Finally, cv. Swarna Sub1 was identified as a rice genotype as a candidate for breeding program for sustainability against As(III) stress with cellular and physiological traits serving better for selection pressure.

Sprinkler irrigation in the production of safe rice by soils heavily polluted by arsenic and cadmium

Among the factors affecting the bioaccumulation of As and Cd in rice, a key role is played by the irrigation methods. The sprinkler irrigation (SP), optimized for rice in Sardinia, Italy, applied to several rice genotypes over many years has produced no differences in yields in comparison to what observed using the traditional continuous flooding irrigation method (CF). Because all the previous SP trials have been performed just on one, unpolluted soil, the principal aim of this study is to ascertain the effectiveness of SP to simultaneously minimize the bioaccumulation of As and Cd in rice grain even in soils severely polluted by As and/or Cd. Hence, a Carnise rice genotype was cultivated in an open field in: i) an unpolluted soil; ii) a soil polluted with 55 mg kg^-1 of As; iii) a soil polluted with 40 mg kg^-1 of Cd; iv) a soil polluted with 50 mg kg^-1 of As and 50 mg kg^-1 of Cd. In the worst condition of pollution, the amounts of total As and Cd measured in the kernels using a fully validated ICP-MS method is 90 ± 10 μg kg^-1 and 50 ± 20 μg kg^-1, respectively, i.e. less than 50% and the 25% of the maximum concentration set for these elements in rice by the European Community (200 μg kg^-1 for the inorganic As and the total amount of Cd, respectively). SP might represent a simple and valuable tool able to produce safe rice also from soils where the traditional irrigation might produce inedible rice only.

The environmental fate of phenanthrene in paddy field system and microbial responses in rhizosphere interface: Effect of water-saving patterns

The effects of water-saving patterns (Semi-dry water-saving, B; Shallow-wet control irrigation, Q; Traditional flooding irrigation, C; and Moistening irrigation, S) on the environmental fate of phenanthrene (Phe) and microbial responses in rhizosphere were investigated in paddy field system. Results showed the rice grain in Q treatment was more high production and safety with less Phe residue (up to 18%-49%) than other treatments, and the residual Phe in soil declined in the order: C (14.17%) > S (13.36%) > B (5.86%)>Q (2.70%), which proves the existence of optimal water conditions for PAHs degradation and rhizosphere effect during rice cultivation. Laccase (LAC) and dioxygenase (C23O) played important roles in Phe degradation, which were significantly positively correlated with Phe dissipation rate in soil (p < 0.01). Moreover, their activities in Q treatment, rhizosphere and subsoil were higher than those in C treatment, non-rhizoshere and upper layer soil. The introduction of Phe and rice into paddy field system decreased the microorganism diversity, and promoted the activities of enzymes and some PAHs degrading bacteria, such as Delftia, Serratia, Enterobacter, Pseudomonas, norank_f_Rhodospirillaceae, norank_f_Nitrosomonadaceae and so on. According to the cluster analysis, redundancy analysis and correlation analysis between bacterial community composition and environmental factors, water-saving patterns markedly impacted the relative abundance and bacterial community structure by the regulating and controlling on environmental conditions of paddy field. The dioxygenase activity, laccase activity, oxidation-reduction potential and conductivity were the main affecting factors on Phe dissipation during growth stage of rice.

Alternate wetting and drying irrigation and phosphorus rates affect grain yield and quality and heavy metal accumulation in rice

Alternate wetting and drying (AWD) irrigation was reported to increase rice root activity and element bioavailability, which results in enhanced heavy metal (HM) absorption and this HM ends up in rice grains. HM uptake was also affected by the levels of phosphorus (P) fertilizer application. HMs enter food chain via consumption of rice grains and cause health problems. In this study, we compared the differences in grain yield, grain quality, water use efficiency (WUE), partial factor productivity of applied P (PFPp), HM contents in different tissues and transfer coefficient (TC) of HMs under a combination of treatments involving two irrigation regimes (continuous flooding (CF) and AWD irrigation) and three P fertilizer application levels (0.4 g P₂O₅/kg soil, HP; 0.2 g P₂O₅/kg soil, MP; 0 g P₂O₅/kg soil, LP). Compared to CF, AWD irrigation increased grain yield (without reducing grain quality), decreased irrigation water use and the number of irrigation events needed and improved WUE and PFPp at all three P fertilizer application levels, while the accumulation of HMs in grains increased when more P was applied. This accumulation of HMs in grains thus requires immediate attention to the level of P fertilizer application and its optimization in water-saving AWD irrigation to minimize grain HM content.

Water irrigation management affects starch structure and physicochemical properties of indica rice with different grain quality

The effects of water irrigation management including conventional irrigation (CK), constant flooding irrigation (CFI) and alternate wetting and drying (AWD) on starch structure and physicochemical properties of two indica rice cultivars with good- and poor-quality were evaluated in the field condition with two years. The results showed that AWD could significantly increase peak viscosity, breakdown and gelatinization temperature, decreased setback and gelatinization enthalpy in two indica rice cultivars. However, starch granule size and amylopectin chain length distribution were differed the trends in the rice cultivars and treatments. AWD reduced starch granules size and amylopectin short chain, especially for large starch granules, but increased medium and long chain, which might contribute to better thermal stability and pasting viscosity for good-quality cultivar. Our study indicated that water irrigation management affected starch structure and physicochemical properties of indica rice starch, and would provide favorable information for improvement of rice starch in food industry.

Relationship between soil solution electrochemical changes and methane and nitrous oxide emissions in different rice irrigation management systems

Rice (Oryza sativa L.) intermittent irrigation is a potential strategy to mitigate methane (CH₄) and nitrous oxide (N₂O) emissions, but the effects of dry-wetting intervals on soil electrochemical changes and plant characteristics should be considered. This study was conducted in a greenhouse evaluating CH₄ and N₂O fluxes in rice under five different irrigation management practices (continuous irrigation (CI), intermittent irrigation with flooding resumption in saturated soil condition (SSI) and soil moisture at field capacity (FCI), saturated soil and irrigation resumption with soil moisture bellow field capacity (FCS), and soil at field capacity (FCD)) and its relation to plant development and global warming potential (GWP). Soil electrochemical conditions and CH₄ and N₂O emissions were expressively affected by irrigation management. The CI system presented the greatest CH₄ flux (20.14 g m^-2) and GWP (462.7 g m^-2 eq. CO₂), whereas intermittent irrigation expressively reduced CH₄ emissions. Overall, the N₂O flux was low (bellow 20 μg m^-2 h^-1) even with N application, with greater emissions occurring at the FCD treatment at the beginning of the rice season. Soil moisture at field capacity had no CH₄ flux but presented greater GWP (271 g m^-2 eq. CO₂) than intermittent irrigation systems due to N₂O flux while compromising rice plant development. The best soil moisture condition to initiate a flooding cycle during intermittent irrigation is at saturated soil conditions.

Alternate wetting and drying irrigation increases water and phosphorus use efficiency independent of substrate phosphorus status of vegetative rice plants

Sustainable approaches to rice cultivation that apply less irrigation and chemical fertilisers are required to increase crop resource use efficiency. Although alternate wetting and drying (AWD) has been widely promoted as a water-saving irrigation technique, its interactions with phosphorus (P) nutrition have attracted little attention. Vegetative rice plants were grown with two phosphorus levels, fertilised (HP) or un-fertilised (LP), and either continuous flooding (CF) or AWD irrigation. Treatment effects on substrate P bioavailability (measured by Diffusive Gradients in Thin films - DGT-P), plant and substrate water relations, and foliar phytohormone status, were assessed along with P partitioning in planta. Shoot biomass and leaf area under different irrigation treatments depended on substrate P status (significant P x irrigation interaction), since LP decreased these variables under CF, but had no significant effect on plants grown under AWD. AWD maintained DGT-P concentrations and increased maximal root length, but decreased root P concentrations and P offtake. Substrate drying decreased stomatal conductance (g_s) and leaf water potential (Ψ_leaf) but re-flooding increased g_s. AWD increased foliar abscisic acid (ABA), isopentenyl adenine (iP) and 1-aminocyclopropane-1-carboxylic acid (ACC) concentrations, but decreased trans-zeatin (tZ) and gibberellin A1 (GA1) concentrations. Low P increased ACC and jasmonic acid (JA) concentrations but decreased gibberellin A4 (GA4) concentrations. Across all treatments, stomatal conductance was negatively correlated with foliar ABA concentration but positively correlated with GA1 concentration. Changes in shoot phytohormone concentrations were associated with increased water and phosphorus use efficiency (WUE and PUE) of vegetative rice plants grown under AWD.

Simulating Soybean–Rice Rotation and Irrigation Strategies in Arkansas, USA Using APEX

With population growth and resource depletion, maximizing the efficiency of soybean (Glycine max [L.] Merr.) and rice (Oryza sativa L.) cropping systems is urgently needed. The goal of this study was to shed light on precise irrigation amounts and optimal agronomic practices via simulating rice–rice and soybean–rice crop rotations in the Agricultural Policy/Environmental eXtender (APEX) model. The APEX model was calibrated using observations from five fields under soybean–rice rotation in Arkansas from 2017 to 2019 and remote sensing leaf area index (LAI) values to assess modeled vegetation growth. Different irrigation practices were assessed, including conventional flooding (CVF), known as cascade, multiple inlet rice irrigation with polypipe (MIRI), and furrow irrigation (FIR). The amount of water used differed between fields, following each field’s measured or estimated input. Moreover, fields were managed with either continuous flooding (CF) or alternate wetting and drying (AWD) irrigation. Two 20-year scenarios were simulated to test yield changes: (1) between rice–rice and soybean–rice rotation and (2) under reduced irrigation amounts. After calibration with crop yield and LAI, the modeled LAI correlated to the observations with R2 values greater than 0.66, and the percent bias (PBIAS) values were within 32%. The PBIAS and percent difference for modeled versus observed yield were within 2.5% for rice and 15% for soybean. Contrary to expectation, the rice–rice and soybean–rice rotation yields were not statistically significant. The results of the reduced irrigation scenario differed by field, but reducing irrigation beyond 20% from the original amount input by the farmers significantly reduced yields in all fields, except for one field that was over-irrigated.

Efficiency and risks of selenite combined with different water conditions in reducing uptake of arsenic and cadmium in paddy rice

The co-contamination of arsenic (As) and cadmium (Cd) in soils is a common problem. Selenium (Se) can reduce the uptake of As and Cd in plants, and in practice, the alternate wetting and drying is a common culture mode in rice production. However, it is unknown whether Se can efficiently reduce As and Cd concentrations in crops suffering from a high-level contamination of As and Cd under different soil water conditions. In this study, we assessed the efficiency and risks of selenite [Se(IV)], in a pot experiment, to reduce the uptake of As and Cd in a rice plant (YangDao No 6) growing in a heavily contaminated soil by As and Cd (pH 7.28) under different soil water conditions. The results showed that Se(IV) failed to control the grain total As and Cd concentrations within their individual limited standard (0.2 mg kg^-1) despite that Se(IV) significantly reduced the grain total As and Cd concentrations. The soil drying treatment alone could reduce the accumulation of arsenite [As(III)] in the grains, but additional Se(IV) stimulated the accumulation of As(III) in the grains under soil drying conditions. In addition, the addition of Se(IV) enhanced the As and Cd concentrations in the shoots and/or roots of rice plants under certain conditions. The above results all suggested that the utilization of Se(IV) in a high contaminated soil by As and Cd cannot well control the total concentrations of As and Cd in plants. In this study, the available concentrations of As and Cd in the rhizosphere soil, the rhizosphere soil pH, the formation of root iron/manganese plaques and the concentrations of essential elements in the grains were monitored, and the related mechanisms on the changes of these parameters were also discussed. This study will give a guideline for the safe production of rice plants in a heavily co-contaminated soil by As and Cd.

Co-production of knowledge and adaptation to water scarcity in developing countries

Dwindling of freshwater resources is a harsh reality of the arid and semi-arid regions of the world and climate change is expected to deteriorate their situation through major reduction of freshwater supplies. Co-production of knowledge, through active negotiation of experts, government and local stakeholders has been used as a strategy to adapt to water scarcity. However, in many developing countries, co-production of knowledge is not common and adaptation efforts rarely reflects the plurality of involved knowledge sources and actors. Given the urgent need of transition towards water-efficient agricultural practices, the Iran's government applied the knowledge co-production approach and implemented an integrated participatory crop management (IPCM) project in the Bakian village, Fars province. The objectives of this study were to analyze the knowledge co-production process, identify the factors contributing to adoption of the co-produced knowledge and investigate the corresponding social, economic and environmental impacts. A mixed-method research was conducted comprising a case study on 19 informants selected using purposive sampling and a survey of 150 rice producers selected through systematic random sampling. The results indicated the relevance and pertinence of knowledge co-production in recognizing the real problems of the rice producers and suggesting some potential adaptive strategies. Though a wide range of natural, financial, technical, institutional and structural constraints restricted adoption of the proposed adaptive strategies, application of the co-produced knowledge significantly increased water productivity, ensured higher yields and farm-based sustainable livelihoods, and enhanced resilience of the farm households under water scarcity. Some recommendations and implications are offered to increase adaptation of farm families to water scarcity.

Moderate water stress in rice induces rhizosheath formation associated with abscisic acid and auxin responses

The rhizosheath is known to be beneficial for drought resistance in many plants, but the regulation of rhizosheath formation in rice plants is unclear. Here, we investigate rhizosheath formation in different rice varieties and root hair mutants. Our results showed that moderate water stress in rice induced rhizosheath formation. The soil porosity and water content were higher in the rice rhizosheath than in the rice bulk soil under moderate water stress. Additionally, rhizosheath formation in short root hair mutants was lower than in wild-type rice under moderate water stress. Moreover, transcriptomic results indicated that abscisic acid (ABA) and auxin were involved in root and root hair responses in rhizosheath formation. Further, blocking ABA and auxin pathways in wild type and in rhl1-1, the shortest root hair mutant, rhizosheath formation and root hair length were significantly decreased under moderate water stress. However, wild type plants maintained a higher root ABA content, root basipetal auxin transport, root hair length, and amount of rhizosheath than did rhl1-1. Our results suggest that moderate water stress in rice induces rhizosheath formation by modulating the ABA and auxin responses to regulate root and root hair growth, which may be used to breed rice varieties resistant to drought.

Simultaneous stimulation of arsenic methylation and inhibition of cadmium bioaccumulation in rice grain using zero valent iron and alternate wetting and drying water management

Studies aiming to limit bioaccumulation of arsenic (As) and cadmium (Cd) in rice grain has attracted global attention. In this study, simultaneous impact of zero valent iron (Fe⁰) and various water management regimes (continuous flooding (CF), alternate wetting and drying (AWD) and low water (LW)) on rice grain yield (GYM) and bioaccumulation of As and Cd in unpolished rice grain (URG) were investigated. Compared to respective control treatments, Fe⁰ significantly reduced GYM under LW by 32% (p < 0.001) and significantly increased GYM under AWD by 24% (p = 0.009; F = 5.9) but had no significant effect on GYM under CF water management regime (p > 0.05). The grain harvest index was significantly higher in Fe⁰ amended rice under AWD (67%; p < 0.001) and CF (35%; p = 0.001) compared to those without Fe⁰ amendment. Fe⁰ significantly reduced tAs in URG under LW by 32% (p < 0.017) and significantly increased tAs in URG under AWD by 37% (p = 0.007) but had no significant effect on tAs in URG under CF (p > 0.05). The Cd concentrations were significantly reduced by 51% (p = 0.002) and 61% (p < 0.003) in URG under LW and AWD respectively compared to the respective control treatments. The Dimethylarsinic acid (DMA) in unpolished rice (URG) under AWD (+Fe⁰) was significantly higher (p < 0.01; F = 11.3) compared to that accumulated in URG under AWD(-Fe°). Despite increasing As accumulation in AWD water management, simultaneous use of AWD water management and Fe° increased grain yield, enhanced accumulation of less toxic methylated As in rice grains and accumulated low Cd concentrations comparable to that attainable with CF water management indicating that simultaneous use AWD and Fe° can be effective in controlling Cd accumulation in paddies highly contaminated with Cd.

Effects of mild alternate wetting and drying irrigation and mid-season drainage on CH4 and N2O emissions in rice cultivation

Rice, one of the major sources of CH₄ and N₂O emissions, is also the largest consumer of water resources. Mild alternate wetting and drying (AWD) irrigation is widely adopted to save irrigation water resources and maintain rice production, but its effects on CH₄ and N₂O emissions are unclear. In addition, previous studies have revealed different effects of mid-season drainage on global warming potential (GWP), owing to the different criteria used. In this study, a pot experiment was conducted to investigate the effects of mild AWD irrigation and mid-season drainage (a specific soil moisture) on CH₄ and N₂O emissions during rice cultivation. Four water management systems were applied: AWD + D0 (mild AWD irrigation without mid-season drainage), AWD + D1 (mild AWD irrigation with mid-season drainage), CF + D0 (continuous flooding without mid-season drainage) and CF + D1 (continuous flooding with mid-season drainage); nitrogen was applied at two levels (N90 and N180) along with each treatment. The results showed that mild AWD irrigation reduced CH₄ cumulative emissions by an average of 87.1% but increased N₂O cumulative emissions by an average of 280% compared to the values observed with CF irrigation. Mid-season drainage did not affect N₂O emissions but interrupted CH₄ fluxes and significantly reduced CH₄ cumulative emissions. CH₄ and N₂O cumulative emissions were reduced by an average of 25.0% and 54.2%, respectively, with N90 application compared to values observed with N180 application. Unexpectedly, mild AWD irrigation did not reduce GWP and yield-scaled GWP unlike CF irrigation because a high N₂O emission peak occurred during mild AWD irrigation. Furthermore, we observed an obvious trade-off between CH₄ and N₂O. We suggest that maintaining flooding during nitrogen application but applying mild AWD irrigation for the remaining period may be helpful in reducing CH₄ and N₂O emissions and GWP.

Effects of water management and cultivar on carbon dynamics, plant productivity and biomass allocation in European rice systems

Water saving techniques, such as alternate wetting and drying (AWD), are becoming a necessity in modern rice farming because of climate change mitigation and growing water use scarcity. Reducing water can vastly reduce methane (CH4) emissions; however, this net climate benefit may be offset by enhanced carbon dioxide (CO2) emissions from soil. The main aims of this study were: to determine the effects of AWD on yield and ecosystem C dynamics, and to establish the underlying mechanistic basis for observed trends in net ecosystem C gain or loss in an Italian rice paddy. We investigated the effects of conventional water management (i.e. conventionally flooded paddy; CF) and AWD on biomass accumulation (aboveground, belowground, grain), key ecosystem C fluxes (net ecosystem exchange (NEE), net primary productivity (NPP), gross primary productivity (GPP), ecosystem respiration (ER), autotrophic respiration (RA), heterotrophic respiration (RH)), and soil organic matter (SOM) decay for four common commercial European rice cultivars. The most significant finding was that neither treatment nor cultivar affected NEE, GPP, ER or SOM decomposition. RA was the dominant contributor to ER for both CF and AWD treatments. Cultivar and treatment affected the total biomass of the rice plants; specifically, with greater root production in CF compared to AWD. Importantly, there was no effect of treatment on the overall yield for any cultivar. Possibly, the wetting-drying cycles may have been insufficient to allow substantial soil C metabolism or there was a lack of labile substrate in the soil. These results imply that AWD systems may not be at risk of enhancing soil C loss, making it a viable solution for climate change mitigation and water conservation. Although more studies are needed, the initial outlook for AWD in Europe is positive; with no net loss of soil C from SOM decomposition, whilst also maintaining yield.

Aeration Increases Cadmium (Cd) Retention by Enhancing Iron Plaque Formation and Regulating Pectin Synthesis in the Roots of Rice (Oryza sativa) Seedlings

BACKGROUND

Aeration and water management increasing rhizosphere oxygen amount significantly promote rice (Oryza sativa) growth and yield, but the effect of root aeration on cadmium (Cd) toxicity and accumulation in rice seedlings under hydroponic culture remains unclear.

RESULTS

Results showed that aeration promoted rice seedling growth and alleviated Cd toxicity. Transverse section discovered that Cd accelerated root mature and senescence while aeration delayed the mature and senescence of roots. Non-invasive Micro-test Technology (NMT) showed that aeration increased net O2 and Cd2+ influxes on the surface of roots while decreased net Cd2+ influx in xylem. Perls blue staining showed that aeration and Cd treatments increased iron plaque formation on the surface of roots. Results of metal concentration analysis showed that besides increasing Cd retention in iron plaque, aeration also increasing Cd retention in the cell wall of rice roots. Cell wall component analysis showed that aeration not only increased pectin content but also decreased pectin methylesterification degree (PMD) by increasing pectin methylesterase (PME) activity.

CONCLUSIONS

All of these results indicate that aeration not only delays root mature and senescence but also increases Cd retention in roots by enhancing iron plaque formation and regulating pectin synthesis in the roots of rice seedlings.

Irrigation management for arsenic mitigation in rice grain: Timing and severity of a single soil drying

The accumulation of arsenic (As) in rice grain is a public health concern since As is toxic to humans; in particular, inorganic As can cause many chronic diseases including cancer. Rice crops are prone to accumulating As, in part, due to the anaerobic soil conditions triggered by the traditional continuously flooded irrigation practice. The objective of this study was to determine how the severity and the timing (i.e. crop stage) of a single soil drying period impact total As concentration and As speciation within the rice (both white and brown) grain, compared to a continuously flooded (CF) control. Drying the soil until the perched water table reached 15 cm below the soil surface (same severity as in the "Safe Alternate Wetting and Drying"), which in this study corresponded to a soil (0-15 cm) water potential of ~0, did not decrease grain As concentrations, regardless of timing. Drying the soil to Medium Severity [MS: soil (0-15 cm) water potential of -71 kPa] or High Severity [HS: soil (0-15 cm) water potential of -154 kPa] decreased total As by 41-61%. However, inorganic As did not always decrease because the severity and the timing of soil drying affected As speciation within the grain. Overall, the soil had to be dried to HS and/or late in the growing season (i.e., at booting or heading instead of at panicle initiation) to decrease inorganic As concentration in the rice grain. This study indicates that the imposition of a single soil drying period within the growing season can mitigate As accumulation in rice grain, but it depends on the severity and timing of the drying period. Further, irrigation management affects As speciation within the rice grain and this must be considered if regulations on inorganic As are based on a percentage of total As measured.

Opportunities and Challenges for Dietary Arsenic Intervention

The diet is emerging as the dominant source of arsenic exposure for most of the U.S. population. Despite this, limited regulatory efforts have been aimed at mitigating exposure, and the role of diet in arsenic exposure and disease processes remains understudied. In this brief, we discuss the evidence linking dietary arsenic intake to human disease and discuss challenges associated with exposure characterization and efforts to quantify risks. In light of these challenges, and in recognition of the potential longer-term process of establishing regulation, we introduce a framework for shorter-term interventions that employs a field-to-plate food supply chain model to identify monitoring, intervention, and communication opportunities as part of a multisector, multiagency, science-informed, public health systems approach to mitigation of dietary arsenic exposure. Such an approach is dependent on coordination across commodity producers, the food industry, nongovernmental organizations, health professionals, researchers, and the regulatory community. https://doi.org/10.1289/EHP3997.

Interaction between contrasting rice genotypes and soil physical conditions induced by hydraulic stresses typical of alternate wetting and drying irrigation of soil

BACKGROUND AND AIMS

Alternate wetting and drying (AWD) saves water in paddy rice production but could influence soil physical conditions and root growth. This study investigated the interaction between contrasting rice genotypes, soil structure and mechanical impedance influenced by hydraulic stresses typical of AWD.

METHODS

Contrasting rice genotypes, IR64 and deeper-rooting Black Gora were grown in various soil conditions for 2 weeks. For the AWD treatments the soil was either maintained in a puddled state, equilibrated to -5 kPa (WET), or dried to -50 kPa and then rewetted at the water potential of -5 kPa (DRY-WET). There was an additional manipulated macropore structure treatment, i.e. the soil was broken into aggregates, packed into cores and equilibrated to -5 kPa (REPACKED). A flooded treatment (puddled soil remained flooded until harvest) was set as a control (FLOODED). Soil bulk density, penetration resistance and X-ray Computed Tomography (CT) derived macropore structure were measured. Total root length, root surface area, root volume, average diameter, and tip number were determined by WinRhizo.

RESULTS

AWD induced formation of macropores and slightly increased soil mechanical impedance. The total root length of the AWD and REPACKED treatments were 1.7-2.2 and 3.5-4.2 times greater than that of the FLOODED treatment. There was no significant difference between WET and DRY-WET treatments. The differences between genotypes were minimal.

CONCLUSIONS

AWD influenced soil physical properties and some root characteristics of rice seedlings, but drying soil initially to -50 kPa versus -5 kPa had no impact. Macropores formed intentionally from repacking caused a large change in root characteristics.

Increasing water productivity, nitrogen economy, and grain yield of rice by water saving irrigation and fertilizer-N management

The looming water resources worldwide necessitate the development of water-saving technologies in rice production. An open greenhouse experiment was conducted on rice during the summer season of 2016 at Huazhong Agricultural University, Wuhan, China, in order to study the influence of irrigation methods and nitrogen (N) inputs on water productivity, N economy, and grain yield of rice. Two irrigation methods, viz. conventional irrigation (CI) and "thin-shallow-moist-dry" irrigation (TSMDI), and three levels of nitrogen, viz. 0 kg N ha^-1 (N₀), 90 kg N ha^-1 (N₁), and 180 kg N ha^-1 (N₂), were examined with three replications. Study data indicated that no significant water by nitrogen interaction on grain yield, biomass, water productivity, N uptake, NUE, and fertilizer N balance was observed. Results revealed that TSMDI method showed significantly higher water productivity and irrigation water applications were reduced by 17.49% in TSMDI compared to CI. Thus, TSMDI enhanced root growth and offered significantly greater water saving along with getting more grain yield compared to CI. Nitrogen tracer (¹⁵N) technique accurately assessed the absorption and distribution of added N in the soil crop environment and divulge higher nitrogen use efficiency (NUE) influenced by TSMDI. At the same N inputs, the TSMDI was the optimal method to minimize nitrogen leaching loss by decreasing water leakage about 18.63%, which are beneficial for the ecological environment.

Genome Wide Association Mapping of Grain and Straw Biomass Traits in the Rice Bengal and Assam Aus Panel (BAAP) Grown Under Alternate Wetting and Drying and Permanently Flooded Irrigation

Growing demand for staple crops like rice will need to be achieved predominately through agricultural intensification and more efficient use of inputs. To meet this demand it is essential that the genetic diversity within rice is fully utilized. The aus subpopulation is considered an underappreciated resource within that diversity. A new rice panel, the Bengal and Assam Aus Panel (BAAP) of 266 aus accessions was generated with ∼2 million informative SNPs obtained using skim sequencing at ∼4× depth. The BAAP was grown in the field in Bangladesh in the 'boro' season under both continuously flooded and Alternate Wetting and Drying (AWD) irrigation during 2013 and 2014 in Mymensingh and during 2014 in Madhupur. Heading date, grain mass, straw biomass and harvest index were measured. The majority (94%) of BAAP accessions flowered within a relatively small window of 10 days. The AWD irrigation treatment generally caused an increase in grain mass, but no significant genotype by treatment interactions were detected for this trait. Shoot biomass was the only trait that showed evidence of genotype by treatment interaction. The average LD (Linkage Disequilibrium) decay across the genome was 243 Kbp. Genome wide association mapping revealed 115 quantitative trait loci (QTLs). There was little evidence of QTLs specific to the irrigation treatment, and only a few QTLs co-localized with known genes. However, some QTLs were detected across multiple sites and years. These QTLs should be targets for breeding, and include a region around 2.2 Mbp on chromosome 1, a large region in the middle of chromosome 7 and two regions on chromosome 11 (∼10 Mbp and ∼29 Mbp). The BAAP appears to be a valuable addition to the growing collection of GWA mapping populations of rice.