Alternate Wetting Research Articles

Arsenic accumulation in rice: Alternative irrigation regimes produce rice safe from arsenic contamination

The natural occurrence of arsenic (As) in groundwater & soils and its bioaccumulation in rice grains is a major health concern worldwide. To combat the problem, best combination of irrigation management and suitable rice variety altering As content in grains must be ensured. With this aim, a field trial was conducted with two rice varieties and water management including alternate wetting and drying (AWD) and continuous flooding (CF) irrigation regimes with As contaminated groundwater (AsW) and temporarily stored groundwater (TSG) and river water for only CF (as control). Results revealed that As content in different portions of paddy plant was significantly different (P < 0.001) with irrigation practices and rice varieties. AWD irrigation with TSG accumulated lower As in rice grains compared with CF-AsW for both varieties. Data showed that AWD-TSG practice led to 61.37% and 60.34% grain As reduction for BRRI dhan28 and BRRI dhan29, respectively, compared with CF-AsW. For Principle Component Analysis (PCA), first principle component (PC1) explained 91.7% of the variability and irrigation water As, soil total and available As, straw As, root As and husk As were the dominating parameters. With significant (P < 0.05) variation in yields between the genotypes, AWD increased grain yield by 29.25% in BRRI dhan29 Compared with CF. However, translocation factor (TF) and bioconcentration factor (BCF) for both varieties were less than one for all the treatments. The addition of this study to our knowledge base is that, AWD-TSG with BRRI dhan29 can be an As–safe practice without compromising yields.

Economics of Wet Seeded Rice as Influenced by Alternate Wetting and Drying Irrigation Regimes and Weed Management

An experiment was conducted at College Farm, Professor Jayashankar Telangana State Agricultural University, Rajendranagar, Hyderabad during rabi 2020-21 and 2021-22.The experiment was laid out in split plot design with two factors i.e., irrigation regimes (I1 : Farmers practice (continuous flooding of 2-5 cm from 3-4 days after sowing), I2: AWDI at 5 cm depletion of ponded water, I3: AWDI at 10 cm depletion of ponded water and I4: AWDI at 15 cm depletion of ponded water) and weed management practices (W1: Control (Unweeded check), W2: Pyrazosulfuron ethyl (10% WP) 20 g ha-1 PE fb Penoxsulam (1.02%) + Cyhalofop butyl (5.1%) 120 g ha-1 PoE, W3:Pyrazosulfuron ethyl (10% WP) 20 g ha-1 PE fb Penoxsulam (1.02%) + Cyhalofop butyl (5.1%) 120 g ha-1 PoE + Mechanical weeding at 45 DAS and W4: Weed free (Mechanical weeding at 15, 35 and 55 DAS with line weeding). Among the irrigation regimes, cost of cultivation and gross returns were highest in farmers practice (continuous flooding of 2-5 cm from 3-4 days after sowing) and lowest in AWDI at 15 cm depletion of ponded water. Net returns and B:C ratio was highest in AWDI at 5 cm depletion of ponded water and lowest net returns and B:C ratio was recorded in AWDI at 15 cm depletion of ponded water. Among weed management practices highest cost of cultivation, gross returns were achieved in weed free (mechanical weeding at 15, 35 and 55 DAS with line weeding) and lowest cost of cultivation and gross returns was achieved in Control (unweeded control). With respective to herbicide application highest gross returns, net returns and B:C ratio were achieved in pyrazosulfuron ethyl (10% WP) 20 g ha-1 PE fb penoxsulam (1.02%) + cyhalofop butyl (5.1%) 120 g ha-1 PoE + mechanical weeding at 45 DAS.

Alternate Wetting and Drying (AWD) on Rice Irrigation

In Malaysia, numerous methods have been subsequently established subjected to water-saving irrigation aiming to improve the common conventional irrigation system. However, among the most preferred water-saving method, alternate wetting and drying (AWD) irrigation adoption are presently in paddy cultivation yet has very limited information, especially locally. Hence, this study intended to propose two treatments, namely continuously flooded (control) and AWD irrigation, to investigate the feasibility of AWD implementation. The experiment was conducted at the paddy field of Padang Raja Kelantan, Malaysia. From the result, the agronomic performance was evaluated by several attributes under the growth performance evaluation, grain yield performance evaluation, and chlorophyll measurement. Statistical analysis was performed on the obtained data, and both growth, yield performances, and chlorophyll content resulted in no significant difference at p &lt; 0.05, a 95% confidence level.

Impact of various irrigation and establishment methods on yield and water use efficiency in rice

The field experiment was executed to evaluate the impact of various irrigation and establishment methods on yield and water use efficiency in rice during Kharif 2018. Split plot design was used in the experiment which consists of three irrigation treatments in the main plot and five rice establishment treatments in the sub plot. The results revealed that, higher yield parameters like number of panicles/m2 (364.83), number of grains per panicle (73.98), number of filled grains per panicle (60.29) were recorded with maintenance of saturation up to panicle initiation (PI) and flooding after PI. Manual transplanting among rice establishment methods recorded significantly higher test weight (25.04 g), grain yield (5253 kg/ha) and harvest index (0.45). Whereas, mechanical transplanting recorded significantly higher number of grains per panicle (74.61) straw yield (7939 kg/ha). Among different irrigation methods, alternate wetting and drying up to PI followed by flooding after PI recorded significantly lower total water usage (94.94 cm) and higher water use efficiency (52.39 kg/ha-cm). Among rice establishment methods, mechanical transplanting recorded significantly lower total water usage (117.81 cm) and higher water use efficiency (48.80 kg/ha-cm). Interaction between alternate wetting and drying up to PI followed by flooding after PI and mechanical transplanting recorded lower total water usage (81.88 cm) and also recorded higher water use efficiency (68.75 ha-cm).

Carbon Footprints and Conventional Rice Cultivation; A Case Study in Thanjavur District

Aims: The study aimed to analyse the carbon footprint of conventional rice cultivation and also the carbon economic efficiency.&#x0D; Study Design: Multi-stage random sampling was used.&#x0D; Place and Duration of Study: The study was carried out in the Thanjavur district of Tamil Nadu between April and May 2022.&#x0D; Methodology: Both primary and secondary data were used in the study. The main methodology used in finding the carbon footprint is LCA (Life Cycle Analysis). A well-structured interview schedule was used in the collection of data. Various kinds of literature were referred to find emission factors which were used in the study. A sample of 60 farmers was selected and data was collected. Also, 5 mills were visited to understand the process of milling, storage and transport of rice.&#x0D; Results: A total carbon footprint of 6720.46 Kg CO2e/ha was determined from the study for the cultivation, harvest, and post-harvest operations of rice production. Harvest and post-harvest processes result in a carbon footprint of 1851.46 Kg CO2e/ha, while the carbon footprint of cultivation is 4869 Kg CO2e/ha. In addition, the carbon economic efficiency was shown to be 23.39, meaning that the economic worth of rice production is 23.39 Rs per kg of carbon emission.&#x0D; Conclusion: An important factor in greenhouse gas emissions and a bigger carbon footprint is the use of fertilizers, irrigation techniques, and straw management. An important recommendation to reduce the carbon footprint is the alternate wetting and drying method of irrigation. A further way to lessen the environmental impact of rice farming is to use fewer fertilizers and pesticides.

Thirty years of water management research for rice in sub-Saharan Africa: Achievement and perspectives

Rice is one of the major staple foods in sub-Saharan Africa (SSA) and is mainly grown in three environments: rainfed upland and rainfed and irrigated lowlands. In all rice-growing environments, the yield gap (the difference between the potential yield in irrigated lowland or water-limited yield in rainfed lowland and upland and the actual yield obtained by farmers) is largely due to a wide range of constraints including water-related issues. This paper aims to review water management research for rice cultivation in SSA. Major water-related constraints to rice production include drought, flooding, iron toxicity, and soil salinity. A wide range of technologies has been tested by Africa Rice Center (AfricaRice) and its partners for their potential to address some of the water-related challenges across SSA. In the irrigated lowlands, the system of rice intensification and alternate wetting and drying significantly reduced water use, while the pre-conditions to maintain grain yield and quality compared to continuous flooding were identified. Salinity problems caused by the standing water layer could be addressed by flushing and leaching. In the rainfed lowlands, water control structures, Sawah rice production system, and the Smart-Valleys approach for land and water development improved water availability and grain yield compared to traditional water management practices. In the rainfed uplands, supplemental irrigation, mulching, and conservation agriculture mitigated the effects of drought on rice yield. The Participatory Learning and Action Research (PLAR) approach was developed to work with and educate communities to help them implement improved water management technologies. Most of the research assessed a few indicators such as rice yield, water use, water productivity at the field level. There has been limited research on the cost-benefit of water management technologies, enabling conditions and business models for their large-scale adoption, as well as their impact on farmers’ livelihoods, particularly on women and youth. Besides, limited research has been conducted on water management design for crop diversification, landscape-level water management, and iron toxicity mitigation, particularly in lowlands. Filling these research gaps could contribute to sustainable water resources management and sustainable intensification of rice-based systems in SSA. • Research on water management for rice cultivation in sub-Saharan Africa was reviewed. • The majority of studies aimed at improving water control in rainfed lowlands. • The studies focused mostly on improving rice yield and water productivity. • Less attention was given to cost-benefits and impact of water control technologies. • Water management was mostly studied at the field- rather than at landscape-level.

Effect of rice cultivars, organic manures, and water management on methane emissions and grain yield

AbstractTo assess the effect of different organic manures and rice cultivars on methane emissions, a pot experiment was conducted at the Yezin Agricultural University, Nay Pyi Taw, Myanmar during the wet season of 2016. Organic manures (control, compost, and cow dung) and two rice cultivars (Manawthukha and IR 50) were tested. For both rice cultivars, high grain yield was observed in the control, and the minimum grain yield was observed in the cow dung treatment. The rate and cumulative CH4 emissions in Manawthukha were higher than those in IR 50, in accordance with the yield, because of the longer growth duration. Although not significant, the lowest methane emissions were observed in the cow dung manure treatment (0.808 g CH4 kg−1 soil) against the control (0.893 g CH4 kg−1 soil) and compost (0.951 g CH4 kg−1 soil) treatments. Based on these results, a field experiment was conducted at Madaya Township, Mandalay region, Myanmar during the dry and wet seasons of 2017 to determine the effects of water management and different rates of cow dung manure on methane emission and yield of IR 50. Higher methane emissions were recorded for continuous flooding (CF) than for alternative wetting and drying (AWD). In both seasons, higher grain yields (1.8% in dry and 7.6% in wet) were recorded for AWD than for CF. Higher methane emissions were recorded from OM3 and lower emissions from OM0 in both water management practices. In AWD, methane emissions were restricted under aerated soil conditions, although a higher amount of manure was added.

Rice Growth Performance, Nutrient Use Efficiency and Changes in Soil Properties Influenced by Biochar under Alternate Wetting and Drying Irrigation

Water-saving irrigation occasionally causes an inconsequential yield loss in rice; thereby, biochar incorporation in this context has great scope due to its properties, including the release of nutrients and improving soil physicochemical properties. An experiment was conducted to investigate the effect of biochar combined with fertilizer on physiological response, water and nutrient efficiency of rice and changes in biochemical properties of soil under AWD (alternate wetting and drying) irrigation system. Two types of irrigation practice, such as AWD and CF (continuous flooding), and four types of fertilizer combination, namely T1: 25% Rice husk biochar (RHB) + 75% of recommended fertilizer dose (RFD); T2: 25% oil palm empty fruit bunch biochar (EFBB) + 75% of RFD; T3: 100% RFD; and T0: 0% biochar and fertilizer, were assigned to assess their impacts. The AWD irrigation produced a sharply reduced grain yield (210.58 g pot−1) compared to CF irrigation (218.04 g pot−1), whereas the biochar combination treatments T1 and T2 produced greater yields (260.27 and 252.12 g pot−1, respectively), which were up to 12.5% higher than RFD. Within AWD, irrigation water usage by T1 and T2 (98.50 and 102.37 g L−1, respectively) was profoundly reduced by up to 28.8%, with improved water use efficiency (WUE). The main effect of biochar treatment T1 and T2 also increased photosynthesis rate during vegetative and maturing stage (up to 17.6 and 24.4%, respectively), in addition to boosting agronomic efficiency of nitrogen (N), phosphorous (P) and potassium (K) compared to RFD (T3). Nevertheless, T1 and T2 significantly enhanced the total carbon and nitrogen; dehydrogenase and urease enzyme activities also increased in both irrigation regimes. The results reveal that the integrated application of RHB and EFBB with fertilizer in the AWD regime significantly reduces irrigation water usage and improves nutrient use efficiency, WUE and soil biochemical properties with a minimum yield penalty for rice.

Durability Studies on High Strength Concrete

High strength concrete (HSC) is very useful for recent construction technology; the major problem of HSC is the insufficient ductility. To investigate the ductility of HSC, the entire stress-strain curve, especially in the descending branch, shall be recorded. The aim of this study is to investigate the durability of High strength concrete for different replacement levels of mineral admixtures by alternate wetting and drying phenomenon which includes; acid attack, sulphate resistance and marine Environment and also to determine the compressive strength of concrete as GGBFS partial replacement for cement. Concrete mix is designed for M80 Grade of concrete using modified ACI method. Maximum Compressive Strength of 96.4MPa and 91.6 MPa at 28days were found for the HSC specimens at a partial replacement of cement with 30% of GGBFS in normal water curing and accelerated curing tank respectively. The specimens immersed in marine solution were found to have less weight loss when compared to acids and sulphate solution.

Improvement and testing of ORYZA model water balance modules for alternate wetting and drying irrigation

While the ORYZA crop model has been widely used in the simulation of rice growth, its computation ability is limited in terms of simulating the water balance components (WBCs) of paddy fields under water-saving irrigation conditions, such as alternate wetting and drying (AWD) regimes. In this study, a new water balance simulation framework (WBSF) reflecting the characteristics of AWD is integrated into the original ORYZA2000 (v2.13) model to simulate the WBC of paddy fields. In addition, algorithms for dynamically simulating the root length growing rate are added to the original ORYZA. Algorithms quantifying water stress are also modified. The improved model is further applied to paddy fields in Yongkang and Tuanlin, which are two typical rice growing areas in China. The results show that the improved model performs well at simulating WBCs. The Nash-Sutcliffe efficiency (NSE) of daily ponded water depth ranged from 0.82 to 0.94 across experiments under continuous flooding and AWD at the two sites, showing an increase in NSE of at least 0.23 compared to ORYZA (v3) levels. The absolute value of relative errors (A RE) between simulated and measured values for total irrigation and drainage amount was mostly no more than 10% and showed a reduction of at least 11%. The improved model also showed better performance in terms of evapotranspiration, percolation and root length simulation compared to ORYZA (v3). The yield predictive accuracy of the improved model is slightly better than that of ORYZA2000 (v2.13) but worse than that of ORYZA (v3), which might be due to the poor performance of nitrogen balance modules in the improved model. In general, given the results achieved, it is possible to state that the WBSF of the improved ORYZA2000 showed an enhanced capability to simulate WBCs, which are recommended for use in water balance simulations of paddy fields.

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.

Increased rice yield and reduced greenhouse gas emissions through alternate wetting and drying in a triple-cropped rice field in the Mekong Delta

For sustainable food production in the Mekong Delta, greenhouse gas (GHG) emissions from rice cropping activities need to be reduced without sacrificing rice productivity. Each year, a substantial amount of straw is incorporated into paddy soils through triple rice cropping, which is characterized by a short cropping period and nearly year-round flooding, such that a large amount of methane is emitted. Exposing these soils to oxidative conditions by altering the cropping-period water regime might have the potential to reduce GHG emissions with increased rice yield. To test this potential, a split-plot experiment was conducted in a typical triple-cropped alluvial farmer's paddy in a central delta area over five years and 15 consecutive cropping seasons.The emissions observed from the continuously inundated paddies were 1.1–2.7 times greater than the reported emission factors for Vietnamese continuously inundated paddies. A significantly higher emission peak was detected at the beginning of the rice cropping and flooding fallow periods in continuously flooded (CF) paddies than in alternate wetting and drying (AWD) paddies, although the differences in field water level and soil moisture among the paddies were negligible. AWD reduced annual methane emissions (−51 %) and increased rice yield (+9 %), presumably through enhanced translocation of carbohydrates from leaves to panicles. The amount of GHGs emitted from straw use also decreased (11 %) under AWD management because the straw production rate was significantly lowered (9 %) by enhanced nutrient translocation. These results indicate that GHG emission reduction potentials in the Mekong Delta have been underestimated by previous studies, corroborate the necessity of additional long-term observations of triple rice cropping systems and demonstrate the need for a robust methodology for monitoring the permanence of AWD effects after policies promoting its widespread dissemination take effect.

Combined Use of Biochar with 15Nitrogen Labelled Urea Increases Rice Yield, N Use Efficiency and Fertilizer N Recovery under Water-Saving Irrigation

Biochar is a potential carbon-rich soil amendment that improves the physicochemical properties of soil, besides acting as a controlled release fertilizer. An experiment was conducted to investigate the effect of biochars on rice yield, fertilizer use efficiency and recovery under water-saving irrigation by 15N isotopic tracer study. Two types of irrigation as alternate wetting and drying (AWD) and continuous flooding (CF), and four types of biochar treatments such as rice husk biochar (RHB) with 15N urea, oil palm empty fruit bunch biochar (EFBB) with 15N urea, 15N urea alone and control, were applied to assess their impact on rice. About 4% reduced grain yield with 18% improved water productivity was achieved by the AWD regime over the CF, whereas RHB and EFBB significantly increased rice yield compared to unamended soil. RHB and EFBB enhanced the water productivity up to 25.3%. The fertilizer N uptake and recovery were boosted by RHB and EFBB up to 18.8% and 24.5%, respectively. RHB and EFBB accelerated the agronomic use efficiency and partial factor productivity of N (up to 21% and 8%, respectively). RHB and EFBB profoundly enhanced the pH, the total C and N and the available N (NH4+ and NO3−) of the post-harvest soil. This study suggests that adding RHB and EFBB with urea improves fertilizer N utilization and soil N retention, and their combination with AWD could enhance rice yield with better water productivity due to their porous structure and controlled N release capacity.

Effect of potassium fertilizer and alternate wetting and drying (AWD) irrigation system for Boro rice cultivation in Faridpur region

Effect of potassium fertilizer and alternate wetting and drying (AWD) irrigation system for Boro rice cultivation in Faridpur region

Improving Nitrogen Use Efficiency in Aerobic Rice Based on Insights Into the Ecophysiology of Archaeal and Bacterial Ammonia Oxidizers.

The abundance and structural composition of nitrogen (N) transformation-related microbial communities under certain environmental conditions provide sufficient information about N cycle under different soil conditions. This study aims to explore the major challenge of low N use efficiency (NUE) and N dynamics in aerobic rice systems and reveal the agronomic-adjustive measures to increase NUE through insights into the ecophysiology of ammonia oxidizers. Water-saving practices, like alternate wetting and drying (AWD), dry direct seeded rice (DDSR), wet direct seeding, and saturated soil culture (SSC), have been evaluated in lowland rice; however, only few studies have been conducted on N dynamics in aerobic rice systems. Biological ammonia oxidation is majorly conducted by two types of microorganisms, ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB). This review focuses on how diversified are ammonia oxidizers (AOA and AOB), whose factors affect their activities and abundance under different soil conditions. It summarizes findings on pathways of N cycle, rationalize recent research on ammonia oxidizers in N-cycle, and thereby suggests adjustive agronomic measures to reduce N losses. This review also suggests that variations in soil properties significantly impact the structural composition and abundance of ammonia oxidizers. Nitrification inhibitors (NIs) especially nitrapyrin, reduce the nitrification rate and inhibit the abundance of bacterial amoA without impacting archaeal amoA. In contrast, some NIs confine the hydrolysis of synthetic N and, therefore, keep low NH4+-N concentrations that exhibit no or very slight impact on ammonia oxidizers. Variations in soil properties are more influential in the community structure and abundance of ammonia oxidizers than application of synthetic N fertilizers and NIs. Biological nitrification inhibitors (BNIs) are natural bioactive compounds released from roots of certain plant species, such as sorghum, and could be commercialized to suppress the capacity of nitrifying soil microbes. Mixed application of synthetic and organic N fertilizers enhances NUE and plant N-uptake by reducing ammonia N losses. High salt concentration promotes community abundance while limiting the diversity of AOB and vice versa for AOA, whereas AOA have lower rate for potential nitrification than AOB, and denitrification accounts for higher N2 production. Archaeal abundance, diversity, and structural composition change along an elevation gradient and mainly depend on various soil factors, such as soil saturation, availability of NH4+, and organic matter contents. Microbial abundance and structural analyses revealed that the structural composition of AOA was not highly responsive to changes in soil conditions or N amendment. Further studies are suggested to cultivate AOA and AOB in controlled-environment experiments to understand the mechanisms of AOA and AOB under different conditions. Together, this evaluation will better facilitate the projections and interpretations of ammonia oxidizer community structural composition with provision of a strong basis to establish robust testable hypotheses on the competitiveness between AOB and AOA. Moreover, after this evaluation, managing soils agronomically for potential utilization of metabolic functions of ammonia oxidizers would be easier.

Alternate wetting–drying enhances soil nitrogen availability by altering organic nitrogen partitioning in rice-microbe system

Alternate wetting and drying (AWD) irrigation influences soil nutrient cycling and the functioning of soil microorganisms. However, the effects of AWD on organic nitrogen (ON) partitioning in rice-microbe ecosystems and soil microbial communities are poorly understood. A root-box microcosm experiment with two rice varieties (Nipponbare, Nip; Yangdao 6, YD6), two irrigation regimes (conventional flood irrigation (CF); AWD) and three N application levels (zero N, N0; medium N, N1; high N, N2) was performed based on the 13C,15N-labelled glycine and 13C-phospholipid fatty acids (PLFA) techniques. Compared to CF, AWD increased soil dissolved oxygen, microbial growth and the enzymes related to N transformation, thus enhancing rice growth and the N utilization index (NUI). Approximately 4.9–10.3% and 7.7–13.6% of the exogenous glycine was directly utilized by Nip and YD6 seedlings, respectively, and its ratio increased with increasing N levels, whereas 4.4–11.2% and 4.6–10.3% were incorporated into soil microbes. It seems that rice has an appreciable capacity to utilize organic N despite fierce competition with soil microbes. The 13C:15N ratio showed that 12.5–37.5% and 11.0–41.0% of the added glycine was taken up intact by soil microorganisms in the rhizospheres of Nip and YD6. At the N1 and N2 levels, AWD increased rice 15N-glycine uptake but decreased microbial 15N-glycine uptake. Rice intact glycine uptake and soil inorganic N contents were positively correlated with rice biomass and NUI, indicating that the enhanced inorganic N under AWD is beneficial for soil ON availability and rice growth. Gram-negative and general bacteria were the dominant competitors with rice for soil ON. AWD increased the contents of gram-negative bacteria and fungi and the ratio of fungi:bacteria in rhizosphere soils. Collectively, AWD creates a good rhizosphere oxygen environment for rice and microbial growth. ON partitioning in the rice-microbe system and the adaptive adjustment of the microbial community play important roles in modulating soil nutrients for optimal rice growth.

Sustainable groundwater use in the Eastern Gangetic Plains requires region-specific solutions

This study aimed to examine whether conservation agriculture can be applied across the Eastern Gangetic Plains (EGP) as a strategy to ensure that groundwater use for irrigation remains sustainable as demands increase. The study analysed the groundwater balance in the EGP at sub-region, district and field scales using MODFLOW, a water balance model, and the APSIM model, respectively and evaluated the current state of groundwater development aiming to address sustainability concerns. Long-term groundwater use and aquifer reserves reveal the significant influence of groundwater extraction on the current state of the water balance. In the Indian and northwest Bangladesh sub-regions, accelerated extraction may result in groundwater mining in areas where potential maximum recharge has already been achieved or exceeded, while further development of groundwater may be possible in areas where actual recharge is still less than potential recharge. At district level, the water supply versus demand situation shows a large annual surplus in the East but a deficit in the West. Conservation Agriculture (CA) and Alternate Wetting and Drying (AWD) irrigation practice exert varying impacts on water demand; crop transpiration (Ep) is generally higher in CA compared to Conventional Tillage (CT), while soil evaporation (Es) is similar in both practices. Net evapotranspiration, although very similar in both practices, is generally greater in CA. AWD has a limited effect on Es but reduces the percolation rate and therefore irrigation requirement of Boro rice. In conclusion, the cause–effect associations between irrigation water use and groundwater sustainability are not spatially uniform across the EGP, nor will they likely be so under further agricultural development associated with increased water demands. The study suggests that the cause–effect interactions between irrigation water use and groundwater sustainability cannot be generalized across the EGP and, therefore, CA or AWD should not be applied uniformly across the region.

Natural 15N abundance as an indicator of nitrogen utilization efficiency in rice under alternate wetting and drying irrigation in soils with high clay contents

The 15N natural abundance is an effective indicator of nitrogen dynamics in plants. The impact of different irrigation regimes as a function of varied soil clay contents on stable nitrogen isotope abundance (δ15N) in rice remains unknown. Therefore, the response of δ15N and nitrogen utilization efficiency (NUE) of rice to different combinations of alternate wetting and drying irrigation (AWD) and clay contents were investigated. The study included three AWD regimes, viz. I100, (100 % saturation, 30 mm flooded), I90 (90 % saturation, 30 mm flooded) and I70 (70 % saturation, 30 mm flooded), and three soil clay content treatments, viz. 40 % (S40), 50 % (S50), and 60 % (S60) clay content. Compared with I100, I90 and I70 with high clay content (S60) significantly increased the crack volumes and N leaching losses and reduced the total N accumulation and different forms of NUE of rice plants. The values of δ15N in above-ground organs and soil were greatly increased by I90 and I70 irrigation regimes compared to I100. An increasing trend of organs δ15N from root to shoot was found for all three irrigation regimes. Significant negative relationships were found between (i) N partial factor productivity (PFP) and grain 15N, (ii) PFP and leaf 15N, and (iii) N harvest index (NHI) and leaf 15N. These significant negative relationships might contribute to the increased N losses and changed N allocation under AWD with high clay contents. Hence, it is suggested that cracks should be taken into consideration in rice cultivation. Moreover, δ15N may serve as an effective indicator of NUE in rice grown under AWD irrigation with high clay contents as well as an indirect indicator for assessing the N loss in agro-ecosystems.

Performance evaluation of a water level sensor under various turbidity levels in lowland crop production systems

The practice of alternate wetting and drying (AWD), a water-saving technology in lowland crop production systems, can be greatly facilitated using wireless water level sensors. However, these sensors generally work under clear water conditions. The sensitivity of these sensors to turbidity is important for accurate water level measurement and appropriate irrigation scheduling. This study evaluated the performance of a high-end water level sensor of the submersible pressure transducer type under various turbidity levels. The performance tests were performed in the laboratory using water samples collected from a typical lowland rice production system under various levels of turbidity replicated three times with clear water as control. The readings of the sensors were compared with manual readings for each turbidity level in all replications. Results showed that the measured water level depth generally increases with increasing turbidity for each voltage level. The linear regression or calibration equation developed for each turbidity level proved to be adequate as evidenced by a relatively low RMSE of less than 1 mV. Results of ANOVA suggest that turbidity significantly affects the accuracy of the water level sensor (p <.001). A unified calibration equation (R2=0.9985 and RMSE=1.971 mV) was developed to account for the effect of turbidity up to 4300 FAU on the water level measurements. Results of this study can be used to improve the accuracy of water level monitoring in irrigated lowland crop production systems employing alternate wetting and drying technology to further increase irrigation efficiencies and augment water savings particularly during the dry season or under water-scarce conditions for a more sustainable crop production.

Nutrient Dynamics of Rice Cultivars under Different Irrigation Regimes and Systems of Cultivation

ABSTRACT This study investigated the performance of rice cultivars under the best method of irrigation and system of cultivation on clay loam soils of Indian Institute of Rice Research, Rajendranagar, Hyderabad, Telangana, during the kharif seasons of 2017 and 2018. Thetreatment consisted of two irrigation regimes, viz. alternate wetting and drying (AWD) and saturation as main plot treatments; three establishment methods, viz. system of rice intensification (SRI), drum seeding (DS), and normal transplanting (NT) as subplot treatments; and four cultivars, namely DRR Dhan 42, DRR Dhan 43, MTU-1010, and NLR-34449 as sub-sub plot treatments summing up to 24 treatment combinations laid out in split–split plot design with three replications. Among the irrigation regimes, AWD noticed significantly superior nitrogen, phosphorus, and potassium uptake at 60, 90 DAS/DAT, and at harvest during 2017 and 2018 as compared to saturation. Between irrigation regimes, AWD recorded significantly superior N, P, and K use efficiency as compared to saturation. At 60, 90 DAS/DAT, and at harvest, SRI method recorded significantly superior N, P, and K uptake as compared to NT and DS during both the years. Higher NUE of nitrogen, phosphorus, and potassium was observed with SRI than DS and NT methods. N, P, and K uptake was significantly superior with DRR Dhan 43 at 60, 90 DAS, and harvest during both the years of study followed by MTU-1010. Among the rice cultivars, higher N, P, and K use efficiency was recorded in DRR Dhan 43 over other rice cultivars.