Continuous Flooding Irrigation Research Articles

Unraveling nitrogen loss in paddy soils: A study of anaerobic nitrogen transformation in response to various irrigation practice

Soil nitrogen (N) transformation processes, encompassing denitrification, anaerobic ammonium oxidation (anammox), and anaerobic ammonium oxidation coupled with iron reduction (Feammox), constitute the primary mechanisms of soil dinitrogen (N2) loss. Despite the significance of these processes, there is a notable gap in research regarding the assessment of managed fertilization and irrigation impacts on anaerobic N transformations in paddy soil, crucial for achieving sustainable soil fertility management. This study addressed the gap by investigating the contributions of soil denitrification, anammox, and Feammox to N2 loss in paddy soil across varying soil depths, employing different fertilization and irrigation practices by utilizing N stable isotope technique for comprehensive insights. The results showed that anaerobic N transformation processes decreased with increasing soil depth under alternate wetting and drying (AWD) irrigation, but increased with the increasing soil depth under conventional continuous flooding (CF) irrigation. The denitrification and anammox rates varied from 0.41 to 2.12 mg N kg−1 d−1 and 0.062–0.394 mg N kg−1 d−1, respectively, which accounted for 84.3–88.1% and 11.8–15.7% of the total soil N2 loss. Significant correlations were found among denitrification rate and anammox rate (r = 0.986, p < 0.01), Fe (Ⅲ) reduction rate and denitrification rate (r = 0.527, p < 0.05), and Fe(Ⅲ) reduction rate and anammox rate (r = 0.622, p < 0.05). Moreover, nitrogen loss was more pronounced in the surface layer of the paddy soil compared to the deep layer. The study revealed that denitrification predominantly contributed to N loss in the surface soil, while Feammox emerged as a significant N loss pathway at depths ranging from 20 to 40 cm, accounting for up to 26.1% of the N loss. It was concluded that fertilization, irrigation, and soil depth significantly influenced anaerobic N transformation processes. In addition, the CF irrigation practice is best option to reduce N loss under managed fertilization. Furthermore, the role of microbial communities and their response to varying soil depths, fertilization practices, and irrigation methods could enhance our understanding on nitrogen loss pathways should be explored in future study.

Water Stress Index and Stomatal Conductance under Different Irrigation Regimes with Thermal Sensors in Rice Fields on the Northern Coast of Peru

In the face of the climate change crisis, the increase in air temperature negatively impacts rice crop productivity due to stress from water scarcity. The objective of this study was to determine the rice crop water stress index (CWSI) and stomatal conductance (Gs) under different irrigation regimes, specifically continuous flood irrigation treatments (CF) and irrigations with alternating wetting and drying (AWD) at water levels of 5 cm, 10 cm, and 20 cm below the soil surface (AWD5, AWD10, and AWD20) in an experimental area of INIA-Vista Florida and in six commercial areas of the Lambayeque region using thermal images captured with thermal sensors. The results indicated that AWD irrigation generated more water stress, with CWSI values between 0.4 and 1.0. Despite this, the yields were similar in CF and AWD20. In the commercial areas, CWSI values between 0.38 and 0.51 were obtained, with Santa Julia having the highest values. Furthermore, a strong Pearson correlation (R) of 0.91 was established between the CWSI and Gs, representing a reference scale based on Gs values for evaluating water stress levels.

Estimación de la evapotranspiración a partir de imágenes de alta resolución de VANT para sistemas de riego en arrozales de la costa norte de Perú

In view of the growing scarcity of water for agriculture, the increase in food demand and future drought scenarios posed by climate change, it is essential to design new technologies that contribute to lower water consumption. In this research, high-resolution images have been used to estimate evapotranspiration in rice fields by applying the METRICTM (Mapping Evapotranspiration at High Resolution using Internalized Calibration) energy balance model. For this purpose, 5900 m2 of crop were monitored under continuous flood irrigation (CF) and 2600 m2 under alternate wetting and drying irrigation (AWD), in addition to some plots with lateral filtration. Ten flights were conducted between tillering and flowering phases, five flights with a Matrice 210 UAV equipped with a Parrot Sequoia multispectral camera, and five flights with a Matrice 300 RTK equipped with a H20T thermal camera. Field data were collected from vegetation indices (NDVI and LAI), and readings from a radiometer, to adjust information from multispectral and thermal images, respectively, and to obtain the components of the surface energy balance. Mean values for crop evapotranspiration (ETc) of 6.34 ± 1.49 and 5.84 ± 0.41 mm d-1 were obtained for IC irrigation and AWD irrigation, respectively, obtaining a water saving of 42% with a yield reduction of 14%, providing a guide for proper irrigation management, however, it is suggested to use the model to optimize yield by obtaining critical thresholds for optimal application of AWD in the face of water resource scarcity.

Phenology, gas exchange, biomass accumulation, and irrigated rice yield under alternative irrigation managements

AbstractIn Brazil, rice production is predominantly concentrated in the South region, employing a continuous flood irrigation system throughout the crop cycle. However, this irrigation management strategy in the tropical region contributes to low water‐use efficiency owing to adverse climatic conditions. Furthermore, with climate change projections indicating reduced water availability, the study aims to investigate the impact of alternative irrigation management strategies on the phenological development, gas exchange, biomass accumulation, and productivity of tropical irrigated rice. Three alternative irrigation management approaches—intermittent flood irrigation with aeration (IFA), intermittent flood irrigation throughout the growth cycle (IFC), and intermittent flooding up to the flowering stage (IFF)—were compared with the traditional continuous flood irrigation throughout the growth cycle. Phenological data, gas exchange, growth, and productivity dynamics were subject to analysis, providing overarching insights into management practices. Notably, irrigation management exhibited no influence on the vegetative phase of the crop. The implementation of intermittent flood irrigation facilitated a reduction in water supply without compromising the physiological performance of tropical irrigated rice. Strategies promoting judicious water utilization, such as IFA and IFC, can be readily integrated into the cultivation of tropical irrigated rice without detriment to grain yield or harvest index.

Effects of straw addition on biological nitrogen fixation under continuous and intermittent flooding irrigation in a rice cropping system

Both straw addition and water management affect biological nitrogen fixation (BNF), but it is still unclear how straw addition impacts BNF under continuous or intermittent flooding irrigation in a rice cropping system. A 15N2-labelling chamber system placed in a rice field was used to evaluate BNF under straw addition with continuous or intermittent flooding irrigation for 90 days. The nitrogenase reductase (nifH) gene and reverse transcription gene (cDNA) in the soil were amplified using Real-time polymerase chain reaction (qPCR), and nifH gene high-throughput sequencing was applied. The BNF in the straw addition treatment (14.0 g straw added to 1.40 kg soil) under continuous flooding (14.3 kg ha-1) was 116% higher than that under intermittent flooding (6.62 kg ha-1). Straw addition and continuous flooding showed significant synergistic effects on BNF and the gene copy numbers of nifH DNA and nifH cDNA. The increase in BNF was mainly due to the increase in the abundance of heterotrophic diazotrophs such as Desulfovibrio, Azonexus, and Azotobacter. These results indicate that straw addition under continuous flooding stimulates BNF relative to intermittent flooding, which may ultimately lead to a rapid enhancement of soil fertility.

Effects of integrated plant nutrition systems with fertilizer deep placement on rice yields and nitrogen use efficiency under different irrigation regimes

Improved fertilizer management, with a combination of organic and inorganic inputs, has the potential to enhance rice yield while maintaining soil health. However, studies on the effects of broadcast prilled urea (PU) and urea deep placement (UDP) applied in combination with organic inputs (poultry litter [PL] and vermicompost [VC]), as integrated plant nutrition systems (IPNSs), on rice yields and nitrogen use efficiency (NUE) under alternate wetting and drying (AWD) irrigation are limited. We conducted field experiments during the dry and wet seasons of 2018, 2019, and 2020 to investigate the effects of fertilizer treatments, including control (no nitrogen), UDP, PU, and IPNSs (PU + VC, PU + PL, and UDP + PL) on rice yield and NUE under two irrigation regimes – AWD and continuous flooding (CF). The results revealed that fertilizer treatment and irrigation regime had significant (p < 0.05) interaction effects on rice yield and the agronomic efficiency of N (AEN) during the dry season. UDP significantly (p < 0.05) boosted rice yield, total dry matter (TDM), and NUE as compared to broadcast PU in both wet and dry seasons. Similarly, the IPNS treatment of UDP with PL significantly (p < 0.05) boosted rice yield, TDM, and NUE in comparison to broadcast PU. Under AWD irrigation, UDP alone produced higher rice yields than other treatments, while UDP, and UDP with PL produced similar yields under CF irrigation. During the dry season, AWD irrigation significantly (p < 0.05) increased rice yield, TDM, and AEN when compared to CF conditions, but during the wet season, AWD irrigation demonstrated a rice yield and NUE equivalent to CF. This research implies that using a UDP alone or in combination with PL as an IPNS could be a good way to boost crop productivity while also maintaining soil fertility.

Effects of Water Management and Rice Varieties on Greenhouse Gas Emissions in Central Japan

Greenhouse gas (GHG) emissions from paddy fields depend on water management practices and rice varieties. Lysimeter experiments were conducted to determine the effect of rice varieties (lowland; Koshihikari (KH) and upland; Dourado Precoce (DP)) on GHG emissions under two water management practices: alternate wetting and drying (AWD) and continuous flooding (CF). A repeated cycle of drying and wetting in AWD irrigation was performed by drying the soil to −40 kPa soil matric potential and then rewetting. Consequently, the closed chamber method was used to measure direct emissions of methane (CH4), nitrous oxide (N2O), and carbon dioxide (CO2). The result revealed that water management significantly affected CH4 and N2O emissions (p &lt; 0.05), while no significant effect was observed between different rice varieties. Although, AWD irrigation reduced CH4 emissions, it increased N2O emissions compared to CF irrigation, likely due to increased oxygen supply. AWD irrigation decreased GWP by 55.6% and 59.6% in KH and DP, respectively, compared to CF irrigation. Furthermore, CH4 and N2O emissions significantly correlated with soil redox potential and volumetric water content. These results suggest that AWD irrigation might be an effective water management method for mitigating GHG emissions from rice fields in central Japan.

Mitigating ammonia volatilization in rice cultivation: The impact of partial organic fertilizer substitution

Optimizing water and nitrogen management to minimize NH3 volatilization from paddy fields has been extensively studied. However, there is limited research on the combined effect of different rates of organic fertilizer substitution (OFS) and irrigation methods in rice cultivation, exploring an effective water and nitrogen combination is beneficial to mitigate NH3 volatilization. To address this gap, we conducted a two-year field experiment to investigate NH3 volatilization under different OFS rates (0%, 25%, and 50%) combined with continuous flooding irrigation (CF) and alternate wet and dry irrigation (AWD). Our findings revealed that NH3 fluxes exhibited similar emission patterns after each fertilization event and significantly decreased with increasing rates of OFS during the basal stage. Compared to no substitution (ON0), the low (ON25) and high (ON50) rates of OFS reduced cumulative NH3 emissions by 18.9% and 16.6%, and lowed NH3 emission factors (EFs) by 26.7% and 23.3%, respectively. Although OFS resulted in a slight reduction in rice yield, yield-scaled NH3 emissions were significantly reduced by 11.9% and 6.5% under the low and high substitution rates, respectively. This reduction was mainly attributed to the slight yield reduction observed at the low substitution rate. Furthermore, when combined with ON0, AWD irrigation had the potential to increase NH3 volatilization. However, this increase was not observed when combined with ON25 and ON50. During each fertilization stage, floodwater + concentration emerged as the prominent environmental factor influencing NH3 volatilization, showing a stronger and more positive correlation compared to other factors such as floodwater pH, soil pH, and NH4+ concentration. Based on our findings, we recommend implementing effective water and nitrogen management strategies to minimize NH3 volatilization in rice cultivation. This involves applying a lower rate of organic fertilizer substitution during the basal stage, maintaining high water levels during fertilization, and implementing mild AWD irrigation during non-fertilization periods.

N-loaded clinoptilolite under water-saving irrigation mitigates ammonia volatilization while increasing grain yield and water-nitrogen use efficiency

Minimizing ammonia volatilization (AV) in paddy fields can not only reduce nitrogen (N) loss but also prevent environmental pollution. While clinoptilolite has been shown to effectively decrease AV, it is important to note that natural clinoptilolite contains non-desorption active sites that can hinder soil N effectiveness, ultimately leading to decreased N utilization. Therefore, we proposed modifying clinoptilolite with a weakly acidic NH4Cl solution (N-loaded clinoptilolite, NZ) to replenish exogenous N while continuously reducing AV. A lysimeter experiment was conducted under two irrigation regimes (ICF: continuous flooding irrigation; IAWD: alternate wet-dry irrigation) to examine the effect of N-loaded clinoptilolite on soil N, water-N use, AV loss and grain yield over two rice-growing seasons in Northeast China. The results show that AWD significantly reduced AV during the basal fertilization period and the first top-dressing period in 2020 and 2021. Compared with the control (without N-loaded clinoptilolite), N-loaded clinoptilolite at 10 t·ha−1 (NZ10) significantly reduced the total AV by 29% and 33% in the two years, respectively, with the most significant reduction impact (30% and 36%) occurring in the first top-dressing period. NZ10 coupled with AWD regime reduced AV more significantly and compared with conventional management (ICFNZ0), IAWDNZ10 decreased the total amount of AV by 36% and 42% in two years, respectively. N-loaded clinoptilolite also increased the soil NH4+-N and NO3--N content during the tillering and grain-filling stages of rice, which in turn increased the rate of maximum N accumulation, shortened the duration, promoted N accumulation and translocation in rice plants, and finally reduced AV. Additionally, when compared to the control, the utilization of NZ10 under the AWD irrigation regime resulted in an average 29% reduction in irrigation water usage and a yield increase of 5% over two years. Thus, IAWDNZ10 was not only highly productive and water-efficient but also significantly reduced AV, making it an environmentally friendly and effective management model for on-farm practices.

Effects of five-year field aged zeolite on grain yield and reactive gaseous N losses in alternate wetting and drying paddy system

Clinoptilolite zeolite has been widely used in agricultural production systems for enhancing water and fertilizer savings, mitigating greenhouse gas emissions, and increasing yield. However, there is little information on field-aged effects of zeolite on reactive gaseous N losses under alternate wetting and drying irrigation (AWD). We conducted a five-year field experiment to investigate field-aged effect of natural zeolite addition at 0 (Z0), 5 (Z5), and 10 (Z10) t ha−1 on reactive gaseous N losses (NH3, N2O), N-related global warming potential (GWPN), soil properties and grain yield under two irrigation regimes (CF: continuous flooding irrigation; AWD) in the 4th (2020) and 5th (2021) years since its initial application in 2017. As compared with CF, AWD did not significantly affect grain yield and NH3 volatilization but increased seasonal N2O emissions by 46 %–71 % over two years. Zeolite increased rice yield for five consecutive years. Z10 reduced averaged cumulative NH3 volatilization and GWPN by 23 % and 26 %, compared to zeolite-free treatment, respectively, in the 4th and 5th years. Soil NH4+-N was increased with the increased rate of Z application under both CF and AWD. Z10 increased soil NH4+-N by 27 %–38 % and NO3−-N by 14 %–22 % in five years, compared to Z0, respectively. Compared to AWD without zeolite, the addition of 10 t ha−1 zeolite under AWD lowered NH3 volatilization, cumulative N2O emissions, and GWPN by an average of 28 %, 29 %, and 30 % in two years, respectively. IAWDZ10 did not differ from ICFZ0 on reactive gaseous N losses but significantly lowered reactive gaseous losses relative to IAWDZ0. Therefore, zeolite addition could mitigate the reactive gaseous N losses and GWPN for at least five years after initial application, which is beneficial to promoting zeolite application and ensuring sustainable agriculture.

Effect of planting and irrigation management strategies on growth, yield and water productivity of indica rice in Iran

Abstract One of the most important problems for rice production is the high water need of this plant. Therefore, the use of modern technologies to increase water-saving in paddy fields is critical to global food security. Hence, the present study aimed to evaluate the effects of different planting methods and irrigation systems on growth, yield and water productivity in rice. The experiment was arranged as a split-plot in a randomized complete block design with three replications. The experimental treatments included the main plot assigned to three planting methods (transplanting at puddled bed [TPB], transplanting at non-puddled bed [TNPB], and direct-seeded rice [DSR]) and the sub-plot assigned to three irrigation systems (continuous flooding irrigation (CFI), alternate wetting and drying [AWD], and drip irrigation [DI]). The results showed that the highest grain yield (3962.7 kg.ha−1) and more-water-saving (17.3%) was achieved in the TPB treatment. Total water productivity for TPB, TNPB, and DSR methods were calculated to be 0.56, 0.43, and 0.34 kg.m−3, respectively. Grain yield in CFI (3457.6 kg.ha−1) and AWD (3410.3 kg.ha−1) systems was significantly higher than DI treatment (3150.7 kg.ha−1), while no significant difference was observed between CFI and AWD treatments in terms of rice production. However, the AWD system increased water-saving by 24.8% compared with CFI. Our results highlight that combined application of AWD system and TPB method has a great potential to reduce total water input without negatively affecting yield.

Biochar-mediated Cd accumulation in rice grains through altering chemical forms, subcellular distribution, and physiological characteristics

Biochar can change the availability and morphology of soil Cd. However, the influence of biochar on Cd chemical form and subcellular fraction in rice is poorly understood, particularly under different irrigation methods. A pot experiment of biochar application combined with two irrigation methods (continuous flooding and intermittent irrigation, CF and II) was conducted. The Cd accumulation, chemical form and subcellular fraction in rice organs and the associated physiological responses were examined. Biochar significantly reduced soil available Cd (30.85–47.26% and 32.35–52.35%) under CF and II but increased the Cd content (30.4–63.88% and 13.03–18.59%) in brown rice. Additionally, the Cd content in shoots/grains under II was higher than that under CF. Biochar elevated the Cd soluble fraction in roots while lowered the cell wall fraction under both irrigation methods, whereas the opposite result was observed in leaves. Biochar increased water-, ethanol-, and NaCl-extractable Cd in roots meanwhile increased ethanol-extractable Cd in leaves under both irrigation methods. Moreover, the total amount of water-, ethanol-, and NaCl-extractable Cd in rice roots was higher under II than under CF. Related hormones and antioxidant enzymes may also be involved in biochar-mediated Cd accumulation in rice grains. Thus, changes in Cd chemical form and subcellular fraction in the root and leaf are the main mechanisms of biochar-induced rice grains Cd accumulation.Graphical

Exogenous Application of Methyl Jasmonate Promotes Yield and Grain Quality of Rice under Terminal Drought Stress

Exogenous application of methyl jasmonate (MeJA) improves rice drought tolerance, but its effects on rice yield and quality under drought stress during the reproductive phase remain unclear. A pot experiment was conducted to measure rice yield, grain quality, and starch physicochemical properties under three treatments: continuous flooding irrigation throughout the whole growth season (CF), ten days of −40 kPa drought stress at the heading stage (DS), and foliar spraying 100 μmol L−1 MeJA on the first three days of the ten-day −40 kPa heading stage drought stress (DM). An inbred japonica rice variety, Huaidao 5, was the experimental material, and each treatment had 11 replicates for sampling. The results indicated that DS significantly reduced rice yield and quality compared to CF. With increases in superoxide dismutase (+22.2%), peroxidase activities (+10.5%), catalase (+5.0%), and proline content (+5.7%), DM significantly increased 1000-grain weight (+8.6%), filled grain percentage (+3.6%), and yield (+11.1%) compared with DS. Regarding grain quality, DM significantly decreased the chalkiness degree (−12.3%) and protein content (−3.9%) but increased the amylose content (+17.2%) and taste value (+7.3%) relative to DS. In addition, DM improved breakdown viscosity (+17.8%), gelatinization enthalpy (+17.2%), retrogradation enthalpy (+28.0%), 1045/1022 cm−1 ratio (+3.0%), and starch granule morphology compared to DS. In conclusion, exogenous application of 100 μmol L−1 MeJA enhanced the antioxidant capacity of rice leaves, and thus improved starch physicochemical properties to increase grain yield and quality under terminal drought stress.

A combination of organic fertilizers partially substitution with alternate wet and dry irrigation could further reduce greenhouse gases emission in rice field

Alternate wet and dry (AWD) irrigation and organic fertilizers substitution (OFS) have contrasting effects on CH4 and N2O emissions in rice cultivation. Combining these two practices may be feasible for simultaneous reduction of CH4 and N2O emission from paddy. Hence, we conducted a two-year field experiment to explore the reduction of greenhouse gases under the combination of AWD and OFS. The field experiment which was designed with two irrigation methods (continuous flooding (CF) irrigation and AWD irrigation), and five nitrogen regimes (N0, N135, and N180 represent 0, 135, and 180 kg N ha-1, respectively, ON25 and ON50 represent 25% and 50% OFS for inorganic fertilizer, respectively). The results showed a single-peak emission for CH4 fluxes during the whole rice growing season in all water and nitrogen treatments while the N2O fluxes peak only observed during tillering period with AWD irrigation. AWD irrigation and OFS showed a limited reduction in global warming potential (GWP). These were owing to that AWD irrigation reduced 38.3% CH4 emissions while increase 145.9% N2O emissions when compared to CF irrigation, and the low rate (25%) OFS only reduced CH4 emission by 29.4% while high rate (50%) only reduce N2O emission by 38.8% when compared to conventional inorganic nitrogen fertilizer (N180). Combined AWD and ON25 could maximize the reduction in GWP and yield-scaled GWP, which were reduce 58.0% and 52.5%, respectively, compare to the conventional water and nitrogen management (CF and N180). Furthermore, the structural equation modelling (SEM) indicated that the soil dissolved organic carbon (DOC) and rice aboveground biomass showed a significant positive effect on CH4 fluxes while soil NH4+ with a negative effect, and the soil NH4+, nitrification potential, denitrification potential significant affected N2O fluxes with a positive effect while DOC with a negative effect. These results investigated that 25% OFS rate for inorganic fertilizer could further reduce warming potential in AWD irrigation rice field.

Mitigation of Nitrous Oxide Emissions from Rice–Wheat Cropping Systems with Sub-Surface Application of Nitrogen Fertilizer and Water-Saving Irrigation

Management of nitrogen (N) fertilizer and irrigation can play a critical role to increase nitrogen use efficiency (NUE). However, the impacts of N application at the root zone via urea briquette deep placement (UDP) and water-saving irrigation alternate wetting and drying (AWD) on N2O emissions are not well-understood. A greenhouse study was conducted to investigate the impacts of UDP on N2O emissions, NUE, and grain yields of rice and wheat compared with broadcast prilled urea (PU). For rice, the effect of UDP was evaluated under continuous flooding (CF) and AWD, while the control (no N) and PU were tested only under CF. In rice, UDP under CF irrigation produced similar emissions to PU-CF, but UDP under AWD irrigation increased emissions by 4.5-fold compared with UDP under CF. UDP under CF irrigation increased (p &lt; 0.05) rice grain yields and N recovery efficiency (RE) by 26% and 124% compared with PU-CF, respectively. In wheat, UDP had no effects (p &gt; 0.05) on emissions compared with PU. However, it produced higher wheat grain yields (9%) and RE (35%) over PU. In conclusion, UDP under CF irrigation increases the RE and grain yields of rice without increasing N2O emissions, but the yield may reduce and N2O emissions may increase under AWD.

Growth, grain yield, and water productivity of different rice varieties in response to irrigation management techniques

Abstract The higher water consumption in the flooding irrigation system has challenged rice cultivation. Applying irrigation management techniques that help to save water and increase water productivity is necessary to deal with water shortage. We evaluated the growth, yield, water consumption, and water productivity responses in rice genotypes to irrigation management techniques. The experiment was arranged in a split-plot design with three replications at the Rice Research Institute of Iran, Mazandaran. The treatments were four rice varieties (Toloo, Tarom, Tisa, and Shiroudi) as main plots and six irrigation methods (continuous flooding irrigation (CFI) from transplanting to 20 days after 50% flowering (I1), CFI from transplanting to 15 days after 50% flowering (I2), CFI from transplanting to 10 days after 50% flowering (I3), CFI from transplanting to 5 days after 50% flowering (I4), CFI from transplanting to flowering stage (I5), and alternate wetting and drying (AWD) irrigation from transplanting to 20 days after 50% flowering (I6)) as sub-plots. The results showed that the Toloo genotype had the highest grain yield, lowest water consumption, and greatest water productivity compared with other studied genotypes. The I6 treatment with a slight reduction in yield (6% yield loss) was able to increase water-saving by 17.3%.

Study on the In-Field Water Balance of Direct-Seeded Rice with Various Irrigation Regimes under Arid Climatic Conditions in Egypt Using the AquaCrop Model

Crop growth models are cost-effective and user-friendly tools for decision-makers to develop efficient in-field management strategies. These models are particularly important in countries such as Egypt, where the risk of water scarcity is inevitable. The present study aimed to examine the in-field water balance of direct-seeded rice (Giza 178) under various irrigation regimes and arid conditions during two growing seasons (2019 and 2020). Four irrigation regimes, namely, continuous flood irrigation with a fixed water depth of 5 cm, and 3-, 6-, and 10-day irrigation frequencies (FI, 3IF, 6IF, and 10IF, respectively), were arranged in a randomized complete block design with three replicates. Then, the feasibility of using AquaCrop in simulating direct-seeded rice development and in-field water balance was assessed. Five statistical indicators, including normalized root-mean-squared error (NRMSE), index of agreement (d), coefficient of determination (R2), Nash–Sutcliffe efficiency coefficient (EF), and percent deviation (Pd), were used to evaluate the performance of AquaCrop. The field trial results demonstrated that both the 3IF and 6IF irrigation regimes were the best for achieving the highest biomass (21.0 t·ha−1, under 3IF), yield (9.8 t·ha−1, under 3IF), and saving irrigation water (18.3–22.4%, under 6IF), making them the best to apply in Egypt. Moreover, the AquaCrop simulation results showed a good correlation between the observed and simulated rice yield (Y) in both seasons (R2 = 0.99 and 0.98 in 2019 and 2020, respectively). AquaCrop showed excellent performance in simulating canopy cover (CC) and biomass (B) during both growing seasons (5.0 ≤ NRMSE ≤ 15.0, 0.97 ≤ d ≤ 0.99, 0.92 ≤ R2 ≤ 0.99, and 0.92 ≤ EF ≤ 0.99). In addition, the model showed acceptable performance in simulating in-field water balance components. Reasonably good model efficiency was recorded in simulating crop actual evapotranspiration (ETact). Meanwhile, the average Pd for percolation (P) was between −15.3% and 5.4% during both growing seasons. Overall, AquaCrop showed adequate accuracy in simulating CC, B, Y, ETact, and P but relatively low efficiency in simulating ETact and P under severe water scarcity. Therefore, AquaCrop may serve as a valuable tool for irrigation management and crop yield prediction even in arid regions, such as Egypt.

Nitrous oxide emissions from rice paddy: Impacts of rice straw and water management

AbstractTypically, organic amendment additions like rice straw (RS) are used in agriculture to improve soil quality. The application of RS may influence the production of methane and nitrous oxide (N2O), which may increase the amount of accessible nutrients and organic matter (OM). When compared to farmers' practices of continuous flooding irrigation (CFI), water management (WM) techniques like alternative wetness and dryness irrigation (AWDI) in paddy rice cultivation boost water use efficiency and may result in lower greenhouse gas (GHGs) emissions. A randomized complete block design (RCBD) was employed to evaluate the impacts of WM (CFI and AWDI), RS (15.0 and 30.0 ton ha−1), and their interaction (RS*WM) on the N2O emission and rice yield in a rice paddy calcareous soil. In comparison to control, a single application of RS at 15.0 and 30.0 ton ha−1 significantly reduced N2O emissions by 16.20% and 31.40% (p &lt; 0.01). AWDI regime increased N2O emissions by 67.0% in comparison to the CFI regime (p &lt; 0.01). According to two tailed Pearson correlation, the correlations between AWDI and N2O emissions in the days following rice planting were significantly positive at 0.01 levels. In AWDI regime, adding RS significantly reduced N2O emissions by 18.68% and 31.55% in 15.0 and 30.0 ton ha−1 added RS, respectively, compared to solo WM treatments (p &lt; 0.01). Both RS rates resulted in a considerable increase in biomass and rice grain while AWDI had no significant effect on them. Our study shows that AWDI saved 18.50% water in comparison with CFI regime.

Water Productivity and Harvest Index Response of Paddy Rice with Alternate Wetting and Drying Practice for Adaptation to Climate Change

The current water scarcity and world population increase cause the need for more food, pushing the demand on water resources due to crop production such as rice. Increasing agricultural water productivity by reducing the amount of irrigation water without affecting the yields, especially in paddy rice, is necessary. This is possible with alternate wetting and drying (AWD) irrigation. This study was conducted under greenhouse conditions at Tokyo University of Agriculture and Technology, Japan to evaluate the response of yield, water productivity and harvest index with different water regimes. The experiment was performed in pots with four water regimes as treatments and three replications, making 12 pots. The water regimes were continuous flooding irrigation as control and three AWD conditions—AWD5, AWD10 and AWD15—in which pots were irrigated when water reached 5, 10 and 15 cm soil depth, respectively, after the disappearance of surface ponding water. Yield components, harvest indexes and water productivity showed no significant difference (p &lt; 0.05) between irrigation treatments. In this research, as there is more than a 25% reduction in water use and only 6.4% in grain yield, AWD15 was considered the best irrigation practice among the other treatments. This study provides data reference for theoretical scientific knowledge and understanding of safe AWD practice for countries facing water shortages.

Effects of mild alternate wetting and drying irrigation and rice straw application on N2O emissions in rice cultivation

Abstract. The shortage of water resources and the decline in soil organic matter (SOM) are critical limiting factors affecting the improvement in rice productivity, while alternate wetting and drying (AWD) irrigation and recycling application of rice straw (S) are considered favorable mitigation measures. However, the impact of such measures on rice yield and greenhouse gas (GHG) emissions, especially nitrous oxide (N2O) emissions, needs to be further clarified to ensure that agronomic practices save water, conserve soil, and reduce GHG emissions. Therefore, we explored the effects of mild AWD irrigation combined with on-site rice straw recycling on N2O emissions and rice yield through rice pot experiments. This experiment included 2 irrigation methods (continuous flooding (CF) irrigation and mild AWD irrigation), 2 nitrogen (N) application levels (0 and 225 kg N ha−1) and 2 rice straw return levels (0 and 9000 kg ha−1), for a total of 10 treatments, and each treatment had 3 replicates. The 15N-urea and 15N-S were added to the soil. The results showed that N2O emissions were primarily affected by urea application and irrigation methods, with urea application being most important. Compared with CF irrigation, mild AWD irrigation increased cumulative N2O emissions, with an average increase of 28.8 %. In addition, adding rice straw to mild AWD irrigation further stimulated N2O emissions by 18.1 %. Under the condition of urea application, compared with CF irrigation, mild AWD irrigation increased the yield-scaled N2O emissions by 17.9 %, and the addition of rice straw further promoted the yield-scaled N2O emissions under mild AWD irrigation by 17.4 % but reduced the global warming potential (GWP) (methane (CH4) + N2O) by 62.9 %. Under the condition of urea application, compared with CF irrigation, mild AWD irrigation reduced the uptake of soil-derived N and aboveground biomass of rice but did not reduce rice yield. Therefore, mild AWD irrigation combined with rice straw return may be a promising agronomic method to maintain rice yield, reduce GHGs, and protect or improve soil fertility.