Global water scarcity demands urgent adoption of water-conserving practices in irrigated rice production. This field study, conducted in 2019 in Babolsar, northern Iran, evaluated the potential of deficit irrigation strategies delivered through a drip tape system to conserve water and sustain productivity in the Binam rice variety. Irrigation management treatments were based on maintaining soil water potential thresholds of 10, 30, and 60 kPa, applied either over the entire root zone (regulated deficit) or alternately to half of the root system (partial root-zone drying), alongside full drip irrigation and conventional flood irrigation as controls. Flood irrigation produced the highest grain yield (6442 kg ha⁻¹) but required the most water (10886 m³ ha⁻¹). In contrast, alternate partial drying at the driest threshold (60 kPa) achieved the greatest irrigation water productivity (1.39 kg m⁻³), a 135.6

CONTEXT: Irrigated paddy fields are major contributors to methane (CH4) emissions, significantly impacting global warming. Flood irrigation, the traditional method for rice cultivation, significantly increases water consumption and CH4 emissions. OBJECTIVE: The primary objective of this study was to quantify the benefits of deficit irrigation in reducing CH4 emissions and maintaining yield compared to traditional flood irrigation using a systems analysis approach. METHODS: The field study was conducted from May to August in both 2015 and 2016 at the Rice Research Institute in Amol, northern Iran. The site has a warm temperate climate, with the soil characterized as silty clay loam. The data collected during these two years were used for the calibration and evaluation of the CSM-CERESRice model. Calibration was performed using the data collected in 2016 while the model's performance was evaluated using data collected in 2015. Following model calibration and evaluation, a seasonal analysis was employed to assess alternative management practices for single growing seasons. This analysis feature of DSSAT allowed us to evaluate alternate management scenarios with the model using 35 years of long-term historical daily weather data from 1984 to 2018 obtained from a local weather station. RESULTS AND CONCLUSIONS: The simulation revealed that early rice planting, in April or May, yielded the highest production and the lowest CH4 emissions, when using the direct seeding method. This strategy resulted in a 15 % increase in yield, 13 % better irrigation efficiency, and a 9 % reduction in CH4 emissions compared to transplanting. Among tillage systems, no-tillage further reduced CH4 emissions by 29 % without compromising yield or irrigation efficiency. Although sowing depth did not significantly affect CH4 emissions or yield, an optimal depth of 10-15 cm was identified. Additionally, maintaining a plant population of 10 transplants per hill exhibited the lowest CH4 emissions compared to higher plant populations. Higher nitrogen fertilization rates increased both yield and CH4 emissions. In conclusion, the best approach among different strategies was early cultivation for direct-seeded rice coupled with a nitrogen fertilizer rate of 250 kg ha- 1 , resulting in both the highest yield and the lowest emissions simultaneously. SIGNIFICANCE: The findings from this study offer a comprehensive exploration, identifying specific agronomic practices that optimize rice cultivation by enhancing yield, conserving water, and significantly reducing CH4 emissions, thereby providing actionable insights for policymakers and farmers in fostering sustainable agriculture.

This experiment aims to study the effect of water-saving irrigation on rice production and methane emissions. Three irrigation methods, that is, flooding irrigation, deficit irrigation (DI) and alternate partial root-zone drying (APRD), were employed in a 2-year field trial. The experiment was conducted in a randomized complete block design with three replications. For the DI and APRD treatments, plots were not irrigated until the soil matric potential reached -10 (DI10 and APRD10), -30 (DI30 and APRD30) and -60 kPa (DI60 and APRD60). In the APRD treatments, two adjacent furrows of each plant row were alternately irrigated in consecutive irrigation events. The DI and APRD treatments did not affect yield components when the soil matric potential was -10 kPa. Applying APRD treatments increased irrigation water productivity by 45%, 51% and 31% for soil matric potentials of -10, -30 and -60 kPa, respectively. On average, water stress treatments reduced methane emissions by 78% compared to flooding treatment. On average, the APRD treatments decreased the water input by 10% compared with the DI treatments while achieving a 2.5% higher yield. This is the first study to outline the effect of APRD on methane emissions and rice production. These findings suggest that APRD could be a valuable strategy to mitigate methane emissions without risking rice yield reduction.

While paddy fields produce a high yield, they also require a large amount of water and produce a significant amount of methane. Therefore, the adoption of water-saving irrigation techniques for rice cultivation is critical. Furrowed rice farming may be a viable alternative to paddy rice cultivation. The objective of the present study was to evaluate the impact of alternate partial root-zone drying irrigation on rice yield, milled rice quality, and cooking quality under furrow rice cultivation. A two-year field trial was conducted on a local rice cultivar, Tarom Hashemi, in 2015 and 2016. Seven water regimes, including three levels of regulated deficit irrigation (RDI), three levels of alternate partial root-zone drying irrigation (APRDI), and conventional flooding irrigation (CFI), were used in this study. In RDI and APRDI treatments, plots were irrigated when soil matric potential had reached −0.1 (RDI1 and APRDI1), −0.3 (RDI3 and APRDI3), and −0.6 bar (RDI6 and APRDI6). RDI1 and APRDI1 treatments produced milled rice yield similar to the CFI, while irrigation water productivity (IWP) was significantly higher by 22.9% and 45.7%, respectively. Regardless of the soil water potential, the IWP in APRDI treatments was 16% higher than that of RDI treatments. Severe water stress (RDI6 and APRDI6) caused a marked increase in amylose content and alkali spreading value of milled rice resulting in improved cooking quality. Nitrogen uptake in APRDI treatments was 2% higher than that of RDI treatments. On average, methane emission per milled grain yield declined by 77.9% and 78.7% in RDI and APRDI treatments, respectively. Our data indicate that the expensive and laborious practice of puddling can be avoided to increase water productivity and improve rice quality without sacrificing yield. The results also show that furrow rice cultivation could significantly reduce the methane emission contribution of rice production.