Resumen: El agua es un factor limitante para la expansión del cultivo de arroz en Uruguay. Durante las zafras 2010-2011, 2011-2012 y 2012-2013 se evaluaron diferentes alternativas de manejo del riego durante la etapa vegetativa del cultivo de arroz y su efecto sobre el rendimiento y el consumo de agua. El objetivo del estudio fue hacer un uso más eficiente del agua y aumentar su productividad. Se evaluaron tres alternativas de riego con inundación continua: inundados a los 15, 30 (testigo) y 45 días después de la emergencia (IC15, IC30 e IC45); y dos alternativas de riego controlado: lámina variable (LV) y riego restringido (RR). Los mayores rendimientos se registraron en los tratamientos IC15, IC30 y LV (10592, 10454 y 10189 kg ha-1, respectivamente) seguidos por los tratamientos IC45 y RR (9653 y 9287 kg ha-1, respectivamente). El menor consumo de agua de riego se obtuvo en el tratamiento RR (6568 m3 ha-1). La productividad del agua de riego osciló entre 1,18 (IC45) y 1,46 kg m-3 (RR). Este estudio demuestra que hay estrategias de manejo del riego en arroz que pueden reducir significativamente los consumos de agua logrando una alta productividad de la misma. Sin embargo, los rendimientos obtenidos determinan la necesidad de profundizar los estudios en alternativas de riego controlado, de manera que las restricciones hídricas generadas no impliquen una disminución en la productividad del cultivo.

Summary: Water is a limiting factor for the expansion of rice crop in Uruguay. During the seasons 2010-2011, 2011-2012 and 2012-2013 the effect of different irrigation management alternatives during the vegetative stage of rice on yield and water use were evaluated. The objective of this study was to improve water use efficiency and increase crop water productivity. Three continuous flooding treatments: flooding 15, 30 (control) and 45 days after emergence (CF15, CF30 and CF45), and two controlled irrigation treatments: intermittent irrigation (II) and alternate wetting and drying (AWD) were evaluated. Higher yields were obtained in treatments CF15, CF30 and II (10592, 10454 y 10189 kg ha-1, respectively), followed by CF45 and AWD (9653 y 9287 kg ha-1, respectively). AWD treatment had the lowest irrigation water use (6568 m3 ha-1). Mean irrigation water productivity ranged from 1.18 (CF45) to 1.46 kg m-3 (AWD). This study demonstrates that there are irrigation strategies that can significantly reduce irrigation water use while reaching high water productivity values. However, the yields obtained determine the need to deepen the studies in controlled irrigation alternatives, so that the water restrictions generated do not imply a decrease in crop productivity.

ABSTRACT Water management impacts both methane (CH4) and nitrous oxide (N2O) emissions from rice paddy fields. Although controlled irrigation is one of the most important tools for reducing CH4emission in rice production systems it can also increase N2O emissions and reduce crop yields. Over three years, CH4 and N2O emissions were measured in a rice field in Uruguay under two different irrigation management systems, using static closed chambers: conventional water management (continuous flooding after 30 days of emergence, CF30); and an alternative system (controlled deficit irrigation allowing for wetting and drying, AWDI). AWDI showed mean cumulative CH4 emission values of 98.4 kg CH4 ha−1, 55 % lower compared to CF30, while no differences in nitrous oxide emissions were observed between treatments ( p > 0.05). No yield differences between irrigation systems were observed in two of the rice seasons ( p > 0.05) while AWDI promoted yield reduction in one of the seasons ( p< 0.05). When rice yield and greenhouse gases (GHG) emissions were considered together, the AWDI irrigation system allowed for lower yield-scaled total global warming potential (GWP). Higher irrigation water productivity was achieved under AWDI in two of the three rice seasons. These findings suggest that AWDI could be an option for reducing GHG emissions and increasing irrigation water productivity. However, AWDI may compromise grain yield in certain years, reflecting the importance of the need for fine tuning of this irrigation strategy and an assessment of the overall tradeoff between relationships in order to promote its adoption by farmers.