En regiones de clima templado y húmedo como Uruguay el riego estabiliza y aumenta los rendimientos de los cultivos estivales, suplementando las precipitaciones. El riego a demanda tiene mayor consumo de agua, afectando la sostenibilidad del sistema de producción por el uso ineficiente de los recursos, y es ambientalmente negativo (uso excesivo de agua dulce y energía para su extracción). Es necesario evaluar alternativas de riego deficitario que aumenten la productividad del agua riego. Para ello se evaluaron tres láminas máximas de reposición: (T2) 3 mm día-1, (T3) 6 mm día-1, (T4) 9 mm día-1, y (T1) testigo sin riego, (solo agua de lluvia), sobre la producción de maíz, para definir estrategias de riego más eficientes. Los resultados indican que existe respuesta a diferentes niveles de riego deficitario. Cuando las precipitaciones fueron superiores al promedio, su mala distribución durante el ciclo del cultivo generó déficit hídrico en momentos puntuales, afectando el rendimiento. El T1 y T2 no cubrieron la etc durante el Periodo Crítico y llenado de grano, causando menores rendimientos. El T3 y T4 dieron rendimientos mayores y en el promedio de tres años fueron diferentes significativamente. El T3 no siempre cubrió la etc, pero la reserva del suelo y las precipitaciones contribuyeron para cubrirlo, ahorrando casi 20 % de agua de riego respecto a T4. Sin embargo, los indicadores de productividad del agua (eua, euar) muestran que T4 es mejor estrategia de riego, aunque realice menor aprovechamiento de las precipitaciones y del agua del suelo.

In regions with a temperate and humid climate, deficit irrigation improves the profitability and sustainability of production systems, when properly implemented. It is necessary to generate knowledge on the response of crops to deficit irrigation. Aiming to improve the design and management of irrigation equipment used in soybean cultivation in Uruguay, an experiment was proposed where three maximum depths of irrigation replacement (3 mm, 6 mm and 9 mm day-1) and non-irrigated control were evaluated. A randomized complete block design was used, with four treatments and four replications. Drip irrigation was applied, which allowed a good adjustment of the different irrigation depths used and reduced the experimental area. Non-irrigated and 3 mm suffered water stress from V10 to grain filling, producing lower yields. The 6 mm treatment yielded the same as the 9 mm in Year 1, but lower in Year 2. This study indicates that irrigation is necessary when rainfall is less than the average for the region or its distribution is inadequate. The 9 mm treatment showed the highest water productivity (WUE: 0.86 Kg m-3) and irrigation (IWUE: 0.54 Kg m-3), with less use of rainfall, compared to 6mm.

The high water demand of rice cultivation is mainly due to flood irrigation, which requires large volumes not only to meet evapotranspiration needs, but also due to losses from percolation, lateral seepage, and surface runoff. In addition to lowering water use efficiency, surface runoff may transport nutrients. This study aimed to calibrate and validate a daily water balance model to estimate surface runoff losses across three rice-growing seasons. During the first two seasons, different model components were calibrated by comparing simulated and observed water depths. In the final season, the calibrated model was validated using direct runoff measurements obtained from weirs and flowmeters. Results showed strong agreement between model estimates and direct measurements of water depth and surface runoff. Linear regression models showed good fit, with coefficients of determination (R²) above 0.80 for water depth and 0.79 for runoff. A validated daily water balance model, combined with periodic monitoring of water depth, proved to be a reliable tool for estimating surface runoff during the rice-growing season. Total runoff—from irrigation, rainfall, and final drainage—represented between 7.5% and 18% of the total water input. This approach offers a practical tool for improving irrigation water management and understanding runoff-driven nutrient transport.

The AquaCrop model allows evaluating and designing irrigation strategies that improve the use of irrigation water. The objective of this research was to calibrate and validate the AquaCrop model for maize to the climatic conditions of southern Uruguay, with different irrigation water management. This model was calibrated and validated for corn using experimental data from irrigation trials with different deficit levels in three seasons, 2015-16 and 2016-17 (calibration) and 2014-15 (validation). Three maximum irrigation depths were evaluated: 3, 6 and 9 mm day-1, and rainfed (rainfall only). The crop was parameterized for local conditions and water stress coefficients were adjusted. The calibration simulated the yield, biomass and soil moisture in the irrigated treatments with good performance. All the statistic indexes used to evaluate the adjustment between the observed and simulated data model indicated a good model performance, with the exception of the efficiency coefficient of the Nash-Sutcliffe (EF) model. The model underestimated the yield in the rainfed treatment (EF of -0.52) when root depth was limited to 0.7 m. However, the test soil allowed for greater radical exploration than the initially used. At 0.90 m root depth, the model was good at simulating the yields in the rainfed treatment, mainly in dry years (EF of 0.79). The model predicts the yield with good adjustment in different irrigation and rainfall situations if the stress coefficients are adjusted and the crop is properly parameterized, mainly the root depth.

La alfalfa es una especie forrajera muy utilizada en Uruguay en ganadería intensiva y lechería. El riego suplementario permite mitigar los efectos negativos del cambio climático, aumentando y estabilizando la productividad de las pasturas. Es necesario evaluar su efecto conjunto con el pastoreo. Se evaluaron dos umbrales de riego, con entrada de animales. Los tratamientos fueron: riego frecuente (30% agotamiento), riego espaciado (65% agotamiento) y secano. El diseño experimental fue de bloques completos al azar, 30 meses de evaluación. La productividad promedio anual de la alfalfa regada fue de 25333 y 23177 kg MS ha-1, primer y segundo año de evaluación, respectivamente. La producción acumulada (30 meses) no mostró diferencia significativa entre los tratamientos regados, pero sí entre regados y secano. En el último verano-otoño, la productividad de todos los tratamientos cae a 8660 kg MS ha-1 (regados) y 1756 kg MS ha-1 (secano). Las productividades estacionales indican la conveniencia de regar la alfalfa en verano, ya que el rendimiento aumentó 43% en el segundo año y 4,3 veces más en el último año. Además, luego de transcurrir la sequía extrema del verano, en el otoño siguiente los regados rindieron 7 veces más que el secano. El manejo con riegos espaciados y láminas de riego que no devuelven el suelo a su capacidad de campo aumenta la efectividad de las precipitaciones, ahorrando agua y energía destinada al riego. La densidad aparente aumentó hacia el final del experimento a consecuencia del pastoreo, sin embargo, no hubo diferencia entre los manejos de riego evaluados.

In regions with temperate and humid climate such as Uruguay, supplementary irrigation stabilizes and increases crop yields. Irrigation on demand generates higher water consumption, which affects production system sustainability due to inefficient use of resources. In order to determine environmentally and economically more sustainable irrigation strategies, three maximum irrigation depths were evaluated in field experiment, (T2) 3 mm d-1, (T3) 6 mm d-1, (T4) 9 mm d-1 and (T1) control without irrigation, on corn and soybean production. Performance differences were observed in both crops at different water deficit levels. When precipitation (PP) was higher than average, its poor temporary distribution generated water deficit at specific times, affecting yield. T1 and T2 did not cover the crop evapotranspiration (ETc) during the critical period and grain filling, which lowered yields. T3 and T4 gave higher yields and in the three years average they were significantly different. T3 did not always cover the ETc, but the soil reserve and PP contributed to cover it, saving irrigation water. The AquaCrop model was calibrated for maize and different irrigation strategies were evaluated. The calibrated model simulated well yield, biomass and soil moisture in the irrigated treatments. In T1, the model underestimated the yield. The soil allowed for further root exploration. At 0.90 m depth, the model simulated well the yield in T1, mainly in the dry year. The model predicts the yield with a good adjustment at different irrigation and PP situations if the stress coefficients are adjusted and the crop is properly parameterized. Finally, T1, three maximum irrigation depths (3, 6 and 8 mm net) and three irrigation management (depleting 10 mm, depleting 50 % of readily available water (RAW) and depleting 100 % of RAW) were evaluated in maize with AquaCrop. The productive variables, irrigation requirement, energy demand and partial income analysis were analyzed, considering a maize crop irrigated by central pivot. It is concluded that 5 mm net gives returns and income similar to 8 mm net, without considering investment costs. Regarding management, depleting 100 % of the RAW has higher water productivity, but it is risky in dry years; however, it is feasible to vary the strategy depending on the climatic perspectives of each year.