Irrigation Strategies for Tall Fescue Under Grazing in a Humid Subtropical Temperate Climate

During the last 10 years, there has been a rapid expansion of irrigation in pastures in Uruguay. It is necessary to define the irrigation management under grazing conditions to achieve the best balance between productivity and the sustainability of natural resources. A trial was established with the drought-sensitive Festuca arundinacea Schreb. cultivar INIA Aurora under grazing. During two and a half years, the following treatments were evaluated: frequent irrigation (T1), which was applied whenever 30% of the available water was depleted; spaced irrigation (T2), which was applied whenever 65% of the available water was depleted and rainfed treatment, which only received rainwater. The experimental design was a randomised complete block with four replications. Grazing was carried out every time the tall fescue reached 2.5 leaves. There was a significant difference in annual dry matter yield between the irrigated and rainfed treatments, but the irrigated treatments did not differ from each other. The average dry matter yield of irrigated treatments was 41% and 56% higher than the rainfed treatment for the first and second year of pasture, respectively. The spaced irrigation management resulted in a 38% saving in pumped water compared to frequent irrigation. However, when considering water productivity as a selection criterion, frequent irrigation would be the recommended irrigation strategy. Irrigation increases soil compaction in a grazing system, and with frequent irrigation management, this effect persists even up to 10 cm of soil depth.