Relevance of sprinkler irrigation time of the day on alfalfa forage production

Nighttime sprinkler irrigation usually results in lower water losses and higher irrigation uniformity compared with daytime sprinkler irrigation due to lower wind speed. However, daytime sprinkler irrigation modifies the microclimatic conditions within the crop canopy which could result in improved crop growth. We studied during three years the effect of daytime and nighttime irrigation on the yield, N content, N uptake, water use efficiency, microclimate and canopy temperature of an alfalfa (Medicago sativa L.) crop irrigated with a solid-set sprinkler system in a semiarid Mediterranean climate. Two irrigation treatments were tested: daytime irrigation and nighttime irrigation. The same irrigation amount was applied in both treatments (552 to 757 mm year−1). The water losses of daytime irrigation (10%) tripled the water losses of nighttime irrigation (3%). In one year, daytime irrigation decreased the mean Christiansen coefficient of uniformity (CU) by 4% and the seasonal CU by 2%. Microclimatic and canopy temperature changes during sprinkler irrigation were higher for daytime irrigation as compared to nighttime irrigation. Daytime irrigation slightly reduced the soil water content of the surface layer (0-0.3 m). The actual seasonal crop evapotranspiration was slightly higher (+3.7%) in the daytime irrigation treatment compared to the nighttime irrigation treatment only in one of the years. The annual alfalfa forage yield (16 to 22 Mg ha−1), N content (3.16 to 3.38%), N uptake (514 to 740 kg ha−1) and water use efficiency (17.7 to 25.9 kg ha−1 mm−1) were not affected by the irrigation time of the day. Although nighttime sprinkler irrigation results in some water saving, daytime sprinkler irrigation of alfalfa can be performed if necessary.