Sprinkler irrigation machines: effect of a growing maize canopy on water partitioning, drop characteristics, and energy dissipation

The self-propelled sprinkler irrigation machine is an extended irrigation system that has reduced its energy dependency in the last twenty years by replacing impact sprinklers with low-pressure emitters. The reduction in pressure operation changes the characteristics of the drop population and its impact on the soil. The crop canopy can also modify the energy reaching the soil. This study aims to contribute to the understanding of water partitioning, drop characteristics and energy impacting the soil in a growing maize canopy irrigated with a sprinkler machine. The results may provide valuable insights for optimizing irrigation practices and managing potential soil erosion risks in sprinkler irrigated maize fields. Measurements were performed in a field experiment, above and below the canopy at different maize heights. All measurements were taken at two points with two nozzle sizes (4.58 and 6.75 mm). Water partitioning and drop characteristics change as the canopy grows. The amount of throughfall decreases as the maize grows. An increase in the proportion of the smallest (< 1 mm) and largest (3–4 mm) drop diameters was measured as one moved deeper into the canopy. For a completely developed canopy, a reduction in specific power reaching the soil was observed for the 6.75 mm nozzle, but both a decrease and an increase were measured for the 4.58 mm nozzle, depending on the measurement location. The highest percentage of stem flow associated with the largest nozzle resulted in a greater protective effect of the canopy compared to the smallest nozzle. The balance between throughfall reduction, dripping, and splashing determines the ability of the canopy to mitigate soil impact energy. This study advances previous works on sprinkler irrigation by adding the variation of drop population characteristics not only as a function of canopy height but also as a function of irrigation time. In addition, this study incorporates the characterization of water application with irrigation machine emitters, which produce different drop populations than sprinkler solid-sets, allowing for a comparison between both systems.