Water distributions of low-pressure sprinklers as affected by the maize canopy under a centre pivot irrigation system

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Selection of a suitable low-pressure sprinkler can be an effective measure to reduce energy consumption, wind drift and evaporation losses. The crop canopy often redistributes the applied water during sprinkler irrigation. Therefore, we investigated the water distributions above and below the canopy as well as their differences in Heermann and Hein uniformity coefficient (CUH) under three commonly used sprinkler types (Nelson D3000, Nelson R3000, and Komet KPT) and two growth stages of summer maize (6-leaf stage and tasselling stage) to evaluate the effect of crop canopy on the water distribution of low-pressure sprinklers. The variations in the soil water content (SWC) and Heermann and Hein uniformity coefficient of soil water content (CUHS) were investigated further at 1 h before, 1 h after, and 24 h. Additionally, the effects of growth indices and sprinkler types on CUH and CUHS values were analysed. Both the water application depths and CUH values above the canopy were significantly higher than those below the canopy and the differences above and below the canopy increased significantly with the growth of maize. The CUHS after irrigation mainly depended on the initial SWC and CUHS values but was minimally correlated with the plant height, leaf area index, and sprinkler application uniformity. Although the CUH above the canopy (78.1%) of D3000 was significantly lower than R3000 and KPT sprinklers (both exceeding 90%), the CUHS of D3000 reached more than 93% after irrigation. This result indicated that the effect of sprinkler application uniformity was not important as predicted, and a good CUHS would be achieved after canopy interception and soil water redistribution irrespective of sprinkler types. This study provides an insight into the selection of best low-pressure sprinklers in centre pivot irrigation systems.