Combined effect of technical, meteorological and agronomical factors on solid-set sprinkler irrigation: I. Irrigation performance and soil water recharge in alfalfa and maize

In this work, maize (Zea mays L.) and alfalfa (Medicago sativa L.) were irrigated in two adjoining plots with the same sprinkler solid-set system. Irrigation was evaluated between four sprinklers in the central position within each plot, above the canopy with pluviometers and in the soil with a FDR probe. Maize and alfalfa were simultaneously irrigated under the same operational and technical conditions during two seasons: in 2005, the solid-set irrigation system layout was rectangular, 15 m between sprinklers along the irrigation line and 15 m among lines (R15 × 15), and the seasonal irrigation applied according to the crop evapotranspiration (ET_c); in 2006, the solid-set layout was R18 × 15 and the seasonal irrigation was around 30% lower than the ET_c. The irrigation depth above the canopies (ID_C) and the soil water recharge after irrigation (RW) were monitored using a 3 m × 3 m grid (25 points in 2005 and in 30 points in 2006). For maize, RW was assessed both in the lines of plants (CL) and between the lines (BCL).The average values of ID_C were similar between crops during both seasons but the uniformity (CUC) of the ID_C noticeably depended on the crop: the differences were greater between crops than between sprinklers spacings (R15 × 15 and R18 × 15). The CUC of ID_C, the RW and the CUC of RW were greater for alfalfa than for maize. The CUC of ID_C was greater than the CUC of RW for both crops. The RW was significantly related with the ID_C throughout the irrigation season for alfalfa. The correlation was weaker for maize, with important differences between positions and between growth stages. At the beginning of the season, the RW significantly correlated with the ID_C, both in the CL and BCL positions. However, the correlation weakened when the maize grew, especially in the CL, because the maize plants redistributed the water.The results show that the height and canopy architecture of the crop must be considered in the analysis of the sprinkler water distribution as factors influencing the irrigation performance.