Microclimatic and physiological changes under a center pivot system irrigating maize

The microclimatic (air temperature and vapor pressure deficit (VPD)) and physiological (canopy temperature and plant transpiration) changes due to center pivot sprinkler irrigation were monitored at a commercial plot of maize (Zea mays L.). Two treatments were considered: (a) moist, measurements taken at three spots on a transect when the pivot was running over it; (b) dry, measurements taken simultaneously at a fourth spot D, 270 m apart. A total of 34 irrigation events were monitored, seven of which included plant transpiration measurements. For the transpiration-measured irrigation events, significant (P = 0.05) reductions in the monitored variables for the moist treatment were observed for 0.6–2.1 h before, during and 0.5–2.4 h after the irrigation. The average decreases for the phase during were 1.8–2.1 °C for air temperature, 0.53–0.61 kPa for VPD, 3.1–3.8 °C for canopy temperature, and 0.22–0.28 mm h−1 (30–36%) for transpiration. Lower reductions were found for the phases before and after. The duration of the microclimatic changes decreased as the distance from the center of the pivot increased (from 3.9 to 2.2 h), but the duration of the physiological changes was similar in the different pivot arm portions (≈4 h). Microclimatic and physiological changes were higher in drier and warmer days. Transpiration reduction due to irrigation was higher as closer to the center of the pivot and represented 5–7% of the applied water. The estimated reduction of ET represented 1.5–1.8% of the applied water. The reduction of transpiration and ET is positive because it represents a reduction in irrigation requirements.