Maize hybrid response to sustained moderate drought stress reveals clues for improved management

Crop water productivity (CWP), irrigation water productivity (IWP), actual seasonal basal crop coefficient (K_ab), and actual crop evapotranspiration (ET_a) are essential parameters for accurate estimation of crop water requirement to prevent irrigation water waste. These parameters were evaluated by conducting three experiments using a drought-tolerant maize hybrid and a non-drought-tolerant (‘standard’) maize hybrid receiving 50, 100, and 150% of the recommended optimal nitrogen (N) fertilizer rate and grown under well-watered conditions, drought stress from the 14 leaf collar maize phenological stage (V14) to maize physiological maturity (R6), and drought stress from the blister maize phenological stage (R2) to R6. Across hybrids, ET_a decreased with increased duration of drought stress. The drought-tolerant hybrid had 7 and 8% greater CWP and IWP, respectively, compared to the standard hybrid when drought stress began at V14. Mid-season K_ab was 1.08, 0.89, and 0.73 under well-watered conditions and when drought stress began at R2 and V14, respectively. These results reveal that (i) maize achieved more effective physiological acclimation with earlier exposure to drought stress, (ii) grain yield of the drought-tolerant hybrid was unchanged by earlier, compared to later, onset of drought despite a 10% decrease in ET_a, and (iii) two phases of acclimation were identified: Maize K_ab declined upon exposure to drought but stabilized as the crop acclimated.