Water productivity under strategic growth stage-based deficit irrigation in maize

Water shortages are responsible for the greatest crop losses around the world and are expected to worsen. In arid areas where agriculture is dependent on irrigation, various forms of deficit irrigation management have been suggested to achieve high yields with less water used by the crop (i.e. evapotranspiration, ET). This study of maize evaluated twelve treatments with varying levels of deficit irrigation during late vegetative and maturation (grain filling) growth stages in semi-arid Northern Colorado. In particular, application of greater deficit during the late vegetative state with full or nearly full ET during the rest of the season consistently resulted in yield similar to full ET treatments while saving approximately 15-17% of ET. Maize given 40% of full ET during the late vegetative period had slightly reduced leaf area index (LAI) with significant leaf curling, thus reduced light interception during vegetative growth. However, when plants were fully watered during anthesis, all treatments had full canopy cover with no differences in light interception. The efficiency of photosystem II (quantum yield) declined with water stress but recovered with re-watering. The ability of photosystem II and light interception to recover after stress when well-watered suggests that reductions in biomass and yield resulted from stomatal closure, reduced photochemistry, or loss of xylem conductance that was temporary. With little indication of permanent decline in carbon assimilation after reducing ET in vegetative stages, maize appears able to achieve high grain yield if soil water is readily available during the reproductive and maturation stages. However, plants given full or nearly full irrigation during the entire vegetative period followed by stress later on during the maturation period, had dramatically greater yield loss than ET savings. Thus, while strategic deficit irrigation might maintain yield with less water, it may be especially important for buffering crops against yield losses due to end of season water shortfalls in water limited environments.