Contrasting Strategies of Water Use: Seasonal Root Growth and Soil Water Depletion in Maize and Sunflower Under Deficit Irrigation.

Quantifying root growth and soil water depletion in response to deficit irrigation is key to understanding crop ET under deficit irrigation as well as modeling crop water use across the season.  We examined seasonal root growth and distribution patterns using a minirhizotron camera in maize and sunflower grown under seven drip irrigation treatments (full + 6 deficit).  In both crops, root growth continued through reproduction.  Maize depleted the soil water profile more slowly than sunflower, which depleted soil water deep in the profile in all treatments.  Under increased deficit irrigation, maize increased root production per leaf area and the percentage of roots deep in the soil profile to a larger degree than sunflower.  In contrast, sunflower generally produced more roots than maize across all treatments.  Although sunflower slightly increased root production under increased deficit irrigation, root distribution of sunflower through the soil profile did not shift.  Maize appears to leave more water in the profile in contrast to sunflower, which extracts soil water to low levels to maintain high transpiration rates, growing within narrow margins of embolism resistance and wilting.