FIGURE 2.

The production of root length and its distribution for fully and deficit irrigated maize and sunflower over the 2012 growing season in minirhizotron windows at the USDA-ARS Limited Irrigation Research Farm in Greeley, CO, USA (40.45°, -104.64°, 1430 m). Root growth is expressed in terms of root length per viewing area of minirhizotron window for two crops contrasting in hydraulic strategies grown under full and deficit irrigation. Total annual root growth in viewing windows down to 100 cm (A) as well as in 10 cm increments of soil depth (B) are given. Each bar and point represents root growth averaged among four minirhizotron tubes per treatment, with each tube installed in a different treatment plot. Soil at the site is a sandy loam. Annual precipitation is approximately 350 mm. Irrigation is applied with pressure-compensated surface drip. Deficit irrigation is applied to achieve a targeted 40% of full evapotranspiration (ET) irrigated treatment during deficit periods in late vegetative and maturation growth phases (V7-V21 and R3-R6 in maize; V8-R2 and R6-R9 in sunflower).