Rooting Front and Water Depletion Depths in Grain Sorghum and Sunflower

Abstract

Rooting front advance and rooting depth are factors to consider in selecting a crop for effective use of stored soil water. Our objective was to compare rooting front development (advance rate and maximum depth) and water depletion depths of grain sorghum [Sorghum bicolor (L.) Moench] and sunflower (Helianthus annuus L.) in a field experiment. The study was near Manhattan, KS on Eudora silt loam soil (coarse‐silty, mixed, superactive, mesic Fluventic Hapludolls). Root development was quantified through multiple field samplings and the core‐break method. Water content was measured to 3.05 m by neutron attenuation. Rooting front depths of the two crops were similar from emergence to mid‐June [0 to 20 d after emergence (DAE)], but from late June, sunflower roots were deeper than sorghum roots. Maximum rooting depths were 1.85 m in sorghum and 2.49 m in sunflower (means of 2 yr). From 20 to 60 DAE, rooting front depth increased 25 and 41 mm d−1 in sorghum and sunflower, respectively. From 60 to 90 DAE, rooting front depth increased 8 and 6 mm d−1 in sorghum and sunflower, respectively. Net seasonal water depletion was greater in sunflower plots than in sorghum plots (by 103 mm in 1985 and 112 mm in 1986). Sunflower roots advanced downward from 0 to 60 DAE at a rate and depth 46 and 35% greater, respectively, than that of sorghum. The faster advance rate and deeper depth of rooting aid sunflower in drought avoidance and use of water from deeper soil depths.