Rooting front and water depletion depths in grain sorghnm and sunflower

Rooting front advance and rooting depth are factors to consider in selectin g a crop for effective use of stored soil water. Our objective was to compa re rooting front development (advance rate and maximum depth) and water dep letion depth, 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 Fluve ntic Hapludolls). Root development was quantified through multiple field sa mplings and the core-break method. Water content was measured to 3.05 in by neutron attenuation. Rooting front depths of the two crops were similar fr ont emergence to mid-June [0 to 20 d after emergence (DAE)], but from late June, sunflower roots were deeper than sorghum roots. Maximum rooting depth s were 1.85 in 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 i n 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 sorg hum. The faster advance rate and deeper depth of rooting aid sunflower in d rought avoidance and use of water from deeper soil depths.