Water Depletion Depth of Grain Sorghum and Sunflower in the Central High Plains

• Published in: Agronomy journal 2002-07, Vol.94 (4), p.936-943
• Main Authors: Stone, Loyd R., Goodrum, Dwayne E., Schlegel, Alan J., Jaafar, Mahmad Nor, Khan, Akhter H.
• Format: Article
• Language: English
• ISSN: 0002-1962; 1435-0645
• DOI: 10.2134/agronj2002.9360

In dryland agriculture of the central High Plains, water is often the primary factor influencing selection of crops and cropping systems. For improved water management, a greater percentage of precipitation during fallow must be stored and used in crop production. More efficient water use can be promoted via agronomic management such as extending the root zone by use of deep‐rooted crops. While sunflower (Helianthus annuus L.) has a reputation for deep rooting, grain sorghum [Sorghum bicolor (L.) Moench] is the dominant dryland row crop in western Kansas. Our objective was to contrast the depth of soil water depletion and end‐of‐season rooting depth of sorghum and sunflower. Rooting depth at end of season was measured by the core‐break method during a 3‐yr study near Tribune, KS, on a Ulysses silt loam soil (fine‐silty, mixed, superactive, mesic Aridic Haplustoll). Water content was measured to the 3.2‐m soil depth by neutron thermalization. The water depletion front advanced downward at greater rates and to deeper depths with sunflower (3.1 m) than with sorghum (2.5 m). Water depletion in the 2.2‐ to 3.3‐m soil depth zone was significantly more for sunflower (48 mm) than for sorghum (14 mm). End‐of‐season rooting depth was significantly greater for sunflower (3.03 m) than for sorghum (2.54 m). The faster advance of the water depletion front and greater depth of rooting of sunflower compared with sorghum are factors contributing to drought avoidance in sunflower and its ability to deplete water from deeper soil depths.