Lower Limits of Water Use by Cotton, Maize, and Grain Sorghum in Three Great Plains Soils.

            Accurate knowledge of the amount of soil water available for crop use helps agricultural producers select cropping and irrigation management strategies that maximize the yield of crops.  Using neutron attenuation, we measured the lower limits of soil water content (LL) at harvest (three seasons each) of short-season maize (Zea mays L.), grain sorghum [Sorghum bicolor (L.) Moench], and cotton (Gossypium hirsutum L.) grown in lysimeters containing monoliths of Pullman clay loam (fine, mixed, superactive, thermic Torrertic Paleustoll), Ulysses silt loam (fine-silty, mixed, mesic Aridic Haplustoll), or Amarillo sandy loam (fine-loamy, mixed, thermic Aridic Paleustalf).  The objectives were to compare a crop’s LL to depth of water (mm) held at ‑1.5 MPa measured by the pressure plate technique (LL_‑1.5mm) among soil types and to compare the LL of crops within a soil type.  The depth of water in a 2.2-m profile at LL (LL_mm) in the clay loam averaged 448(±7) mm for cotton, 533(±18) mm for maize, and 473(±34) mm for sorghum and profile water content at LL_-1.5mm was 425(±33) mm.  In the silt loam, LL_mm was 272(±7) mm for cotton, 358(±27) mm for maize, and 289(±12) mm for sorghum and LL_-1.5mm was 343(±13)  mm.  The LL_-1.5mm was 286(±20) mm in the sandy loam; and LL_mm was 249(±31) mm for cotton, 312(±14) mm for maize, and 260(±15) mm for sorghum.  Crop specific LL values may also have been impacted by variations in climate among crop years and the presence of the calcium carbonate horizon in the Amarillo and Pullman soils.  Knowledge of the lower limits of water use by crops in a particular soil not only allows producers to understand crop yield and water use relationships, but it is also important for the management of irrigation water supplies.