Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/13/2011
Publication Date: 4/30/2012
Citation: Tolk, J.A., Evett, S.R. 2012. Lower limits of crop water use in three soil textural classes. Soil Science Society of America Journal. 76(2):607-616. Interpretive Summary: Different soils hold different amounts of water that a crop can use. A crop can use sometimes use more water in one soil than it can in another soil. There is a "lower limit" to the amount of water it can pull out of the soil. We can determine this lower limit amount either by measuring it in the field, or in the laboratory. We compared the field-measured lower limits of crop water use of sorghum, corn, and cotton grown in a clay loam, silt loam, and sandy loam, to soil lower limits that were measured in a laboratory. In four out of nine cases, there were significant differences between the field value and the laboratory value. For example, the lower limit for cotton measured in the field was much lower than that measured in the laboratory for the silt loam soil but not in the clay loam soil. It depended on both crop type and soil type.
Technical Abstract: Accurate knowledge of the amount of soil water available for crop use allows better management of limited water supplies. Using neutron scattering, we determined the mean lower limit of field soil water use (LL*F, m**3 m**-3) to a depth of 2.2 m at harvest (three seasons each) of short-season maize (Zea mays L.), grain sorghum [Sorghum bicolor (L.) Moench], and cotton (Gossypium hirsutum L.). The objective was to determine whether the laboratory-measured soil water content at -1.5 MPa matric potential (LL*-1.5, m**3 m**-3) for each soil textural class was representative of the LL*F of each crop. The crops were grown in monolithic cores of clay loam, silt loam, or sandy loam soil contained in lysimeters with a surface dimension of 1.75 m**2 and a depth of 2.4 m at Bushland, TX. For the 2.2-m profile, the LL*F of cotton was significantly smaller than the LL*-1.5 of the silt loam soil by 0.052 m**3 m**-3 and significantly smaller than the LL*-1.5 of the sandy loam soil by 0.016 m**3 m**-3. The LL*F of maize was significantly larger than the LL*-1.5 of the clay loam soil by 0.037 m**3 m**-3 and the LL*F of sorghum was significantly smaller than the LL*-1.5 of the silt loam soil by 0.045 m**3 m**-3. Of the nine soil and crop combinations, LL*F did not vary among seasons by more than 0.01 m**3 m**-3 in five soil and crop combinations but did vary by more than 0.01 m**3 m**-3 in four combinations due to differences in meteorological conditions among years. Crop type, soil textural class, soil chemical layers (e.g., calcium carbonate), and interannual variations in climate all affected the ability of a crop to use soil water up to and beyond LL*-1.5.