Root distribution, soil water extraction patterns, and wateruse efficiency of selected dryland crops under differing tillage systems

In dryland regions, precipitation is not always used most efficiently. Combining the use of drought-adapted, early maturing crops with reduced tillage practices in dryland cropping systems can increase soil water storage, water-use efficiency and crop yields. The objective of this study was to evaluate soil water use by cowpea [Vigna unguiculata (L.) Walp], grain sorghum [Sorghum bicolor (L.) Moench], and sunflower ( Helianthus annuus L.), characterize their root distribution and soil water extraction patterns, and simulate evapotranspiration and soil water content under dryland sorghum using Energy and Water Balance (ENWATBAL) model. The study was conducted at Bushland, Texas on Pullman clay loam soil. The experimental design was a split plot with no tillage (NT) and stubble mulch tillage (SMT) as main plots and crops were assigned to subplots with three replicates. Soil water content to a depth of 2.3 m was measured by neutron scattering technique to estimate weekly soil water use during the growing season in 2000 and 2001. Crop root length densities were obtained from scanned images of roots from extracted cores. Soil water content at planting was significantly greater under NT compared with SMT. However, total soil water content at the end of the growing season was greater under cowpea compared with sorghum and sunflower. Seasonal evapotranspiration was greater under sorghum and sunflower compared with cowpea. Sorghum and sunflower had greater rooting depths as compared with cowpea. Soil water was extracted from deeper soil depths under sorghum and sunflower and this agreed with greater root length density at deeper depths for these two crops. Soil water was extracted from deeper soil depth under NT compared with SMT. At least 80 percent of root lengths of crops studied were in the upper 90 cm of the soil. Compared with measured data, ENWATBAL adequately simulated evapotranspiration of dryland grain sorghum under dryland conditions. Simulated and measured soil water content profiles differed because of differences in field and laboratory determined soil hydraulic functions.