Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/18/2004
Publication Date: 1/1/2005
Citation: Moroke, T.S., Schwartz, R.C., Brown, K.W., Juo, A.S. 2005. Soil water depletion and root distribution of three dryland crops. Soil Science Society of America Journal. 69:197-205.
Interpretive Summary: Development of dryland cropping strategies with improved yield potential and stability requires knowledge of the depth to which water is extracted by crops from the soil as well as changes in crop water use throughout the season. The objective of this study was to characterize root growth and associated water depletion patterns of cowpea (black-eyed peas), sorghum and sunflower under no-tillage and stubble mulch tillage systems in a clay loam soil. Root growth of sorghum and sunflower near the soil surface increased rapidly after emergence but thereafter declined. However at greater depths, rooting density of these crops increased throughout the growing season. Sunflower initially depleted soil water at a greater rate than sorghum; however as sorghum reached maturity, differences in soil water depletion between these two crops were not evident. Water contents at the end of the growing season were 1 to 3.7 inches greater under cowpea as compared to sorghum but these gains were partially offset by greater evaporative losses under cowpea during the winter. No-tillage plots exhibited deeper rooting and greater water extraction at soil depths exceeding 4 feet. Results suggest that a rotation of cowpea with sorghum or sunflower would permit the stratified use of soil water and that storage and crop use of water deep in the soil profile would be optimized under no tillage.
Technical Abstract: Characterization of plant uptake of soil water at different points in time and space are important in evaluating seasonal water use as well as rotational dryland cropping strategies. The objective of this study was to characterize root length density and soil water depletion patterns of cowpea [Vigna unguiculata (L.) Walp], grain sorghum [Sorghum bicolor (L.) Moench] and sunflower (Halinthus annuus (L.)] under no tillage (NT) and stubble mulch tillage (SMT) systems in a Torrertic Paleustoll. Root length density (RLD) of crops was measured from scanned images of washed root samples obtained from soil cores extracted several times during each of two growing seasons. Soil water contents were measured with a neutron moisture meter to a depth of 2.3 m at weekly intervals throughout each growing season. The RLD's of sorghum and sunflower near the soil surface increased rapidly after planting but thereafter declined, whereas subsoil RLD increased throughout the growing season. Sunflower initially depleted soil water at a greater rate than sorghum, however as sorghum reached maturity, differences in soil water content between these two crops were not significant (P>0.05) over the soil profile. Residual water contents at the end of the growing season were 28 to 93 mm greater (P<0.05) under cowpea as compared to sorghum but these gains were partially offset by lower winter fallow efficiencies under cowpea. As compared with the other crops, most of the additional residual water under cowpea was confined to soil depths between 0.5 and 1.7 m. Relatively high water depletion rates at soil depths of 1.0 to 1.8 m indicated that this region was an important source of stored water for sorghum and sunflower later in the growing season. Deeper rooting and greater soil water extraction below 1.2-m depth were observed for NT as compared with SMT (P<0.05). Results suggest that a rotation of cowpea with sorghum or sunflower would permit the stratified use of soil water and that the storage and crop use of water deep in the profile would be optimized under NT.