PLANT WATER RELATIONS AND GROWTH OF COWPEA CULTIVARS SUBJECTED TO VARYING DEGREES OF WATERLOGGING

There is potential in tropical regions to include cowpea (Vigna unguic ulata (L.) Walp.) in rice (Oryza sativa) based cropping systems, espec ially during the post-monsoonal dry season. The plant water relations, and root and shoot growth of two cowpea cultivars (IT82D-889, early m aturing, and TVX1948-012F, medium maturing) were compared in saturated and drier soil moisture regimes on an isohyperthermic, clayey, Typic Tropudalf soil by using a line-source sprinkler differential irrigatio n system. Saturated soil reduced total dry matter accumulation, plant height, crop growth rate and leaf area index by 20 to 50%, 7 to 10%, 2 0 to 50% and 20 to 30%, respectively. Root length density (RLD) measur ements showed that in saturated soil, roots of both cultivars were con centrated in the top 0.1 m during the vegetative stage, but in the rep roductive stage, grew down to 0.8 m. Leaf water potential (LWP) was hi gher by 0.3 MPa, and conductances were higher by 5 to 29% in dry than saturated soil. The cultivar TVX1948-012F had greater RLD, conductance and LWP than did with IT82D-889 under saturated conditions. Results s uggest that the medium-maturing cultivar is better adapted than the ea rly-maturing to high rainfall and high water table conditions in the p ost-rice environment. Its shallow rooting under saturated soil conditi ons enables more effective oxygen uptake in the vegetative growth phas e. Deep rooting provides for effective water uptake and increased plan t water status under subsequent drought conditions in the reproductive growth phase.