Cowpea Water Relations and Growth Response on a Toposequence Water Table Gradient
- J. Timsina,
- D. P. Garrity and
- R. K. Pandey
- I nst. of Agric. and Animal Sci., Tribhuvan Univ., P.O. Box 984, Kathmandu, Nepal
S outheast Asian Regional Research Program, Forest Research and Developement Centre, Jalan Gunung Batu no. 5, P.O. Box 382, Bogor 16001, Indonesia
C ropping Systems Res., Indian Council of Agric. Res., Modipuram 250 110, Meerut, U.P., India
Cowpea sown after wetland rice in tropical monsoon climates is frequently subjected to soil saturation and a high water table during early growth. We compared the effects of variation in water table regime on the shoot and root growth, and plant water relations of two medium-maturing (cv. TVX3236-01G and TVX3410-02J) and two early maturing (cv. BS6 and IT82D-889) cowpea [Vigna unquiculata (L.) Walp] cultivars in three water table depth regimes on a Typic Tropudalf toposequence. Our objective was to elucidate the possible mechanisms of differential cultivar adaptation to shallow water table conditions. The shallow water table regime (SWT) significantly reduced the total dry matter accumulation and harvest index for BS6, an early maturing cultivar (reductions in stems, leaves, pods, and total dry matter by 82, 77, 88, and 84% respectively), while the least reductions (reductions by 44, 3, 57 and 55%, respectively) was observed for TVX 3410-02J, a medium-maturing cultivar. Roots of the medium cultivars were more concentrated in the top 0.2m in the SWT Site than those of the early-maturing cultivars. Roots of the medium cultivars later penetrated to 0.8-m maximum depth compared to 0.6-m maximum depth for the early cultivars, and extracted soil water from 20 cm deeper in the soil profile than the early maturing cultivars. The medium-maturity cultivars maintained higher leaf water potentials and lower canopy temperatures throughout the season. This was associated with greater end-of-season total soil profile water extraction. The medium-maturing cultivars showed better adaptation to shallow water table conditions due to superior plant water status, rooting pattern, and biomass production and partitioning.
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