The interaction of cowpea maturity with degree of waterlogging in the post-rice environment
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Cowpea [Vigna unguiculata (L.) Walp] is grown widely as an inexpensive source of protein in tropical regions. Production is often limited by either waterlogged or dry soils in the wet-dry transition period following rice because periodically saturated soils are followed by progressively severe drought. An optimum fit of cultivar phenology to these situations is crucial to higher, stable yields. The responses of a set of diverse cowpea cultivars differing in maturity were compared under a line-source moisture gradient applied during the vegetative stage on an isohyperthermic, clayey, Typic Tropudalf with a fluctuating shallow water table, during two dry seasons in the Philippines. In 1986-87, in saturated soil, the mean yields of the medium-maturing grain (460 kg ha-1) and dual-purpose (460 kg ha-1) types exceeded yield of the early-maturing grain (250 kg ha-1) and vegetable (210 kg ha-1) types, with a similar ranking (920, 730, 470, and 390 kg ha-1) without irrigation. In 1988, the medium-maturing cultivar group had a mean yield 985 kg ha-1 in saturated soil and 1389 kg ha-1 in unirrigated, again exceeding the early-maturity group with yields of 544 and 985 kg ha-1, respectively. Saturated soil reduced seed yields by 10 to 71% in 1986-87 and 10 to 42% in 1988. Pods per plant, seeds per pod, and individual seed mass of the cultivars were reduced 13 to 32%, 12 to 19%, and 3 to 12%, respectively. The results suggest that the best medium-maturing cultivars had superior adaptation to that of the best early-maturing cultivars in a post-rice environment with prolonged high rainfall and a high water table. Contrasting results are expected in post-rice niches with a deep water table and limited soil water reserves.
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