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Water Use by Monocropped and Intercropped Cowpea and Sorghum Grown after Rice

Dep. of Soil Sci., Oregon State Univ., Corvallis, OR 97331

A. N. Villegas, A. Polthanee and H. S. Centeno

Multiple Cropping Dep., Int. Rice Res. Inst., P.O. Box 933, Manila, Philippines

^* Corresponding author.

Water remaining in the soil after flooded rice (Oryza sativa L.) is a major source for crops grown during the dry season. To develop improved management systems, quantitative information describing water extraction from previously puddled and flooded fields is needed. Water used by monocropped and intercropped cowpea [Vigna unguiculata (L.) Walp.] and sorghum [Sorghum bicolor (L.) Moench] treatments grown on a fine, mixed, nonacid isohyperthermic Andaqueptic Haplaquoll after harvesting flooded rice was compared to water lost from a fallow treatment. Determinations were to 1.1 m. Water used before cowpea harvest was similar within a treatment among years, but among treatments monocropped cowpea used 172 mm, monocropped sorghum 135 mm, the intercrop 162 mm, and fallow 121 mm. Water used between cowpea and sorghum harvests ranged from 22 to 118 mm, varying with rainfall after cowpea harvest. Species were compared by expressing grain yields in Mg glucose hectare^–1 required to synthesize grain. Glucose equivalent yields from monocropped cowpea ranged from 1.90 to 1.98 Mg glucose ha^–1, monocropped sorghum from 1.99 to 3.66 Mg glucose ha^–1, and the intercrop from 1.99 to 4.36 Mg glucose ha^–1. Mean water use efficiency by monocropped cowpea, monocropped sorghum, and the intercrop was 11.3, 12.4, and 16.5 kg glucose ha^–1 mm^–1. Monocropped cowpea and the cowpea-sorghum intercrop each use about 50% more water than is lost from fallow. Whereas the cowpea monocrop and the intercrop use about the same quantities of water when grown during the dry season after rice, the intercrop will use water more efficiently but yields from it will not be as stable as those from monocropped cowpea.

Received for publication November 21, 1988.