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Dependence of Dioscorea Tuber Growth Rate on Water Content of an Andept Soil¹

ABSTRACT

Unexpectedly low tuber yields of a pharmaceutical crop (Dioscorea species) on an Andept soil in Central America led to a study of soil-related limitations. Readily available water (0 to –20 cbar) controlled tuber growth rates to a far greater extent than other environmental factors. Relative tuber growth rates of seedlings increased linearly as soil water content increased from 0.14 to 0.45 cm³ cm^–3. Growth increases occurred with water contents above field capacity provided that soil porosity was not reduced by compaction. Most efficient tuber dry solids accumulation occured at the mid-range of soil water contents employed and amounted to about 2.0g liter ^–1 of water consumed by the plant. Total plant (tuber, vine, and roots) water use efficiency was 6.2 g liter ^–1 at the same soil water content.

Water use efficiency in general was related to soil water content in a bifunctional manner, whereas stomatal activity as measured by leaf diffusive resistance increased continuously with increase in soil water content. Thus, highest rates of deposition of photosynthate in the tubers were accomplished by highest but least efficient rates of water consumption.

The results indicate that low bulk density, free-draining Andept soils limit Dioscorea tuber growth rate by an inability to deliver without interruption the required volumes of lowtension water.

¹ Contribution from the former research staff of Finca Buena Vista in Central America. Project Coordinator, Ray F. Dawson, 40 Palmer Ave., Winter Park, FL 32789. The work was supported by the Upjohn Company.

² Plant physiologist, Horticulturist, and Agricultural Engineer, respectively. The senior author is Emeritus Professor of Plant Biology and former Director of International Agricultural Programs in Rutgers Univ. and the New Jersey Agric. Exp. Stn. The second author is now manager of an experimental farm for the Asgrow Seed Co., San Juan Bautista, Calif.; and the third author is a graduate student in the Dep. of Agric. & Chemical Engineering in Colorado State Univ.

Received for publication March 28, 1980. Accepted for publication June 24, 1980.