Dependence of Dioscorea Tuber Growth Rate on Water Content of an Andept Soil
1980
Dawson, Ray F. | Shrum, Jeffrey E. | Mohammed, Robert A.
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.
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