Transpiration of Soybeans as Related to Leaf Area, Root Length, and Soil Water Content
1979
Eavis, B. W. | Taylor, H. M.
Soybeans [Glycine max (L.) Merr. ‘Corsoy’] were grown in 100 or 162 liter containers located in a field environment near Ames, Iowa, in order to determine the effects on transpiration rates and leaf water potentials of varying the root length (RL) to leaf area (LA) ratios during a water extraction cycle. The RL/LA ratios were varied by combining two fertility levels with two watering history treatments using Clarion clay loam topsoil (Typic Hapludoll). Two container sizes provided two different quantities of water storage at the start of the drying cycle. The containers were sealed around the plant stems to prevent evaporation during the drying cycle. Transpiration rates were determined from differences in total container weights at known times. Leaf areas were estimated on several days from length-width measurements on all terminal leaflets of a plant. Leaf water potentials were estimated by the pressure chamber technique. Root lengths were determined at harvest. Total transpiration (cm³/day) from the container increased linearly with leaf area. Transpiration rate (cm³/cm²/day) decreased linearly as soil water content deceasedbut at any particular soil water content, root length had no significant (P = 0.95) effect on transpiration rate. When a particular treatment increased the RL/LA ratio, water uptake rate per m of root decreased proportionately. This inverse relationship between total root length on the plant and uptake rate per m of roots enabled the plants to maintain equal leaf water potentials (regardless of the RL/LA ratios) when the roots were located in soils of equal water contents.
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