Afternoon Water Deficits and Grain Yields in Old and New Soybean Cultivars
1980
Boyer, J. S. | Johnson, R. R. | Saupe, S. G.
Plant water deficits affect many metabolic processes, and soybean (Glycine max L. Merr.) is subject to water deficits during midday even when soil water is adequate under field conditions. Our objective was to determine if yield improvement by plant breeding has been associated with avoidance of these deficits in soybean. A 3- year experiment was conducted on highly productive soils in central Illinois with two soybean maturity groups each represented by four cultivars. The cultivars had been released between 1911 and 1968 in the USA. Soil water availability was high in all 3 years. However, leaf water potentials were frequently below −11 bars at midday, which we defined as a water deficit. Cultivars with low yields experienced larger water deficits than those with high yields. The largest water deficits were found in the oldest cultivars and were present in all the fully illuminated leaves of the canopy. The deficits were large enough to be potentially mhibitory to afternoon photosynthesis and other metabolic processes. Considerable yield improvement was apparent in the newer cultivars of both maturity groups when their yields were compared with those of older cultivars in the common environment represented by this experiment. Rooting densities of two cultivars showing extremes of midday water deficits indicated that the cultivar with the least water deficit (‘Wayne’) had a greater root density than the cultivar with the largest deficit (’Richland’). The data suggest that old cultivars experience yield inhibiting water deficits at midday in central Illinois in soil containing adequate water. Breeding soybean for high yield has, at the same time, selected for superior shoot water status in midday, perhaps as a result of increased root densities.
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