Improvements in yield should involve genetic changes that reduce yield-limiting resources. In Virginia, the primary yield-limiting resources are water, light, nutrients, carbon dioxide and oxygen. Water is the most likely limiting factor due to the low water-holding capacity of Virginia's soils. The ability of one variety to more effectively acquire water in relationship to other varieties could result in greater yields under water-stressed environments.

This study will determine the magnitude of change in irrigated and dryland soybean yield with variety improvement in full-season and double-cropped soybean systems; and to determine the physiological mechanisms contributing to yield...