Most of the authors knowledge concerning the effects of ultraviolet-B(UV-B) radiation was obtained with artificial UV radiation sources supplementing either artificial white light in growth chambers, or solar radiation in greenhouses and in the field. However, these artificial sources do not precisely match the solar spectrum. Few studies have documented the effects of UV-B on total plant yield under field conditions. One notable exception is a six-year field study with soybean demonstrating harvestable yield reductions under a simulated 25% ozone depletion. These effects are further modified by prevailing microclimatic conditions. Plants tend to be less sensitive to UV-B radiation under drought or mineral deficiency, while sensitivity increases under low levels of visible light. Further studies are needed to understand the mechanisms of UV-B effects and the interactions with present stresses and future projected changes in the environment.