Abstract
We point out a new composite environmental effect which appears in the neighborhood of limiting values of specific environmental factors for growth. This effect implies the existence of the physiological limitation, and thus the saturation relation of growth against the total effect of environments. Then, there must exist the law of diminishing utility near the extreme values of the latter. It is never preferable that environmental control is carried out in the region of diminishing utility of expensive factors.
Based on this law, we propose the general optimization principle for plant factories which claims that environmental factor with larger cost-performance should have priority of optimization. This principle when applied is expected to improve the payability of totally controlled factories in particular.
