Crops fail to achieve their genetic potential, even under the best crop husbandry, because of environmental constraints. Improvements in crop adaptation to environmental stresses can be better undertood if the decrease in potential by each environmental factor is assessed. The objective of this reserach was to describe the concept of environmental productivity index and its efficiency in quantifying stress effects on crop growth. Experiments were conducted in the sunlit Soil-Plant-Atmosphere-Research facility using cotton as a model crop. Temperature, atmospheric CO2, water, ultraviolet-B radiation and nutrients were controlled and varied systematically. Cotton canopy photosynthesis was measured along with vegetative and reproductive growth parameters and abiotic variables. Potential growth, development and photosynthesis, defined, as the rate/amount of an individual process occurring under optimum environmental conditions was decreased to develop stress-specific reduction factors or indices limiting crop growth. Even though photosynthesis is the driving process of dry matter production, effects of environmental factors on vegetative and reproductive growth have important impacts on cotton production. All indices ranged from zero, when a given environmental stress was totally limiting a process, to one, when it did not limit that process. The indices represent the fractional limitation due to the environmental stress. These environmental productivity indices were quantified, modeled and incorporated into a mechanistic cotton model, and validated under field conditions.