The relation between photosynthesis and environmental factors is presented. Here, we report the results from cotton plants grown in naturally-lit plant growth chambers in which temperature, CO₂, water, and nutrients were controlled and varied systematically. Photosynthesis of crop canopies was measured continuously along with other related vegetative growth parameters and abiotic variables. Photosynthesis is the driving process of dry matter production, but factors affecting vegetative growth and development are important aspects of cotton production. Canopy photosynthesis is not light saturated in Midsouth radiation environments. Present-day cropping practices allow the crop demand for photosynthates to occur during declining solar radiation. Current atmospheric CO₂ levels are limiting cotton production, and rising CO₂ will benefit cotton growth and yield. Temperature has a small effect on canopy photosynthesis and thus primary production is sustained in a wide range of temperatures. Temperature however, strongly influences vegetative growth and development and thus light capture during the vegetative period, and light conversion efficiency during much of the boll-filling period. Temperature above 28°C limits both vegetative growth and more importantly boll retention or sink capacity. Water, nitrogen and potassium deficits decrease leaf growth more than photosynthesis. Thus, crop production is a function of many processes from cellular to canopy levels. Increasing production and yield requires knowledge of processes at all levels.