GROWTH AND YIELD OF COTTON IN RESPONSE TO A FREE-AIR CARBON-DIOXIDE ENRICHMENT (FACE) ENVIRONMENT

To quantify the growth and yield responses to CO2 enrichment in an open field setting, free-air CO2 enrichment (FACE) technology was used to expose a cotton (Gossypium hirustum L.) crop to 550 mumol mol-1 CO2 throughout the growing seasons of 1989, 1990 and 1991 in fields near Maricopa, Arizona. In 1990 and 1991 a water stress treatment was also imposed. Response data for all years were consistent, and the data for 1991 were the least compromised by unusual weather or equipment failures. In that season the biomass was increased 37% by the 48% increase in CO2 concentration. Harvestable yield was increased 43%. The increase in biomass and yield was attributed to increased early leaf area, more profuse flowering and a longer period of fruit retention. The FACE treatment increased water-use efficiency (WUE) to the same amount in the well-irrigated plots as in the water-stressed plots. The increase in WUE was due to the increase in biomass production rather than a reduction of consumptive use.