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 ope n field setting, free-air CO2 enrichment (FACE) technology was used to expose a cotton (Gossypium hirustum L.) crop to 550 mumol mol-1 CO2 t hroughout the growing seasons of 1989, 1990 and 1991 in fields near Ma ricopa, Arizona. In 1990 and 1991 a water stress treatment was also im posed. Response data for all years were consistent, and the data for 1 991 were the least compromised by unusual weather or equipment failure s. 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 tr eatment 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 reduct ion of consumptive use.