Free-air CO2 enrichment (FACE) using pure CO2 injection:: system description

A free air CO2 enrichment (FACE) system in which rice was grown under elevated CO2 conditions by releasing high pressure, pure CO2 from emission tubes surrounding the crop is described here. Unlike other (FACE) systems, blowers were not used to mix the emitted CO2 with the surrounding air. Four 12-m diameter emission structures ('rings') were constructed. Monitoring and control of CO2 emission was carried out by a series of CO2 and wind sensors, data loggers, controllers and valves. The target CO2 concentration ([CO2]) was 200 mu mol mol(-1) above ambient; enrichment was carried out continuously. Temporal [CO2] control was adequate, with c. 60 and 90% of the air samples at ring center having a [CO2] within 10 and 20% of the target, respectively. Spatial [CO2] distribution was also adequate, with 60% of the ring area having a [CO2] that was within 15% of that at the center. At comparable wind speeds, the pure CO2 injection FACE system described here had a similar performance to that of FACE designs that use blowers to mix the injected CO2 with the air.