Summary A free air CO 2 enrichment (FACE) system in which rice was grown under elevated CO 2 conditions by releasing high pressure, pure CO 2 from emission tubes surrounding the crop is described here. Unlike other (FACE) systems, blowers were not used to mix the emitted CO 2 with the surrounding air. Four 12‐m diameter emission structures (‘rings’) were constructed. Monitoring and control of CO 2 emission was carried out by a series of CO 2 and wind sensors, data loggers, controllers and valves. The target CO 2 concentration ([CO 2 ]) was 200 µmol mol −1 above ambient; enrichment was carried out continuously. Temporal [CO 2 ] control was adequate, with c . 60 and 90% of the air samples at ring center having a [CO 2 ] within 10 and 20% of the target, respectively. Spatial [CO 2 ] distribution was also adequate, with 60% of the ring area having a [CO 2 ] that was within 15% of that at the center. At comparable wind speeds, the pure CO 2 injection FACE system described here had a similar performance to that of FACE designs that use blowers to mix the injected CO 2 with the air.
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