[Rice-wheat rotational FACE platform. I. System structure and control].

A Free Air CO2 Enrichment (FACE) system for rice and winter wheat rotation was established, elevated CO2 concentration was controlled to 200 mumol.mol-1 above ambient by computer system platform according to ambient CO2 concentration variation, wind direction, wind speed, canopy height and day-night changing. Experiments showed that the main factors affecting control precision are wind speed, crop and soil respiration and thickness of diffuse layer. After parameters adjustment, in daytime the time fraction for control precision achieve 80% is 83%, in night is 68%. The CO2 concentrations distribution in FACE rings are uniformity. The set CO2 is 557 mol.mol-1 in daytime and 608 mol.mol-1 in night. In 2001 rice season the target achievement ratios (TAR) were 1.03 after sunrise and 1.09 after sunset, respectively.