Influence of irrigation and nitrogen on herbage and oil yield of palmarosa (Cymbopogon martinii) under semi-arid tropical conditions

The control of CO2 levels is reported for a Free-Air Carbon dioxide Enrichment (FACE) facility employed in a vineyard at Rapolano, Italy in 1996 and 1997. This control is required for evaluating the validity of a biological experiment conducted on grapevine in CO2 enriched and control experimental plots. Six rectangular emission arrays enclosing seven plants each were installed in the vineyard imposing three CO2 exposure levels (ambient, 550 and 700 mumol mol-1) and monitoring CO2 levels at the centre of each experimental plot. In the 2 years, average seasonal (May¯September) CO2 levels during treatment hours (05:00¯19:00 h) varied from 697 to 698 muumol mol-1 for 700 mumol mol-1 target treatment and from 549 to 550 for 550 mu mol mol1 target treatment. The averaged 1 min measurements of CO2 concentration were within 20% of the target concentrations for more the 80% of the time. The FACE facility also provided a good spatial control of CO2 concentration for an experimental sampling volume of 15.7 m3 (8 m×1.4 m×1.4 m), including five plants per plot.