A CLOSED-CHAMBER TECHNIQUE FOR FIELD MEASUREMENT OF GAS-EXCHANGE OF FORAGE CANOPIES

A portable chamber and closed system was used to investigate canopy gas exchange of forage species. The polycarbonate chamber encloses a volume of 62.5 1 from a 50 x 25 cm open base inserted 3 cm into the soil. Air within the chamber is mixed by two 80-mm fans. Evapotranspiration from potted plants measured with the chamber was 25% higher than gravimetric water loss. Nevertheless, chamber values and actual gravimetric water loss were highly correlated. The chamber was tested in a pilot study comparing different forage species at a high-country site in Central Otago. Individual measurements using the canopy chamber were normally completed in less than 2 min, a speed of operation similar to that achieved with conventional leaf chambers. The chamber system provides a simple and useful tool for rapid physiological comparison of whole canopies under field conditions.