A null balance method for measuring crop photo-synthesis in an airtight daylit controlled-environment cabinet

Abstract A technique is described for measuring the net canopy photosynthesis of crop stands over periods of 10 min in a near airtight, daylit controlled-environment cabinet. The accuracy of control of the CO 2 , concentration in the cabinet is usually within ±0.5% of the desired value. The amounts of CO 2 used in crop photosynthesis are measured with a linear mass flowmeter accurate to within ±10 mg CO 2 . The total errors incurred in measuring net rates of canopy photosynthesis are estimated to be of the order of 0.75% to ± 2.5%. Records from preliminary trials on tomato in the cabinet are presented as an example of what can be achieved experimentally with the technique.

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