A comparison of pressure chamber, leaf-press, and canopy temperature for four species under humid conditions
1990
Sojka, R.E. | Sadler, E.J. | Camp, C.R. | Arnold, F.B.
Numerous techniques are currently available for meassurement of plant water status in field environments, including pressure chambers and indices based upon infrared-determined canopy temperatures. The Campbell-Brewster (J-14) leaf press has been promoted as a compact alternative to the pressure chamber for plant water potential determination. In-depth comparisons of the J-14 (.PSI.J) with the pressure chamber (.PSI.x) or with canopy temperatures (Tc) and crop water stress index (CWSI) have been limited, and an evaluation of the technique in a humid environment was needed. All three J-14 end points [exudation from cut (.PSI.jc) or uncut leaf edges (.PSI.ju) or darkening of interveinal areas (.PSI.jd)] were highly correlated among themselves for the four species studied. Correlations of J-14 end points with other stress indicators from unstable diurnal periods were poor. None of the water status indicators correlated well with leaf diffusive resistance. Our data showed a species-related reliability of the J-14. The J-14 produced r2 values above 0.7 for soybean [Glycine max. (L.) Merr.] for all but comparisons with CWSI or Tc minus air temperature (.DELTA.T), and for corn (Zea mays L.) for .PSI.x only. The J-14 did not perform well for tomato (Lycopersicon exculentum Mill.) or rapeseed (Brassica napus L.), and is probably best regarded only as a relative indication of plant water status in the absence of calibration with other techniques. Failure of .PSI.x or J-14 to correlate well with CWSI underscores difficulty with CWSI measurment under humid conditions.
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