VI. WATER CONTROL AND MEASUREMENT - MEASUREMENT OF PLANT WATER STATUS OF GREENHOUSE CROPS WITH PRESSURE BOMB AND β-GAUGE

The use of the pressure bomb as a simple field method to measure plant water potential _plant and of the -gauge as a non-destructive method to record continuously the leaf thickness (to be related to plant water content) is described.

With the pressure bomb the relation of _plant and soil water potential _soil at decreasing soil moisture content was determined and the daily course of _plant at constant _soil on sunny days on plants in pots of bean, carnation, chrysanthemum, pepper, spinach and strawberry. With a pressure bomb and with a -gauge plant water status was followed in a crop of roses in a greenhouse with fan and pad cooling. The pressure bomb turned out to be a useful method to assess the level and variations of the plant water balance for most species studied, however, not for all. In the rose crop it indicated variations of the water balance rather sensitively, but the magnitude of _plant was probably measured too low. The -gauge was sensitive enough to measure the effects of short period variations of radiation on the plant water balance.