This study is designed to determine the estimation methods of water saturation deficit (W. S. D.) as a reliable indicator of water balance in Satsuma orange leaves, and also to determine the effects of soil moisture and fertilizer supply on the W. S. D. and the apparent photosynthetic rate of leaves.
1. The following method could be recommended as a method for simple and accurate determination of W. S. D. of leaves. Leaves is cut out from experimental plants, then put petiols with a whole leaf in a dish containing distilled water for 24 hours for saturation in a moist chamber. Calculation of W. S. D. is as follows:
W. S. D.(%)=Saturated fresh weight-Initial fresh weight/Saturated fresh weight-Oven dry weight×100
This method involves many considerations, namely: leaf age, leaf position on a shoot, and leaf from shoot bearing fruit or not.
2. The soil moisture affects the degrees of W. S. D. in leaves very considerably, the degrees increasing with decreasing soil moistures. The value of W. S. D. at a low moisture level is 2.6 times as high as the value of it at a medium soil moisture level. While an increase in fertilizer supply cause a progressive increase in W. S. D.
3. A reduction in soil moisture and an increase in fertilizer supply results in a decrease in the rate of apparent photosynthesis. When the soil is allow to dry out, as is shown at a low soil moisture level, reduction in the rate of photosynthesis become evident.
There is a highly negative correlation between the W. S. D. and the rate of apparent photosynthesis.