STEM DIAMETER MEASUREMENT AND ITS RELATIONSHIP TO WATER STATUS IN COTTON.

Abstract

Plants under variable water stress exhibit a contraction of their stem diameter. This variation can be monitored to determine the plant water status which, in turn, will lead us to a method of scheduling subsequent irrigation. In this dissertation, the possibility of determining the water status in cotton plants by automatically sensing their stem diameter variation was explored. A full description of the displacement sensor, the electronic circuits used for automatic stem diameter monitoring and the data analysis is given. Simultaneous measurement of the leaf water potential and the stem diameter variation were done for a total of eight days during an irrigation cycle. Statistical analysis was performed to infer the water status in the plant from the stem diameter variation. It was discovered that the stem diameter variation lags the water potential by two hours, and that there was no simple linear correlation between them. In fact, it was discovered that the stem diameter variation was not only a function of the leaf water potential of the plant as it was believed; but indeed, it is also a function of the soil water condition. According to the results obtained, a basic model to describe the relationship between the stem diameter variation and the plant and soil water condition was developed.