The Study On Measurement Of Stem Water Content Based On Standing Wave Theory

At present, the study on the plant water transmission and plant water balance have a same technology bottleneck which is refer to lack of convenient non-destructive exact and low-cost plant water content measuring instrument. Because of the same reason, the precision irrigation technology based on plant water requirement as the development trend of water-saving irrigating technology is limited. At abroad, they could get exact plant water content by TDR (Time Domain Reflectometry) which is used to measure soil water content. But there are not special sensors for measuring plant water content in china. Because of the complicated technology and high price of TDR, it is difficult to popularize. Therefore, the author try to utilize standing wave ratio of the microwave transmission line theory to measure plant water content in this paper.This paper illustrates the principle of measuring medium dielectric constant with standing wave, and proves the feasibility of measuring plant water content with it. The author developed a plant- moisture-sensor, and optimized its probe construction and transmission line characteristic impedance, then calibrated the sensor with oven dry method. The results of a series of experiment indicate that the sensor can offer wide measuring range high degree of accuracy and good linear output for measuring plant water content. The successful study filled up the blank of plant water content measuring- technique.