Indicaters And Methods In Monitoring Tomato Water Content Based On Stem Diameter Variation

The methods in monitoring crop water content based on stem diameter variation had a lot of advantages such as convenient,non-destructive,continuous and so on, which attracted more and more experts to research and use it in precise irrigation. Thus, this research would improve the monitoring technology of crop water content as well as the modernization of agriculture water management.The objective of this dissertation is to investigate the characteristics of stem diameter variation of tomato in greenhouse during its different growth stages and the influences of external environment on it, so that proper stem variation indexes used to guide irrigation are determined. Through tomato planted in barrels and plots in greenhouse, the experiment was carried out by randomized blocks design. The irrigation way was drip irrigation during experimental time, and the control of soil water content was mainly by oven drying method as well as assistance of TDR. In addition, the data of meteorological factors during experiment was recorded by automatic meteorological station fixed in greenhouse. The main research results were as follows:(1)The law of tomato stem diameter variation and its relationship with soil water content. Through research of stem variation indexes during different living stages, DI was the main index of diagnosing tomato water content during seedling stage, and MDS could reflect tomato and soil water content more accurately than DI during mid and back living stages. The relationship between MDS and the ratio of losted soil water was polynomial of degree 3. In addition, the stem variation method of guiding irrigation should be used on suny day, and there was no significant difference of stem shrinkage made by different soil water contents on cloudy day. Furthermore, the influence of transpiration to upper stem location is bigger than lower stem location, which means the upper stem shrinkage is bigger than the lower stem shrinkage.(2)The relationships between stem diameter variation indexes and physiology indexes. Through tests of physiology indexes under different soil water contents during tomato mid and back living stages, the daily average values of transpiration rate and stomatal conductance got bigger along with the increase of soil water content, but the daily average values of photosynthetic rate didn't share the same law, and its highest values occurred at 70% relative soil water content usually. In addition, transpiration rate and photosynthetic rate were regulated by stomatal conductance obviously, and there were critical stomatal conductance values below which stem diameter would recover its size during tomato different living stages. There was positive relationship between MDS and sap flow, but the correlation would get weaker along with the increase of soil water content. Furthermore,The daily stem variation of tomato lagged its daily variation of leaf water potential and leaf relative water content, but they had better relationships.(3)The relationships between stem diameter variation indexes and micro meteorological factors in greenhouse. Through comparison and analysis of research results, the change of MDS had the same trend with the change of R(Radiation), and there were positive relationships between MDS and R, VPD(Vapour Pressure Deficit), T(air Temperature), and E(water Evaporation) respectively and negative one with RH(Relative Humidity), and their correlations with MDS got better along with the decrease of soil water content. Through statistical analysis, the estimation model of MDS containing R, VPD and RH was summarized under definite soil water content, and the precision of this estimation model got better along with the decrease of soil water content too.(4)The research of using stem diameter variation method to implement precise irrigation. Through research of tomato stem AMDS(Average values of MDS), the AMDS of 4 tomato stems which share the same configuration and physiological stage had the character of low CV(Variable Coefficient), which can improved the representative ability of sample at one place. Then, the RMDS(Relative MDS) can eliminated the influence of meteorological factors on observation values. In the end, one design of automatic irrigation system based on stem variation was planed, with its hardwares , softwares and topology graph.There were two innovative achievements in this dissertation. Firstly, a new stem diameter index of RMDS was raised which could eliminate the influence of meteorological factors on observation values. Secondly, a new automatic irrigation system based on stem diameter variation was devised, with its hardwares , softwares and topology graph.