Simulating And Validating Of Muskmelon Transpiration Model In Greenhouse

This study was conducted with muskmelon “Yipintianxia208” plants as the experimentalmaterial. Soil water gradients were set through pot experiments and artificial watercontrolling. With interval sowing, transpiration experiments were conducted under differentmeteorological environment and soil water content. The objective was to explore therelationship between daily muskmelon transpiration and crop physiology parameters、meteorological environment、soil moisture parameters, reveal the transpiration impact factorsand their influencing mechanism and establish the model of transpiration for greenhousemuskmelon with biological and physical mechanism.This study can provide a theoretical basefor water optimization management and effective utilization of water resource for greenhousemuskmelon. The main results were as follows:1. Establishing the evaluation system of influencing factors of muskmelon transpirationin greenhouse and revealing the mechanism of interaction effect.The impact factors of daily transpiration of muskmelon in greenhouse were analysed byPearson correlation analysis and path analysis. The daily transpiration of muskmelon ingreenhouse had high significant positive correlation at the0.01level with impact factorsexcept daily average relative humidity were significant negative correlation at the0.01level.The leaf area index had maximum positive correlation coefficient between daily transpirationof muskmelon, the following were relative soil water content, daily average temperature anddaily solar radiation accumulation sequently. The leaf area index had maximum direct impacton daily transpiration of muskmelon, the following were daily average temperature while therelative soil water content、daily solar radiation accumulation、daily average relative humidityhad little direct impact. The leaf area index was the junction combining soil moisture、meteorological environmental factors to muskmelon transpiration. Soil moisture had indirectpositive function on transpiration through promoting leaf area index. Daily average relativehumidity had indirect negative function on transpiration through inhibiting daily averagetemperature. Daily solar radiation accumulation had indirect positive function on transpirationthrough promoting leaf area index and daily average temperature.The influence size order of decision coefficient of influencing factors of muskmelontranspiration was：Leaf area index> daily average temperature> daily solar radiation accumulation> daily average relative humidity> soil water content.Therefore, Leaf areaindex was decision variable for its greatest comprehensive effect on transpiration；relative soilwater content was rate-limiting variable, although it had small direct effect but made indirectgreat influence on transpiration through other factors such as leaf area index. The decisioncoefficient of surplus factors was22.13%, indicating that some factors making significantlyimpact on transpiration had not been taken into account.2. Developing the predicating model of transpiration for greenhouse muskmelon.Establishing dynamic changing model of the accumulative transpiration of muskmelon inthe whole growth period.The results show that the accumulative transpiration ofmuskmelon presented “slow—quick—slow” dynamic trends, feasible for the logisticfunction to simulate with the independent variable of days (t) after transplanting and dividegrowth stage. The days (t) after transplanting to=39.1、t1=26.7、t2=51.5were the threefeature points of the logistic model calculated from zero point of the second and thirdderivative, dividing whole growth period into four subinterval of initial period、growth period、mature period and degenerating period.The coefficient of determination was0.997, givingsatisfactory prediction of the dynamic change of the accumulative transpiration.Establishing the predicating model of daily transpiration of muskmelon in vegetativegrowth period in greenhouse.The greenhouse environmental sub-model suitable forcalculating the reference crop evapotranspiration in greenhouse was deduced by modifyingthe item of aerodynamics of Penman-Monteith equation according to the specific environmentin greenhouse; The crop factor sub-model was established with the independent variable ofleaf area index, the form of model was linear function;The soil moisture sub-model wasestablished with the independent variable of soil relative effective moisture content, the formof model was logarithmic function. With interval sowing, model parameters were estimatedaccording to measurement data of different sowing dates in a year. Prediction accuracy ofmodel for sufficient irrigation and water-saving irrigation was verified according tomeasurement data when the relative soil water content was80%、70%、60%, the mean relativeerror was11.46%、18.24%、17.85%respectively. The model was the beneficial exploration forthe application of Penman-Monteith equation under greenhouse environment andwater-saving irrigation which had a good application foreground and popularized value.