| Currently water management of crop in greenhouse is extensive, easily lead to water deficit, excessive irrigation and other issues. Cucumber is the most common greenhouse crop, and it’s much sensitive to soil moisture. To explore crop transpiration law in greenhouse under specific circumstances, optimize irrigation management and provide a theoretical basis for the study of greenhouse automation irrigation and water-saving agriculture, In this experiment, taking cucumber variety "Jinyou 35" for the test material, using pot, setting four soil moisture treatments of sufficient water, mild water stress, moderate stress and severe deficit and combining with the meteorological environment data monitored(such as photosynthetically active radiation PAR,air temperature Ta,relative humidity RH), it studies the transpiration rate and the pattern of leaf water physiological changes of greenhouse cucumber under different soil moisture conditions. It also analyzes the energy balance and water transfer during cucumber transpiration. Finally, study in the view of the meteorology, biology and soil moisture based on crop coefficient and build a transpiration model of greenhouse cucumber nutrition growth.1.Study of greenhouse cucumber water physiology based on leaf scale: In this experiment, it studies cucumber leaves’ diurnal variation of water physiological indicators under different soil moisture treatments, shading treatment and air humidification. The results are as follows: leaf transpiration rate and diurnal variation of stomata conductance all showed a trend of "first increase- then reduce"; leaf water potential and diurnal variation of the leaf water content had a performance of "first reduce- and then increased"; the diurnal variation of leaf- air temperature difference showed " lower- increase- decrease", and it decreased to the minimum between 10 a.m. and 12 a.m., increased to the maximum between 14: 00 and 16: 00. With the severity of shade, the leaf transpiration rate decreased significantly, while the leaf water potential was significantly increased. Leaf- air temperature difference was significantly higher than the normal air humidity treatment under air humidification process, while the moisture content of leaves was increased compared to normal air.Multiple linear regression equation under the influence of relative soil water content and meteorological factors was established in this paper. The results showed that: soil moisture factor, meteorological factor and Water Physiology of cucumber leaves showed a significant correlation. In the mild shading treatment, the impact of cucumber leaf transpiration rate affected by meteorological factors was higher than in the normal light; in severe blackout treatment and air humidification process conditions, soil moisture and meteorological factors had a lower impact on water physiology of cucumber leaves. Analysis of effects of various environmental factors on different physiological indices showed that the main factors affecting leaf transpiration rate, leaf water potential, leaf water content and leaf-air temperature difference were RH, Ta, Rn, Ta.2.Study of greenhouse cucumber transpiration based on individual level: The cucumber transpiration every hour reduced with the shade aggravation and the transpiration in the air humidification were significantly lower compared with in the normal air humidity. Cucumber transpiration in each treatment followed the rule in general: adequate supplies W1> mild deficit W2> severe deficit W3> moderate deficit W4. Analysis of effect of soil moisture and meteorological factors on the cucumber transpiration every hour showed that: soil moisture and meteorological factors had a small effect on cucumber transpiration every hour under the severe shading treatment; while in the rest treatment of light and air humidification, there was an extremely significant correlation between cucumber transpiration every hour and the meteorological factors, soil moisture.The relative soil water content was the most important factor influencing cucumber transpiration each hour.3.Crop transpiration is often estimated by the product of crop coefficient and reference evaportranspiration. However the crop coefficient from related studies vary partly with different environment.In order to reveal the relationship between the demand and supply of potted cucumber’s transpiration in greenhouse, establish transpiration model of greenhouse cucumber, we studied the effects of leaf area index, soil moisture and the meteorological environment on crop coefficient of cucumber by using the replenishment method. A common method for predicting transpiration is the Crop coefficient approach, which affected by Leaf area index, meteorological environment and soil moisture.The reference evaportranspiration was estimate by Penman-Monteith method, which aerodynamically drag was calculated by Thom-Oliver method with the wind speed being zero. We made the figure of crop evaportranspiration(ET) and reference evaportranspiration(ET0) that changed daily in two experiments, the result shows that the crop was supply-limited at initial stage because of low leaf area index(LAI),ET was equal to or greater than E0 in the later stage because LAI achieved a sufficiently high value and the crop was not supply-limited. 1)Leaf area index :In this paper, we show that the correction coefficient of leaf area index varies as logistic curve with the increase of leaf area index, and point of inflexion on the curve is LAI=1.46,when LAI increases to 1.46, the influence of leaf area index on the crop coefficient reaches the maximum. 2)Meteorological environment :We selected reference crop evaportranspiration 0E as effecting factor of meteorological environment on crop coefficient. Correction coefficient of meteorological environment increases first and then decreases with E0’s variation, and the critical point is 3.2; when0 E ≤3.2, the correction coefficient of meteorological environment can be described by a logistic curve with the increase of 0E; when0 E >3.2, the correction coefficient of meteorological environment conform to a straight line with a slope of-0.64 with 0E ’s increase. 3)Soil moisture :Relative water content has effects on transpiration of cucumber, that is, the soil critical moisture point 0? is decided by potential transpiration rate of cucumber, when the soil moisture is more than 0?, soil water correction coefficient is 1; when the soil moisture is less than 0?, the transpiration rate is of inhibition. The correction model accurately predicted cucumber transpiration(RMSD< 20% of observation mean) under different water treatment, confirming its simplicity and efficacy. |
PDF Full Text Request