| 其他摘要 | Water is an important environmental factor restricting the growth of the crops, which has an important impact on the yield and quality of crops. Irrigation is the only source of water supply for greenhouse crops. Moisture deficit will not only reduce the crop’s quality, but also profoundly influence the crop’s yield. Because of this, it is significant to study soil moisture in the greenhouse. Although there are various methods to diagose the soil moisture, the indicators reflecting the change of soil moisture are rare, which are determined by the change of crop itself. In order to improve the diagnosis of the efficiency of crops’ water requirement, the whole of the tomato’s growth period is divided into three parts: seeding, flowing p and fruiting period, and the upper and lower limits of water requirement are also determined during each period. Besides, we also study the relationship among the canopy leaf temperature and soil moisture and the environmental factors in the growth period of the tomato. According to the relationship between canopy leaf-air temperature difference and soil volumetric water content, tomato’s critical canopy leaf tempetature is determined. Furtherly, through studying the relationship between soil volumetric water content and canopy leaf-air temperature difference, the main absorbent area of tomatoes’ root is determined, and supply a scientific basis for diagnosis of farmland soil moisture. The result shows that:
1）The change of canopy leaf temperature is mainly regulated by transpiration. The tomatoes’ transpiration is adjusted by the environmental factors which has a certain impact on canopy temperature. This experiment studied the relationship among temperature, light intensity, humidity and canopy leaf temperature. It shows that the temperature have the greatest effect on the canopy leaf temperature in the greenhouse, which is followed by the light intensity, and the minimum effect is humidity. Therefore, it can be identified that the temperature is the main environmental factors which affect the canopy leaf temperature. 2）By analyzed the diurnal variation of the canopy leaf temperature in the different growth stages of the tomato, it can get: the canopy temperature change consistently with the temperature, which is parabolic structure, and the canopy leaf temperature is lower than the temperature change in the same period, the canopy leaf temperature and temperature reached the maximum value during 13:00-15:00 for the leaf evapotranspiration being the strongest at this time, the contradiction between supply and demand on the crop water requirement and soil moisture is most prominent, which very easily lead to water shortage of tomatoes. Thus this paper mainly observed the canopy leaf temperature and temperature’s change at 14:00 each day in order to analyze the water supply and demand of the plant. 3）In sunlight green house conditions, there were some peaks in the diurnal curve of canopy leaf-air temperature difference from tomato’s seeding stage to fruiting period, and the maxmum of canopy leaf-air temperature difference’s value appear during 13:00-15:00 each day. Accoding to the data at 13:00-15:00 which in tomato’s main growth period, We can get a result which is the △T has a negative relationship with water content（SW）, with the increase of soil moisture, canopy leaf-air temperature difference reduced, on the contrary, the canopy leaf-air temperature difference increased. The related equation is SW=-0.015△T+0.127，correlation coefficient R2 is 0.778, After validated with the measured data, it was found that the measured SW (Y)was well correlated with the simulated one(X), the related equation is Y=0.016+0.941X，and the correlation coefficient R2 is 0.723. Therefore, we could get scientific basis for diagnosis of farmland soil moisture from the water status data which was monitored from canopy leaf-air temperature difference at 13:00-15:00.
4）Threshold of the canopy leaf –air temperature difference refers to the critical value of the canopy leaf –air temperature difference. The value has a great significance for the diagnosis of the critical value of the crop water. This paper has analyzed threshold of the canopy leaf –air temperature difference during the tomato’s fruiting period, and also has done a simple research on the tomato’s seeding and flowering period. The results show that there is a good linear negative correlation between canopy leaf –air temperature difference (△T )and soil water content (SW), and the equation is: SW=-0.014△T +0.130. It can be determined that the maximum of the threshold of the canopy leaf –air temperature difference is -1.5 according to the equation combined the critical soil moisture content which is the minimum of water content in the fruiting period (65% of the field capacity). That is, the plant will be in the state of water shortage when the △T is greater than or equal to -1.5. It can similarly defined that the threshold of the canopy leaf –air temperature difference of tomato’s seeding and flowering. 5）The growth of root has an important role in the crop’s water and nutrients absorb, Its growth and the distribution play an important role in water use and yield. The result showed that the canopy leaf-air temperature difference (△T) was negatively correlated to the difference depths of the soil volumetric water content（SW）, At the same time, there has been the most significantly linear negative correlation in the range of 20-30cm depth, and the correlation coefficient is -0.808. By regression analysis, the equation is SW=-0.017△T+0.155. Thus, it also could be concluded that active zoon of tomatoes’ root is mainly distributed in the range of 20-30cm depth. Key words: tomato; meteorological factor; canopy leaf-air temperature; soil volumetric moisture content; root zone |
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