Research On The Diagnosis Of The Soil Volumetric Water Content During Tomato's Growth Period In Greenhouse

Water is an important environmental factor restricting the growth of the crops, whichhas an important impact on the yield and quality of crops. Irrigation is the only source ofwater 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 soilmoisture in the greenhouse. Although there are various methods to diagose the soilmoisture, the indicators reflecting the change of soil moisture are rare, which aredetermined by the change of crop itself. In order to improve the diagnosis of theefficiency of crops' water requirement, the whole of the tomato's growth period is dividedinto three parts: seeding, flowing p and fruiting period, and the upper and lower limits ofwater requirement are also determined during each period. Besides, we also study therelationship among the canopy leaf temperature and soil moisture and the environmentalfactors in the growth period of the tomato. According to the relationship between canopyleaf-air temperature difference and soil volumetric water content, tomato's critical canopyleaf tempetature is determined. Furtherly, through studying the relationship between soilvolumetric water content and canopy leaf-air temperature difference, the main absorbentarea of tomatoes' root is determined, and supply a scientific basis for diagnosis of farmlandsoil moisture. The result shows that:1)The change of canopy leaf temperature is mainly regulated by transpiration. Thetomatoes' transpiration is adjusted by the environmental factors which has a certain impacton canopy temperature. This experiment studied the relationship among temperature, lightintensity, humidity and canopy leaf temperature. It shows that the temperature have thegreatest 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 thetemperature is the main environmental factors which affect the canopy leaf temperature.2)By analyzed the diurnal variation of the canopy leaf temperature in the differentgrowth stages of the tomato, it can get: the canopy temperature change consistently withthe temperature, which is parabolic structure, and the canopy leaf temperature is lower thanthe temperature change in the same period, the canopy leaf temperature and temperaturereached the maximum value during13:00-15:00for the leaf evapotranspiration being thestrongest at this time, the contradiction between supply and demand on the crop waterrequirement and soil moisture is most prominent, which very easily lead to water shortageof tomatoes. Thus this paper mainly observed the canopy leaf temperature andtemperature's change at14:00each day in order to analyze the water supply and demand ofthe plant.3)In sunlight green house conditions, there were some peaks in the diurnal curve ofcanopy leaf-air temperature difference from tomato's seeding stage to fruiting period, andthe maxmum of canopy leaf-air temperature difference's value appear during13:00-15:00each day. Accoding to the data at13:00-15:00which in tomato's main growth period, Wecan get a result which is the△T has a negative relationship with water content(SW), withthe increase of soil moisture, canopy leaf-air temperature difference reduced, on thecontrary, the canopy leaf-air temperature difference increased. The related equation isSW=-0.015△T+0.127, correlation coefficient R~2is0.778, After validated with themeasured data, it was found that the measured SW (Y)was well correlated with thesimulated one(X), the related equation is Y=0.016+0.941X,and the correlation coefficientR~2is0.723. Therefore, we could get scientific basis for diagnosis of farmland soil moisturefrom the water status data which was monitored from canopy leaf-air temperaturedifference at13:00-15:00.4)Threshold of the canopy leaf–air temperature difference refers to the critical valueof the canopy leaf–air temperature difference. The value has a great significance for thediagnosis of the critical value of the crop water. This paper has analyzed threshold of thecanopy leaf–air temperature difference during the tomato's fruiting period, and also hasdone a simple research on the tomato's seeding and flowering period. The results show thatthere 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 bedetermined that the maximum of the threshold of the canopy leaf–air temperaturedifference is-1.5according to the equation combined the critical soil moisture contentwhich 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 orequal to-1.5. It can similarly defined that the threshold of the canopy leaf–air temperaturedifference of tomato's seeding and flowering.5)The growth of root has an important role in the crop's water and nutrients absorb, Itsgrowth and the distribution play an important role in water use and yield. The resultshowed that the canopy leaf-air temperature difference (△T) was negatively correlated tothe difference depths of the soil volumetric water content(SW), At the same time, therehas been the most significantly linear negative correlation in the range of20-30cm depth,and the correlation coefficient is-0.808. By regression analysis, the equation isSW=-0.017△T+0.155. Thus, it also could be concluded that active zoon of tomatoes' rootis mainly distributed in the range of20-30cm depth.