Applying Temperature Variation And Relative Humidity Control To Save Energy In Greenhouse Tomato Planting And Endive Propagation

Under the pressure of high price of fossil fuel and globally increasing requirement toreduce CO2emissions, energy saving is playing a vital role in both greenhouse industry andhorticulture research. One way of reducing energy consumption is temperature variationwhich could maximize the solar energy use so as to lower the heating energy input. Relativehumidity (RH) control could broad the RH range so as to reduce the energy consumed indehumidification. We exemplified the research by tomato, a typical year round planting fruitvegetable, and testified the energy saving effectiveness and the impact to plant growth anddevelopment, yield, quality and incidence of botrytis to2cultivars by applying4treatmentsof the temperature variation or conventional temperature control combined with relativehumidity (RH) control or humidity deficit (HD) control. On the other hand, we choose atypical glasshouse propagation leaf vegetable endive as research object and investigate itstemperature sensitivity period and the feasibility of applying variation temperature controlduring its propagation. In addition,2temperature variation regemes is testified in endivepropagation.Major results are as follows.Compared with the conventional stable temperature and HD control, the temperaturevariation and RH control regeme with thermal screen applied at night has accomplished thetarget of18.27%energy saving, and10.31%for temperature variation with HD control. A2.65%saving has been found when using the RH instead of HD control in conventionalgreenhouse temperature manipulating. There are less compromises to plant growth, fruit yieldand quality thourghout the whole planting season. Temperature variation could increase theearly season yield as well as average fruit weight which are closely related to fruit growth rateunder different temperature control. Cultivar “Elegance” picked by truss obtains a increase of2.31kg/m~2(5.3%) of total yield and1.5kg/m~2(3.6%) of marketable yield.It is inevitable that the incident of botrytis occurs in all treatment. The RH controldelayed the incident date and reduced the accumulated number of plant with botrytis.Temperature variation control accounted for the increase in the incident of botrytis, whichwould be effectively lowered if RH control inhibited. In most cases, the relative humidityunder RH control is higher than that under HD control but within the safe rage (<95%), and RH control regeme could effectively control the plant condensation at morning. Take accountof the result of monitoring the different heights, RH at1.2-1.7m level is relatively high; thesupervision of glasshouse RH should be sampled at this level as well as plant temperature.By weekly reciprocal transfer experiment between warm (17℃) and cold (average10.5℃), temperature sensitivity period of endive as well as the its pattern of growth anddevelopment under different temperature both had been investigated. The meristem changeand flower differentiation had been observed by the stero-microscope and electron scanningmicroscope (SEM). The results proved the temperature variation control is feasible in endivepropagation. Within the temperature range from2℃-17℃, endive all can finish flowerdifferentiation which needs24days in cold and60days in warm and bolting in bothcontrolled warm or cold. There is a significant leap of total leaf number when plant isinducted to bolting and10total visible leaves could be used as an index to determine theinduction phase of endive. Low temperature could hasten endive to finish bolting quicklywhen plant is inducted. The top meristem continuously produce side shoot while the stalkemerged and the first flower could blossom at different location of side shoots or adjoiningwith main stalk. That is different from other composite family plants. On the other hand, theyshare similarities in the meristem flower differentiation procedure.Compared with the conventional temperature control, the warmer temperature variation(average17℃) could obtain10%potential of energy saving by model simulating without nosignificant influence on the fresh weight by the end of weaning, yet the high day temperaturewould promote the leaf extension. There are less differences of harvest shoot weight betweentemperature variation and conventional temperature control. Temperature variation couldlower the bolting percentage at some weeks. The lower temperature variation (heating at10℃night,24℃at day) produces small plants and higher incidence of bolting at early season.Extra one week cold shock after propagation promotes bolting significantly.