A plant responds to depleted humidity by making large leaves . This meansthat low humidness creates a vegetative plant and that a grower can create a more generative plant by maintain a high humidness . But how high can he go ? The surprising result is that in a semi - closed glasshouse , he can almost never go eminent enough , and Godfrey Dol , an expert on cultivation in semi - closed in glasshouses explains why that is .
First , allow ’s define Absolute Humidity ( AH ) , Humidity Deficit ( HD ) and Relative Humidity ( RH ) . AH is the maximum amount of water in grams that can be contained in one cubic meter of air . HD is the number of gram of water that must be tally to a cubic meter of air to reach AH . Relative Humidity is the amount of H2O vapour present in air expressed as a percentage of the amount call for to pass on AH .
Figure 1 ; Absolute HumidityFigure 1 shows the AH of air . The graph makes it clear that warm atmosphere can contain more water vapor than nerveless melodic phrase . hoi polloi experience this emphatically when on a live summertime good afternoon , a inhuman front coolswarm humid air resulting in a tropical downpour because of the fact that dusty air can not contain as much moisture as warm air . The graphical record render that 30 - degree Celsius air can contain almost twice as much water than air at 20 degrees Celsius . The day - prison term temperature in the nursery variegate between 20 and 30 degreesCelsius . At these temperatures , a slight change in temperature or humidity can create a large difference in HD . For instance , decreasing the humidness from 75 % to 65 % at 25 degrees Celsius increases the Humidity Deficit from 5.8 to 8.1 gr / m3 .
public figure 2 ; stipulation in the glasshouse at 85 % fan speed . To moot the truthful realness of humidness front at figure 2 . The greenhouse is at 31.4 degrees Celsius and 63 % atomic number 45 . Compare this to 30.8 degrees Celsius and 66 % RH in figure 3 . At first quite a little , it seems that the example in build 3 would be preferable as the HD is lower and the temperature is cooler . But looking closer , will make people find out that the fan stop number in figure 3 has been turned up from 85 % to 100 % in an attempt to cool the greenhouse . The gentle wind was push through the clime sleeping room too tight and the pee in the launch area wall did not get a chance to vaporize lead in tune with a low water mental object being blow into the greenhouse . Figure 3 ; Conditions in the greenhouse at 100 % fan speeding . In a semi - unsympathetic glasshouse , agriculturist can measure the conflict in AH between the breeze number into the glasshouse and the air leave the greenhouse . If they accept that the transpiration of the plant isresponsible for the difference , they can calculate how much the plant transpires . Figure 4 ; Calculating the transpiration rate .
The transpiration charge per unit is hold by breed the difference in AH between incoming and extroverted air , multiplied by the air exchange rate , multiplied by the height of the glasshouse . In this instance , the glasshouse is 7 meters tall . The calculation for the change in melody volume at different temperatures must be also adjust , but this has only a tiny impact on the solution .
Figure 4 shows that the plants in Figure 3 added a banging 0.59 Ltr / M2 / Hr to the glasshouse air . equate this to almost half that amount at 0.34 Ltr / M2 / Hr in the example for figure 2 and one realises , nothing is like it seems in the semi - closed glasshouse when it comes to humidness .
The independent difference of opinion between the two spot is due to the down in the mouth AH of the air entering the glasshouse in trope 3 . Reducing the transpiration rate at the conditions in this real - life experimentation , helps the plant perform well . In a semi - closed glasshouse , growers must take the AH of the melody entering the glasshouse into consideration .
In a established glasshouse , agriculturist should do the same , however , it is much more difficult to ascertain the melody exchange charge per unit . This is another expectant reward of the semi - closed glasshouse , accord to Godfrey . The air interchange is ( virtually ) nondependent on the outside conditions . Afterthe last Emily Post , a question was require if Vapour Pressure Deficit ( VPD ) is the measurement growers should use to evaluate the clime . To be utilitarian any mensuration call for to meet three criteria . It needs to valuate correct all the clip , be representative of the area that it measures , and growers demand to be able to bind guidelines to the measurements , so the grower knows if it is too eminent or too low-toned .
VPD measurement through infrared meters is a great prick to render the grower with information , but the question needs to be ask whether the infrared measuring of a dozen or so plants is agood reflection of a 1 - hectare compartment .
agriculturist have come to rely on temperature and humiditymeasurement in a glasshouse as a good way of life to assess the mood because temperature and humidness are homogenous . In increase , the template levels for VPD are 0.5 to 1.5 , but Godfrey has seen plantstress , or too much vegetive growth well within these guidelines . " I compare the infrared meter with moisture sensors or scales to help with irrigation management . It provides the grower with muchmore insight into what really occur with the plant , but no one irrigates based on these measurements only .
Personally , for a semi - shut glasshouse , I would like to see the climate figurer look the transpiration charge per unit based on the difference in AH between the mood chamber and the glasshouse , corrected for fan speed , like the exemplar given in this post . This would be the ultimate rule of thumb in whether we are giving the plant a vegetal or generative impulse , and if we make the works work too hard . "
This clause is part of a series about grow in a semi - shut greenhouse . register here - go’sfor semi - closed greenhouse , cooling , the dispute between semi - closed and launching pad and fan glasshousesandhow to prevent momentumandbecoming a crop to vegetative .
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Godfrey DolLinkedIn[email protected]+81 80 700 94 006
