It is of human nature to always impose practical classifications in the common language over technical definitions, as we normally use in Mexico the anglicisms football and basketball for the their names in Spanish, balompie and baloncesto.
In my February editorial I was talking about the mistake of defining the word GREENHOUSE as a description of a structure rather than of a concept. Similarly, I believe that to classify the kinds of greenhouse as of high, medium and low technology falls into ambiguities and misunderstandings, and also suggests subconsciously that high is good and low is bad or inferior.
Let's see what I mean, for example, let’s try to define what is a high technology greenhouse and we will note that this does not explain specifically what components it must have to be classified that way; when I try to define it in the practical sense, I will use color black for its nature, and red the doubts that come out.
In the broad sense, it should be a metal structure covered with glass or polycarbonate, first doubt: if it is made out of plastic, is not high technology anymore? Or if it has a double layer of plastic with hot air cushion, is it high technology now? ... (Continuing with the definition) it should have a heating system, of hot water or air?, with CO2 injection, if it does not have these, is it not high technology? Or is it now of medium technology? Or medium – high or high – medium technology? It must be grown hydroponically, in mineral wool, perlite, coconut fiber, sand or peat moss? Which of these are considered as high tech and which are not? Can the soil in pots be considered? Are the grown-in-soil or organic crops featured? Or does it depend on the irrigation system? What if it is automated? Or is it not necessarily? Or does it depend on how much it costs
As we can see, there are many doubts in just these characteristics and we can go on with a line list of possible components
, such as heat screen, shading screen, fog, temperature sensor, relative humidity, radiation, wind speed and direction, automated control of ventilation, damp walls, extractors and air circulators, air curtains, artificial lighting, etc.
With so many questions I shelter in the technical aspects, in which I based for the definition of the CONCEPT OF GREENHOUSE in my last editorial. The ABC of a greenhouse is to control or modify the open field climatic variables: wind, solar radiation, rain, temperature, relative humidity and others, such as the entry of insects and moisture control and nutrient availability of soil or substrate.
Based on these variables is that there is a proper classification on the types of greenhouse, I must point out that I did not invented it, “the black thread was already invented”, as my former boss used to say and that is: active, semi active and passive greenhouse.
Active: The term refers to the fact that these modify or "participate actively" in the climate conditions, such as temperature, radiation, relative humidity, levels of gas exchange (CO2 and oxygen) and moisture and fertility of the soil or substrate. It is important to note that such equipment allows achieving an optimal control of variables. In practice, this type of greenhouse is used where it is required to grow all year and there is a climatic variable, which is essential to control it optimally in order to grow (commonly, it is the temperature, but currently in the Netherlands it led to light or radiation). The high investment required for such forces you to improve the other variables to retrieve or optimize your investment.
Semi active: It means those that are modified or “partially involved" in some climate conditions without necessarily achieving an optimal level, which means, by improving the conditions these may or may not reach the ideal performance. An example of this, are the areas where there are good environmental conditions in a time of the year, and these need to be modified at another time without being essential the optimal control, or that only some variables need to be modified in the crop cycle, in order to produce profitably, for example, in rain or warm temperatures.
Passive: This is one that does not get modified nor it "participates" in the climate conditions outside the radiation and thus, partially in temperature, wind influences relative humidity and insects from entering. This type of technology is used in areas where it is feasible to produce in open field seasonally, but with this tool it gives a better yield and quality.
It is important to emphasize that one is not exclusive of the other; there can be combinations, partial implementation or modifications of technologies, all with the aim of increasing the yield and quality to reduce costs or increase product value. There is an irrefutable law on greenhouse production:
“Any investment in technology that is done on a Greenhouse, is profitable in performance and quality “...It is just a matter of analyzing VERY WELL if this investment is cost-effective.
Cesar Campaña
Chairman of the Board
AMHPAC
