Controlled Environments

Man cannot quietly adapt to the existing environrnenta1 conditions of his agricultural areas. He has altered these conditions by clearing the land of unwanted species, controlling weeds, increasing soil fertility and providing water by means of irrigation. Man has also been actively developing crop varieties which are better adapted to various environments.

With the ever-increasing demand for food, knowledge of plant response to the environment has become more and more important. Greenhouses or glasshouses, plant-growing chambers and phytotrons are used to obtain answers to many problems now facing the agricultural science, the most important of them being the determination of maximum yield that is possible and optimum conditions for maximum growth.

The controlled-environment rooms have become very important in biological research. They are important in obtaining biological knowledge to improve agricultural practices and produce.

Controlled environments for plant growth serve several purposes:

1) to determine how environmental factors affect plant development; what factors should be controlled and when such controls are useful and/or necessary during the life-cyc1e of the plant;

2) to establish the maximum yield that farm crops can be expected to produce;

3) to supplement field research in plant breeding and the introduction of new crops;

4) to provide conditions useful for biochemical and physiological investigations which can give necessary information for solution of agricultural problems;

5) to understand how environment affects pathogenesis, and some others.

Much investigation of environment control is stil1 carried out in the field through irrigation, weed control, fertilisation and frost prevention.

Plant-growing chambers and phytotrons provide most ideal conditions for plant growth, but now they are not used for commercial production but only as a means of research. Growth chambers, and especially phytotrons, provide a rapid means for determining the growth potential of plants.

The term plant-growing chamber is used to describe all kinds of controlled-environrnent facilities. There are many different types of plant-growing chambers. Some of them are large and man can work inside the chamber. Such chambers are known as reach-in or walk-in cabinets. Some are small. In this case man can work with his hands in. There are special-purpose chambers such as dew chambers, seed germinators, photoperiod rooms and others.

Chambers are usua11y constructed so that they can be used for a specific research purpose or for a particular kind of plant. There are chambers for carrying out plant disease investigations, for photosynthesis study, for soil atmosphere studies, for air-pollution research.

The chambers can be naturally-lighted or artificially lighted. The major changes that have taken place in plant growing chambers have been a resu1t of lighting systems. Different types of lamps are used in chambers. Fluorescent lamps are considered to be exce11ent light sources that provide good plant growth. Fluorescent lamps are usually mounted vertically on the walls as well as on the ceiling. During the last years some other kinds of lamps were suggested. They are sodium lamps and Xenon ones. Experimental data on the biological effectiveness of the former are at present inadequate to establish their role in controlled environments. As far as the Xenon lamp is concerned, its use is limited due to high costs as well as to some technical difficulties.

Temperature and humidity are also controlled in all types of plant-growing chambers.

Phytotrons are the most complex form of controlled environments, since they are composed of many types of plant-growing chambers. Artificially- and naturally-lighted plant-growing chambers and cabinets may be used in conjunction with seed germinators, dew chambers, photoperiod rooms and other controlled environments.

The keyfeature of a phytotron is the method of operation. Various forms of controlled-environment rooms, such as greenhouses, growing chambers, germination rooms, etc. are accumu1ated in one location so that plants can be moved from one environment to another. A phytotron is

therefore so organised that many combinations of environmental factors can be studied simultaneously and it is this organisation that defines the phytotron. Phytotrons differ both in design and in their research purposes.