Current Category » Introduction to Horticulture
Mist Propagation of Herbaceous and Softwood Cutting:
Mist propagation consists of maintaining a film of water on the leaves of the cutting and relative humidity of the ambient air. In this way, the rate of transpiration is reduced to a minimum and as result the guard cells remain turgid. The stomata’s remain open, and the manufacture of carbohydrates and related substances proceeds unabated even in presence of high light intensity. Further, with the high light intensity, the evaporation of water from the leaves keep the tops relativity cool, and this in turn lowers the rate of respiration. Thus, with the low rate of transpiration combines with the low rate of respiration, other manufactured substances become available for the initiation and growth of the root system.
There are Two Kinds or Types of Misting:
i) Continuous and
The continuous involve applying the mist continuously during the light period, whereas the intermittent system involves applying the mist at definite intervals during the light period. Each system has advantages and disadvantages. The main advantages of the continuous system. Its main disadvantages is that excessive leaching of soluble compounds from the leaves is likely to take place and unless the media is well drained, water logging of the media is likely to occur. The main advantages of the intermittent system are that excessive leaching of soluble compounds from the leaves and water lagging of the media is likely to occur. The main advantages of the intermittent system is that excessive leaching of soluble compounds from the leaves and water logging of the media is not take place. Its main disadvantages are that a timing mechanism is required to control the misting cycle. Thus, the advantages of the one come the disadvantages of the other. However, a research survey of system through the world shoes that the intermittent system is the delier used. Of a total of 1,105 installations 729, or 66 percent, used the intermittent system, and 376, or 34 percent used the continuous system.
In general, five system have been development to control the misting cycle of the intermittent system. Of these five systems, three are three used in commercial installations. These are 1) misting cycle time clock, 2) electronic leaf, and 3) Mistomatic, the electric time clock consist of a day night clock and a misting cycle clock connected with a solenoid valve. The day night clock turns on the system in the morning, usually just after sunrise, and off in the evening, usually just after suset, the misting cycle clock turns the system on and off for definite intervals during the day, for example, a commonly used misting cycle is one minute with the clock set to mist the cutting for three, four, or five or more seconds per minute. The main advantages of this system is that it has a relatively low installation and Maintences cost. Its main disadvantages are that manual operations required to change the misting cycle.
The so called electronic leaf consists of a piece of plastic with two electrodes and a control unit connected to a solenoid valve. It is based on the assumption that the evaporation of water from the leaves. When a continuous d\fixed exists between the two electrodes, misting is considered to be unnecessary and the solenoid valve is then the closed position. With the evaporation of water between the electrodes, the film evaporates, contact between the electrode is broken, and the solenoid valve opens and misting begins. Thus, the main advantage of this system is that the period of misting varies with the rate of evaporation and transpiration of waster from the leaves, which varies according to temperature and light intensity. In addition no manual control is necessary. Its main disadvantages is that mineral salts may gradually accumulate on the electrodes, eventually forming a continuous film between the electronodes which claim would close would close the solenoid valve.
The Mistomatic system consists of a small stainless steel or grid and a control unit connected to a solenoid valve. Here again, this system operates on the assumption that the rate of evaporation of water from the screen or grid is practically the same as the rate of transpiration and evaporation of water from the leaves. When the mist is falling on the cutting, it is also failing on the grid, which gradually declines to a point where the mercury switch closes the solenoid valve and misting stops. With loss of water from the leaves and corresponding loss of water from the grid, the grid gradually rises to point where the switch opens the solenoid valve and misting begins. Thus the operation of the Mistomatic system is similar to that of the electronic leaf system, and its main advantages and disadvantages are practically the same.
Misting propagation structure includes which were used before the misting technique as developed and structures especially designed for the misting technique. Example of the former are greenhouses, plastic houses and lath houses, and examples of the latter are low lying, Quonset type plastic tents, close or open topped rectangular frames. Mist boxes and the so called bubbles. In all of these types, the rooting media are placed on level and well drained soil to prevent water logging and to provide adequate aeration of the media, and the covers are movable to regulate the temperature within the enclosure and more particularly, to requital the light intensity impinging on the leave s. for example when a lot a cutting become established that is as they develop their root systems, the light intensity can be safely increased. In addition the farmers and boxes have sides consisting of light transmitting plastic to protect the cutting from strong winds bottom heat is necessary, a thermostatically controlled heating cable is placed directly under the rooting media.
Current Category » Introduction to Horticulture