Plant response to greenhouse | plant response to greenhouse environment | planning and design of greenhouse | planning of greenhouse | design criteria of greenhouse | design criteria of greenhouse for cooling and heating purpose

Plant response to greenhouse

Plant response to greenhouse

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The productivity of a crop is influenced not only by its inheritance but also by the microclimate that surrounds it. The components of the microclimate of the crop are the light, the temperature, the composition of the air and the nature of the root medium. In open fields, the manipulation of the nature of the root environment is possible only by tillage, irrigation and the application of fertilizers. The closed limits in the greenhouse allow the control of one or more components of the microclimate.

1. Light

■ Visible light from solar radiation is a source of energy for plants. Light energy, carbon dioxide (Co2) and water enter the photosynthesis process through which carbohydrates are formed. The production of carbohydrates from carbon dioxide and water in the presence of chlorophyll, using light energy, is responsible for the growth and reproduction of plants. The rate of photosynthesis is regulated by the available fertilizing elements, water, carbon dioxide, light and temperature.

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■ The photosynthesis reaction can be represented as follows: Chlorophyll Co2 + water + light energy ------------ carbohydrates + oxygen Vegetable nutrients To reduce the carbon which combines with oxygen is needed in the gas CO2 as it exists in carbohydrates. The light energy used in this way is trapped in the carbohydrate. If the intensity of the light decreases, photosynthesis slows down and therefore growth. If higher than optimal light intensities are provided, growth slows down again due to damage to the chloroplasts.

■ Light intensity is measured in the international unit known as Lux. It is direct illumination of the surrounding surface which is one meter from a uniform point source of 1 international candle. Greenhouse crops are subject to light intensities ranging from 129.6 klux on clear summer days to 3.2 klux on cloudy winter days. For most crops, neither condition is ideal. Many crops are saturated with light, in other words, photosynthesis does not increase at light intensities above 32.2 klux. Rose and carnation plants will grow well in intense summer light intensities.

■ In general, for most other crops, the foliage is a deeper green if the greenhouse is shaded up to 40% from mid-spring (May) to mid-autumn (August and September). Therefore, it is clear that the light intensity requirements of photosynthesis vary greatly from crop to crop.

■ Light is classified according to its wavelength in nanometers (nm). Not all light is useful in the photosynthesis process. Ultraviolet light is available in the shortest wavelength range of less than 400nm. Large quantities are harmful to plants. Glass screens are opaque to most ultraviolet light and to light below the 325nm range. Visible and white light has a wavelength between 400 and 700 nm.

■ Far red light (700 to 750 nm) affects plants, as well as causing photosynthesis. Longer wavelength infrared rays are not involved in the plant process. It is mainly the visible light spectrum that is used in photosynthesis.

■ In the blue and red bands, photosynthesis activity is greater, when blue light (shorter wavelength) is supplied only to plants, growth is delayed and the plant becomes hard and dark in color. When plants are grown under red light (longer wavelength), growth is regular and internodes are long, which results in tall plants. Visible light of all wavelengths is easily usable in photosynthesis.

2. Temperature

■ Temperature is a measure of the level of heat present. All crops have a temperature range in which they can grow well. Below this range, the life process of plants stops due to the formation of ice within the tissue and the cells can be perforated by ice crystals. At the upper extremity, the enzymes become inactive and again the process essential for life ceases.

■ Enzymes are catalysts of biological reactions and are sensitive to heat. All biochemical reactions in the plant are controlled by enzymes. The rate of enzyme-controlled reactions often doubles or triples for every 100 ° C temperature rise, until the optimum temperature is reached.

HORTICULTURALS CROPS:-

Cinnamon (Daalchinni)

Mustard

coriander

Also, the rise in temperature begins to suppress the reaction and eventually stops it. As a general rule, greenhouse crops are grown at a daytime temperature, which is 3 to 60 ° C higher than the night temperature on cloudy days and 80 ° C higher on clear days.

■ The night temperature of greenhouse crops is generally between 7 and 210 ° C. Primrose, mathiola incana and calceolaria grow best at 70 ° C, carnation and cineraria at 10 ° C, rise to 160 ° C, chrysanthemum and poinsettia at 17 ° C to 180 ° C and African violet from 21 ° C to 220 ° C. 3. Relative humidity

■ Since the greenhouse is an enclosed space, the relative humidity of the greenhouse air will be higher than the ambient air, due to the added moisture from the evaporation and transpiration process.

■ Some of this moisture is removed from the air exiting the greenhouse due to ventilation. Sensitive heat inputs also reduce the relative humidity of the air to some extent.

■ To maintain desirable relative humidity levels in greenhouses, processes such as humidification or dehumidification are performed. For most crops, the acceptable relative humidity range is between 50 and 80%. However, for plant propagation work, relative humidity of up to 90% may be desirable.

■ In summer, due to the addition of sensible heat during the day, and in winter to increase the night temperatures of the greenhouse air, more sensible heat is added causing a reduction in the relative humidity of the air. For this, evaporative cooling panels and humidification misting system are used.

■ When the relative humidity is higher, fans, chemical dehumidifiers and cooling coils are used for dehumidification.

4. Ventilation

■ A greenhouse is ventilated to lower the greenhouse air temperature or to replenish the carbon dioxide supply or to moderate the relative humidity of the air. Air temperatures above 350 ° C are generally not suitable for greenhouse crops.

■ It is entirely possible to bring the air temperature of the greenhouse below this upper limit during the spring and autumn seasons simply by providing adequate ventilation of the greenhouse. Ventilation in a greenhouse can be natural or forced.

■ In the case of small greenhouses (less than 6m wide), natural ventilation can be quite effective during the spring and autumn seasons. However, fan ventilation is essential for precise control of air temperature, humidity and carbon dioxide levels.

5. Carbon dioxide

■ Carbon is an essential nutrient for plants and is present in the plant in greater quantities than any other nutrient. About 40% of the dry matter of the plant is composed of carbon. Under normal conditions, carbon dioxide (CO2) exits as a gas into the atmosphere slightly above 0.03% or 345 ppm.

■ During the day, when photosynthesis occurs under natural light, plants in a greenhouse reduce the CO2 level to less than 200 ppm.

■ Under these circumstances, infiltration or ventilation increases carbon dioxide levels when outside air is introduced to maintain CO2 levels in the environment. If the CO2 level is below environmental levels, the CO2 can retard plant growth. In cold climates, maintaining CO2 levels in the room by providing ventilation may not be economical, due to the need to heat the incoming air to maintain adequate growth temperatures.

■ In these regions, the enrichment of the greenhouse with CO2 is followed. The exact level of CO2 required for a given crop will vary as it must be correlated with other variables in greenhouse production such as light, temperature, nutrient levels, crop and degree of maturity. Most crops will respond favorably to Co2 from 1000 to 1200 ppm.

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