Greenhouse Technology

Greenhouse Technology : Introduction

The agricultural country like India, Sri Lanka, Unite states, Unite Kingdom, Canada, Spain etc. has a variety of problems in agricultural itself.

In spite of the 80% of population depending on agricultural, our farmers cannot produce sufficient food, grains, oilseeds, pulses, vegetables, fruits, etc.

Agriculture industry is the largest industry in India, Unite states, Unite Kingdom, Canada, Spain and other nearby countries, but still it’s output is not satisfactory. Majority of the farmers are below poverty line.

The growing population and agricultural production are not matching.

The environment degradation, global warming, drastic changes in climate desertification of soil, depletion of groundwater, shortage of rainfall urbanization, Pollution etc. have created many problems for agricultural development in all over the world.

To get rid from all such problems we have to use high-tech technology in agriculture.

Due to the recent policy adopted by the state government and central government nowadays, farming is rapidly changing in the world.

Farmers are using various advanced techniques such as plant tissue culture technique, dry farming technology, greenhouse technology, etc. The high tech cultivation practice includes use of Poly house, greenhouse and shading Nets.

Greenhouse cultivation or plasticulture is becoming very popular in farmers engaging horticulture, business or the farmers cultivating exportable cut flowers like rose, gerbera, etc.

Greenhouse Technology : History

Plasticulture (Growing plants under cover) technology has developed over last two centuries in some part of Globe.
The Romans were the first to grow the desert fruits under thin sheet of mica called ‘mercury glass’.
Bois De Puc in France, is the first who has grown flowers in glass pavilions. Later on, green houses were constructed in Apothecaries garden, Chalsea, England, etc.

The term green home or greenhouse was coined by John Evelyn in 1658.
In the 19th century, a concept of greenhouse has spread throughout the England. By the middle of 19th centuries, all the techniques needed for successful greenhouse gardening has been developed. Today, variety of green houses are available in all over the world.
Nowadays in whole world cultivation of cut flowers, fruit plants like strawberry, vegetable crop like tomato, cucumber etc. in greenhouse is also becoming popular.

Most of the green houses are covered with the polyethylene film, hence known as Poly Houses.

Greenhouse Technology : Concept and Definition

A greenhouse means area or a house in which plants are grown under artificial controlled climatic conditions, so that light, temperature and humidity are maintained at required level.

Effect of this specific microclimate on the growth and productivity of crop is commonly known as effect of greenhouse.

A greenhouse is a framed structure covered with transparent or translucent material in which crop can be grown under the condition of partial or fully controlled environment, and which are large enough to allow a person to walk within them and carry out cultural operations.

A technique of cultivation of plants of commercial value in polyhouse is known as plasticulture. This protected cultivation of plant is also referred as greenhouse cultivation.

Principles involved in greenhouse technology

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Light Intensity

It provides required intensity and wavelength of light for maximizing the rate of photosynthesis.

The transparent plastic cover only required radiation for photosynthesis are allowed to pass through it.
The range of required solar radiations is 0.32 to 2.5 micron. All other radiations (higher than 7 microns) cannot pass through the plastic cover.

Temperature

It maintains required temperature range for the healthy growth of plants.

The maximum temperature inside the Poly house should not exceed 20 degrees Celsius – 30 degrees Celsius and low temperature range is 5 degrees Celsius – 10 degree Celsius, hence artificial cooling and heating is provided to maintain the required temperature range. This range varies from crop to crop.

Humidity

Greenhouse provides required range of relative humidity between 40% to 75% to the plant.
This range of relative humidity is beneficial for most of the greenhouse plants.

However, exact level of required humidity will depend on the types of plants grown and the range of temperature of Poly house. The required humidity is maintained by the evaporate cooling by fog system and closing or opening of ventilators.

CO2 concentration

Optimum concentration of carbon dioxide is maintained in the Poly house to achieve the highest rate of photosynthesis.
During night, carbon dioxide is released by the plant through respiration. This carbon dioxide accumulates in the surrounding of the plants (minimum and optimum level of carbon dioxide is 300 PPM to 1500 PPM).

This increased level of carbon dioxide increases the rate of photosynthesis by two to three times and hence ultimately the growth and yield of crops grown in polyhouse increases.

Soil Type

Greenhouse provides ideal soil condition to the crop.
The soil pH is maintained at 6 to 7.5. The soil temperature ranges in between 20 degrees Celsius to 30 degrees Celsius and the humidity level between 60% to 65%.

Disease free condition

Greenhouse provide pets and disease free conditions.
Due to the close condition, plants are protected from the attack of various insects and pathogens.
It avoids the use of pesticides and fungicides that thereby improve the quality standard required for export of the agricultural procedure.

Site selection for greenhouse

The selection of location is most important for erecting greenhouse.

The location should be guided by three basic factors.

Cost of production

Cost of transportation
Desired quantity of product.

The importance of critical analysis of the various location factors such as climate, soil, water, communication facilities, availability of power, raw material, labor and the basic infrastructure are also essential.

The suitability of land should be taken into consideration between erection of greenhouse. The land under use or greenhouse should be minimum visible size, including extra space for utilities and expansion.

The other important factors are road approach orientation of the plot, shape of the plot, the level of the plot. In addition to all these, the land price is ultimately determines the choice of location.

Site selected for construction of greenhouse should be with proper drainage, well connected roads, continuous electric supply, and with perennial water sources. The proposed site should not be located near an industrial emitting pollutants.

There should be sufficient room for the expansion of the facilities in the future.

To protect greenhouse from strong winds, they should not be located in hilly areas and there should be deep tall vegetation, at least at the distance of 30 meters to waste-east direction.

Greenhouse Technology : Necessary Elements

Climate Condition

Effect of climatic conditions are deciding factor in success of greenhouse business.

Construction should depend on the local climatic conditions like. Intensity of sun radiation, humidity, rainfall, temperature, wind velocity, and other facilities in that area.

The area where inclement whether or shadow from the northern slope of Fall Mountain area are poor for crop growth.

Most important and influencing factors are temperature and humidity.

Gerbera (Temperature = 17 to 25) (Humidity = 65 to 80%)
Rose (Temperature = 17 to 25) (Humidity = 70 to 85%)
Authurium (Temperature = 25 to 30) (Humidity = 75 to 90%)

A need for greenhouse ventilation arises for the control of parameters such as temperature, relative humidity, carbon dioxide concentration, and air circulation around the plant.

Temperature should be maintained between 18 to 30 degrees Celsius.

The relative humidity between 60 to 70% for the better growth of the floriculture and other crops.

There are two methods for ventilation, natural and forced ventilation.

Natural Ventilation – The sufficient open space to side, front, end, and top of the greenhouse is provided for effective results.

Ventilation area should be 20 to 30% of the floor area. Minimum height of greenhouse for effective ventilation should be 3 to 3.5 meter. In climates where temperatures can sink considerably in the night, ventilation must be closable.

For controlling the required temperature and relative humidity, evaporative cooling system viz. high pressure mist system and fan and pad system are in practice. In high pressure mist system, water is sprayed into the air about the crop. A mist fills the greenhouse atmosphere cooling the air as it evaporates. It is more effective during the warmest part of the day. According to the size of the greenhouse, the pad and fan system is designed.

Carbon Dioxide Enrichment

Carbon dioxide in relation to plant growth is very important factor.
In the process of photosynthesis a plant leaves prepare food by using CO2 and water in the presence of sunlight to form carbohydrates and oxygen. This process happened naturally in the open fields without any concern of the CO2 availability.

The atmospheric air contains about 0.03% CO2. This level of CO2 in the air is normally sufficient to meet the needs of crops photosynthesis under open field conditions.
In Greenhouse initially before Sunrise, a CO2 concentration is 1000 PPM due to the respired CO2 trapped overnight. The increased concentration of CO2 is utilized at day time for photosynthesis and this rate is increased by three to four times more than the open space.
For better photosynthesis rate, the provision of enrichment of CO2 must be made in the greenhouse.

There are different methods for enrichment of CO2,

Combustion
Liquid CO2

Solid CO2

The general range of supplying CO2 in the greenhouse is between 0.6 to 1.2 liter/hour/meter of floor area.

Water Sources

Ideally, greenhouse needs one Lac liters of water per hectare per day.

Water should be free from salts and it should be clean. Source of water is highly essential. As the evaporation from the soil also occurs inside greenhouse, it raises humidity. Consequently, less irrigation is required in greenhouse.
Mostly drip irrigation system is installed for watering the crops in greenhouse after watering 10 – 20% of the volume of root medium should be occupied by the air and 35 to 50% by water that is high moisture retention coupled with good irritation.
Sufficient quantity of good quality water should be available for good crop development and yields. Designing of specific irrigation system is very essential. For that quantity of water for irrigation should be estimated and ensure its availability. Quantity of water available for irrigation must be confirmed.

Electrical conductivity and total soluble salt value of available water should be tested.

Soil Condition

The well drained and fertile soil is needed for greenhouse. If the soil is non fertile a mixture of loam soil, composed and Paddy husk is used.

Soil provides essential elements for the growth, hence known as growth medium. Soil based medium containing 25% or more soil. Panic matters of the soil mainly include composed farmyard manure.

Concentrated organic manners oil cakes, cattle, pig and poultry manures, meat, fish meal, etc. The other organic matters in route media are manual wood residue, sawdust, woodchips barks, rice, straw, etc.

Structure of Greenhouse

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Structure of greenhouse depends on the purpose and site where it to be constructed. It must be light and strong enough to withstand various forces.

Structure of greenhouse is semi permanent structure. A greenhouse structure must resist loads as like it own weight, wind, snow, etc. It must permit maximum light transmission so that it provides favorable microclimate to the crop grown in it.

A greenhouse should be designed in such a way that it could resist a wind velocity of 100 km/hrs.

Structure of greenhouse also depend on root shape, number of span, used in it and weather climate control or climate controlling it.

While considering this entire factor greenhouse constructing cost should be affordable.

While constructing a greenhouse for wing four, structural components should be taken into consideration.

Foundation
Floors

frame
Glazing

Foundation of greenhouse

It is important as it provides, anchorage to the super structure and supports it against the different forces.

Pit foundation is common method used in greenhouse construction as it is structural members are widely spaced.
The depth of the pit foundation should be a minimum of 60 cm and it should rest on undisturbed soil.
To provide sufficient strength the pit-diameter has been made related to the greenhouse span. Continues foundation is important where hoops are closely spaced.

A Curtain wall is constructed from ground level to about 30 to 50 cm in the green house area. Curtain wall is not essential in simple constructions.
Foundation must be made up of RCC, galvanized steel, Pleated wood or concrete masonry.

Floor of greenhouse

Ground floors are prepared for good drainage and weed control where the crops are not being grown in the ground soil.

Porous concrete can be used as a good alternative for greenhouse floor.
For preparation of 1 cubic meter of concrete mixture of 10mm aggregate: 1275 kg + Sacks of cement 5.5 + Water 90to 91 liters us used.
Sand is not used in the mixture. The mixture is uniformly placed on a well drained base of sand or gravel.

A 10 centimeter thick floor of porous concrete is sufficiently strong for greenhouse use. When the crops are to be grown in the ground soil floor is of fertile well drained sterilized soil.

Frame of greenhouse

Steel, wood, bamboo, aluminum and reinforced concrete are the common materials for frame construction.
Wood is treated for protection from high moisture condition. The frames are painted for better light.

The chemicals being used in the wood treatment should not be toxic to either plants or human beings.
Normally, a coal tar is used as a preservative for underground portion of wood.
Chromated Copper Arsenate (CCA), and Ammonical Copper Arsenate (ACA) are two water borne preservatives are safe for use in the greenhouse.

The steel components of the frame should be hot dipped galvanized to avoid resting. Metallic frames with white paint improves the light condition in greenhouse.
A more sunlight can transfer by steel or an aluminum frame in compression to the wooden frame. Bending hoops and other components in the greenhouse is needed.
A pipe machine is recommended for giving the curved shape to the structural components.

Generally, a framework of a greenhouse is made up of smooth surfaced aluminum or steel angles of suitable size. Sometimes processed bamboo are also used. The size of single panel should be 5m:3m:3m or 8m:3m:5m.

Glazing of greenhouse

Glazing is nothing but covering of greenhouse frame with transparent plastic or glass.
Ultraviolet stabilized polyethylene is well known glazing material due to its good service and low cost. It consists of 200 Micron film and lasts for more than two years.

In order to avoid puncturing by nail or any sharp object double layer polyethylene film are attached to greenhouse frame. These films should be colorless and transparent.
If glass fiber or acrylic sheets are used, its transparency should be 80% to 90%.
For connecting sheets of film, head sealer should be used. Polyethylene sheets allow about 90% of the radiation between 0.25 to 0.32 nm to pass through and stop all radiations higher than 7 nm.

If the shade net is used for the roof, it’s transparency should be 30% to 75%.
Shape of the loop varies according to climatic condition of the area. When light is passed through glazing material, a beam of radiation is incident on a material. The radiation absorptivity, reflectivity and transmissivity values depends upon the material composition.
A transparent material transmits a large portion of light through it. Where as an opaque material either reflects or absorbs the incident radiation.

Types of Greenhouse

Greenhouse based on the material used for roof

Various materials are used for covering of green houses. Normally a greenhouse with the rope of polyethylene sheet or plastic film Poly-vinyl chloride (PVC) sheets is known as Poly House.

Poly House made of plastic film, especially used in the tropical and subtropical areas. They are economical as compared to glass and fiberglass. Poly houses made with low density polyethylene or linear low density polyethylene stabilized with ultraviolet absorber will last for a period of three to four years as compared to polyethylene without ultraviolet stabilization.

If roof of greenhouse is made up of glass it is known as Glass House.

Hoop Type : These are the structures with arched (dome-shaped) roof. Height is normally 1.8 meter. It is tunnel shaped, constructed by bending steel pipes or bamboo. They are used to protect the plants from cold and frost for very short periods.
Gable Type : In this type roof is inclined on both sides. Sides and tops are covered with polycarbonate or Polysheets. Normal size is 8.7 meter wide and 28.8 to 30 meter long. It is most suitable for temperature region.
Quonset Type : In this type of greenhouse, roof is semi round. Roof and sides are covered with polyethylene sheets. The ideal size is 28.8 meter – 36.8 meter in length, 8.7 meters in width, 2.4 – 3.0 meter in sides, and 3.6 – 4.24 meter in height at the center. It requires less roofing material.

Gothic Arch Type : In most of the countries in the globe Gable roof and hoop type single or multi span greenhouse are common.

Greenhouse based on inside climate

Climate control greenhouse

It is also known as environment controlled greenhouse.
It is completely closed greenhouse having system of controlling temperature, light intensity, humidity due to which specific microclimate created.

These type of Greenhouses are used to grow only high value crops all round the year.
It is also useful for hardening of tissue cultured plants. In the colder area, temperature inside the greenhouse is maintained higher than external temperature than it is known as warm greenhouse.
In other places where Summers are extremely hot, temperatures in the green houses is less than external temperature than it is known as cool greenhouse.

Partially climate controlled greenhouse

It is a greenhouse open from sides and at the roof by scientific ventilating area.
These green houses provide with near optimum conditions of temperature and relative humidity for growing the plants. These are simple structures as compared to climate controlled greenhouse.
Some flower flower crops and vegetables can be grown in this type of green houses during winter and rainy seasons in place having relative mild climatic condition.

These green houses are not suitable for cultivating the crops during the summer as the temperature cannot be regulated.

Advantages of Greenhouse Technology

Greenhouse causes greenhouse effect on the plants that increase the rate of photosynthesis by increasing CO2 concentration around the plant.
CO2 concentration in the atmosphere is 300 PPM while in greenhouse it is up to 1500 PPM. So plants show, vigorous growth and productivity of plant increases 3 to 4 times.

Maximum production can be obtained in small area.

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Applications of Greenhouse Technology

Increasing the agricultural product churn and improving the quality of the agricultural products. The main objectives are

To provide high quality product to the consumer that cannot be grown outdoors at that time of the year at a given place.
To protect the crop from high as well as low temperatures and from rainfall.
To have the timely harvest and also improves the quality of the product.

To increase the yield of the crop for better crop management.
To increase harvesting pride and to increase the plant population per unit area.
To grow crops in off-season and get the higher return.

By maintaining relative humidity less than 90% and by pruning healthy and productive plants can be maintained.

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Limitations of Greenhouse Technology

Capital investment for the erection of greenhouse is very high and hence it is beyond the reach of small farmers or poor farmers.

It requires trained and skilled laborer, knowing the crop cycle and as well as technology of greenhouse.
The cost of planting material is very high as the plantlets are raised through tissue culture.

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