A greenhouse is a closed structure, covered with translucent materials, that creates optimal climate, water, pest control, soil fertility and ventilation conditions in order to attain high productivity more quickly, at lower cost and with less of an environmental impact. Climate variables inside the greenhouse are controlled with several devices and materials including, inter alia, shade mesh, windows and openings, forced ventilation and humidifiers. The shape of the structure and the material with which it is covered will vary according to the specific purpose (for example, germination).
The following land-related issues should be considered before installing a greenhouse: fertility (the soil’s physical, chemical and microbiological condition); drainage capacity; availability and proximity of a source of water for irrigation; access roads; ventilation requirements, including wind direction; light (avoid locations near high trees); slope (flat topography is ideal); and orientation (amount of solar irradiation).
Threats and Impacts it Addresses
By providing a space with the most suitable microclimate for cultivation, greenhouses diminish the impact of changing rainfall patterns, strong winds, hail, frost and extreme heat. This raises productivity, avoids crop damage and failure and improves food security.
- Site the greenhouse taking into account the factors described above and the characteristics of the crop.
- Design the greenhouse with dimensions no greater than 10 to 12 m wide by 60 m long, to facilitate crop management. The smallest fixed opening in the roof should be between 30 and 40 cm high so as to permit adequate ventilation.
- Assemble the structure and cover it with the selected material. The structure may be made of wood, guadua, iron, galvanized steel, aluminium, PVC or a combination of these materials.
- Install removable curtains at the front and on the sides to regulate relative humidity while continually monitoring climate conditions.
- Prepare the crop beds and sow.
Inputs and Costs
Construction of a 500 m2 greenhouse for tomatoes. The main expense is the purchase of materials, particularly polyethylene rolls for the cover and the planks and posts for the structure. The installation labour will also entail expenses. Three days’ training in greenhouse operation and maintenance are considered.
|500 m2 greenhouse
Economic and Ecosystemic Benefits
A greenhouse can increase crop yields by shortening growing cycles and raise crop quality through a controlled indoor atmosphere. A tripling of yields in tomato crops has been observed, from 40 t/ha in outdoor cultivation with modern methods compared with 120 t/ha in a greenhouse (Jaramillo, 2006). At this level of output, the system for which the estimated costs are given above could produce six tons of tomatoes per crop cycle. Other benefits include the preservation of the soil's structure and nutrients. In the greenhouse’s protected environment, the soil remains firm and is not eroded by rain or wind.
Greenhouses require a high initial investment and skilled workers, and they are also expensive to operate. Internal ambient conditions must be constantly monitored to ensure proper pest and disease control. The spread of a pest or disease within a greenhouse may damage the entire production in 24 hours, which usually does not occur with outdoor cultivation. Strong rain and wind, as well as hail, may damage the cover material.
Greenhouse crops, because they grow under optimal conditions, generally command a higher market price as a result of their appearance, weight and size. The notion that greenhouses are not exposed to insects or disease is erroneous. The internal environment is highly conducive to pest propagation. The type and model of the greenhouse must be in keeping with the producer's financial possibilities. The cover material should be durable and easy to maintain.
Global warming has raised temperatures in greenhouses. This requires new models to be devised with more internal space and larger ventilation areas, as well as implementing stricter phytosanitary controls of crops. Regular maintenance of the structure and cover is important, and the greenhouse must be inspected before the rainy or windy season. For greenhouses to be considered as an ecosystem-based adaptation option, additional measures, such as organic fertilization, drip irrigation, or integrated nutrient management should be considered.
Units to Monitor Project Progress: Area of greenhouses built (m2).
Unites to Monitor Measure's Impact: Production (t/ha); operating costs (US$/ha).
- Escobar, H. and R. Lee (2002). Producción de tomate bajo invernadero. Bogota: Universidad Jorge Tadeo Lozano, Centro de Investigaciones y Asesorías Agroindustriales (CIAA), Colciencias.
- Jaramillo N., J.E. and others. (2006). El cultivo de tomate bajo invernadero. Boletín Técnico No. 21. Corpoica. Centro de Investigación La Selva. Rionegro, Antioquia, Colombia.
- Barrios, C. (2004). Construcción de un Invernadero. Fundación de Comunicaciones, Capacitación y Cultura del Agro FUCOA. Ministerio de Agricultura. Santiago, Chile.