Diseases and Management of Crops under Protected Cultivation

(Diseases and Management of Crops under Protected Cultivation)
• Coarse medium is made up of larger particles with fewer, but larger spaces.
• A fine medium has many, but small pores.
• The size of particles and distribution of pores are important factors to determine the
physical characteristics of the medium.
• Total pore space and size determines the rate of drainage and gas exchange. A portion of
this space is occupied by air.
• Plant roots require oxygen for growth and adequate aeration of the medium is necessary. A
good soilless medium should have a good retaining ability of water, enough space for air
exchange, and good drainage rate. Following are examples of some growing medium:
I. Soil
• Soil media is the worst choice for growing greenhouse tomatoes because it does not
provide the optimum moisture and aeration at the same time.
• Disease, salts, and waste buildup in greenhouse soil is a limiting factor for long-term
profitable production.
• Repeated use of greenhouse soil to grow tomatoes will lead to significant losses because
of diseases, insect, and salt build-up
• It is not easy to sterilize greenhouse soil and there is no occasional heavy rain to wash off
excess salt and plant waste.
II. The Nutrient Film Technique (NFT)
• It is a water culture system where a shallow stream of nutrient solution covers the roots of
growing plants to provide water, nutrients, and oxygen.
III. Soilless media
• Rockwool, polyurethane, pine bark, and perlite are examples of soilless media that are
used for growing greenhouse tomatoes.
1. Pine bark
• Bark is a by-product of the timber industry.
• Before it can be used as a growing medium, it has to be composted to balance its
carbon/nitrogen content, get rid of the harmful compounds, and kill insects and disease.
• For successful composting, the bark must be thoroughly watered and conditioned with
nitrogen, then left to compost for at least three months with occasional turn over.
• During decomposition, compounds which inhibit growth are reduced and temperature
increases to about 150°F. Never use green pine bark to grow greenhouse tomatoes.
• It was a good growing medium if used for a maximum of two years. It was difficult to clean
the bark with hot water and reuse it indefinitely. Also, it was obvious to us that controlling
the pH in the root zone was not an easy task because of the continues decomposition of
the bark.
2. Perlite
• Perlite is a volcanic mineral crushed to small pieces and heated to 2000 °F.
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