CIFSRF CARICOMFood Security Project

This factsheet is a product of the CIFSRF CARICOM Food Security Project. The Canadian International Food Security Research Fund (CIFSRF) is a program of Canada’s International Development Research Centre (IDRC) undertaken with the financial support of the Government of Canada provided through Foreign Affairs, Trade and Development Canada (DFATD).

Soilless Media and Fertigation Basics for Caribbean Greenhouse Growers

Land & Water Resource Management. No. 4

September 2013

Soilless media (or substrate) has been used as an alternative to soil in protected agriculture systems because it helps to maintain a more controlled environment. Most substrates are pathogen free, and so reduce the risk of disease while improving productivity. A wide variety of substrates are commercially available. They can be used either singly or in combination to make different media. Importantly, soilless media should be formulated to provide optimal physical and chemical properties.

A good media should have:

Right density and porosity to allow for drainage, aeration and water retentionProper pHLow electrical conductivity (EC)Some nutrient supplying power (this is not absolutely necessary)No pathogens (sterilized)

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The table below describes important properties of common substrates used as media and media components in the Caribbean.

Description of Substrates used for Media

Substrate Physical Chemical BiologicalInorganic

Perlite Coarse texture,free draining, low water holding capacity (WHC), high air space Inert, good pH, low EC Sterilized

Vermiculite Coarse texture,free draining, medium WHC, high air space

High cation exchange capacity (CEC), chemically reactive, good pH, low EC Sterilized

Sand Fine-coarse texture, dense, free draining, low-medium air space Inert, good pH, low EC Dependent on source

Organic

Peat Coarse texture, high WHC, high air space, medium draining

High CEC, chemically active, nutrient retention, low pH, low EC

Dormant but microbes are present, none-few pathogens

Coir Coarse texture, high WHC, high air space, medium draining

High CEC, chemically active, nutrient retention, good pH, low EC

Dormant but microbes are present, none-few pathogens

Compost Medium-coarse texture, high WHC, medium-high air space, medium draining

High CEC, chemically active, nutrient source and retention, good pH, high EC

Very active, none-few pathogens if thermophilic (warmth loving)

2 CIFSRF CARICOM Food Security Project

Project trials showed that mixed media (combinations of organic and inorganic substrate) resulted in the best growth, development, yield and quality of tomatoes and sweet peppers. Combinations of perlite with peat, coir, or compost in a ratio of 3:2 have been used successfully. Combining inert, inorganic media with chemically-active, organic media neutralizes the limitations of individual substrates and enhances the positive characteristics. This does not imply that single substrates cannot or should not be used, as crop, environmental management and fertigation protocols also influence the behaviour of the media. Growers need to use diagnostic monitoring and testing tools and techniques to ensure that all properties are within acceptable ranges throughout the growing period.

Diagnostic tools used in greenhouse cultivation

FertigationFertigation remains the main means of satisfying plant nutrient requirements for greenhouse cultivation, especially where soilless media are used. Fertigation literally means ‘fertilization plus irrigation’. It has two main components: a micro irrigation delivery system, and a source of fertilizer nutrients supplied to the plant in appropriate quantities and at a frequency that will optimize productivity. Fertigation systems can employ either stock or bulk fertilizer tanks to supply the nutrients. Stock tanks require fertilizer injectors, which are expensive but have the advantage of allowing adjustments to the concentration of nutrients supplied. Both methods of nutrient supply are good, as long as the concentration of nutrients supplied is adequate. The following table provides a general formula (Hoagland’s Hydroponic Solution) that can be used; however, input suppliers have developed formulations for different crops. Growers should observe the crop and adjust the nutrient regime where necessary.

Hoagland’s Hydroponic Solution

Nutrient Concentration (ppm)N 210K 235

Ca 200P 31S 64

Mg 48Fe 1-5B 0.5

Mn 0.5Zn 0.05Cu 0.02Mo 0.01

Similarly important is the fertigation frequency. Different systems are available for managing the frequency and duration of fertigation events—from manual control, to timed delivery, to plant-based automated responses—with notable increases in costs. The benefit of more frequent fertigation has not been proven regionally, but maintaining optimal water and nutrient content in the media, especially during stressful periods, is vitally important. Increased fertigation events during these periods (high transpiration demand) are recommended. Increasing the fertigation frequency to greater than six times per day will have positive effects.