The effect of various growth mediums on the development and production of plants in hydroponics systems.
By Ben Safronovitz
In a trial conducted at Camdeboo Farm near Fourways, Johannesburg, South Africa, one basic question was posed. Are there any differences in the overall performance of plants grown in different growing mediums? …The reason for the trial is the general uncertainty (at least in South Africa) regarding growing mediums. Many growers are confused or reluctant to use some mediums due to a lack of experience, lack of performance information, and/or an ignorance regarding the financial implications of using the medium in the short- and long-term.
The main objective of a grower is to invest the minimum possible in infrastructure and achieving the maximum yield, which in financial terms means increased profit. Therefore, in the short-term, investing in an inferior growing medium is a reality. The fact is that a larger initial investment will in the long-run return an increased yield per growing cycle to warrant the investment, and yield a greater profit.
In South Africa sawdust as a hydroponic medium is used extensively; it is inexpensive, readily available from a nearby mill, and due to its low-cost, can be discarded after each growing cycle.
The importance of understanding the characteristics of a growing medium and the long- and short-term affect on the plant is essential to the overall success or failure of a crop, therefore the trial targeted the most commonly used growing mediums in the country, each on its own (to serve as a control batch) and also in combination with other growing mediums. Without elaborating on the physical and chemical differences among the tested growing mediums, each has characteristics, which make it a usable medium – for example: bulk density, porosity, aeration, ability to contact water with high holding capacity, highly hygroscopic, create capillary water and nutrients dynamics, etc.
The mediums used for the purpose of this trial were:
• Palm pith (Coir) 100%
• Perlite 100%
• Vermiculite 100%
• Sawdust 100%
• Palm pith 50% / Perlite 50%
• Palm pith 70% / Perlite 30%
• Palm pith 40% / Perlite 30% / Vermiculite 30%
• Perlite 50% / sawdust 50%
• A locally produced light compost pot soil 50% / Perlite 50%
Growing medium trials at Camdeboo Farm near Fourways, Johannesburg.
A standard tunnel 30m x 10m was selected for the purpose of the trial, positioned north-south with excellent light cover during the day. A white/black ground cover plastic sheet was used to eliminate weed growth and increase light reflection at the tunnel floor level, thus increasing plant photosynthesis.
Day one – seedlings transplanted into medium.
Medium consists of 50% palm pith and 50% Perlite.
Seedlings in 100% sawdust.
Seedlings grown in 50% pot soil and 50% Perlite.
Seedlings grown in 100% Perlite.
Seedlings grown in 100% Vermiculite.
Perlite 50% Sawdust 50%
The trial principles of using one crop (tomato), one cultivar (Malory – indeterminate variety produced by Mayford-Sakata seeds), under the same climatic conditions and nutrient feed and irrigation cycle regime across the various mediums, allowed a fair and unbiased evaluation of the plants’ performance during a complete growing cycle.
The hydroponics method used was quite revolutionary, which is in the process of patent registration. In essence, the method uses growing containers with a slit on one side at a certain level. This method allows routine irrigation (four times daily) of approximately 800 cubic centremetres of water and nutrients per plant on average, which has enormous implications on cost in terms of saving water and nutrients. The growing system was an open system (not re-circulated) and the drain kept to 10% of the total volume.
The floor plan was organised to allow for eight rows of 48 containers each. One block of 48 containers served as a control, representing each of the tested mediums. There were 432 containers with two plants per container, a total of 864 plants. Each medium covered a block of 48 containers situated along the tunnel width to ensure fair distribution of light or shade across the eight rows, eliminating the possibility of false results due to uneven exposure to light.