the growing of plants there are fundamental aspects which need to be fulfilled to allow
the plants to grow and develop to their optimal genetic potential:
• light (typically sunlight as a source of energy for photosynthesis)
• temperature (suitable range for plant type)
• space (density to allow air, light and growth and development of the plant)
• Carbon dioxide (for photosynthesis)
• water (for essential plant processes)
• oxygen (supplied to root zone for optimal root function)
• nutrients (growth and development), and
• the provision of a growing environment devoid of plant pests, pathogens and weeds.
Water retention efficiency (WRE) is a measure of the ability of a growing media to hold water applied from irrigation and this influences how long the irrigation must be run to wet up the media. An Australia wide survey
has shown that the WRE of commercially available growing media varies considerably, and suggests that the choice of growing media can influence water consumption and the quantity of nutrient runoff produced from a sprinkler or drip irrigation system.
Water retention efficiency (WRE) is a measure of the ability of a growing media to hold water applied from irrigation and this influences how long the irrigation must be run to wet up the media. An Australia wide survey
has shown that the WRE of commercially available growing media varies considerably, and suggests that the choice of growing media can influence water consumption and the quantity of nutrient runoff produced from a sprinkler or drip irrigation system.
In last week’s article we mentioned briefly that nurseries should have the correct physical, chemical and biological properties in their growing media. The question is have you actually tested them on site? Listed in the back of “Container Media Management” by K.Bodman and Dr.K.V.Sharman, 1993. This is a complete guide for nurseries to analyse their growing media. It discusses the analytical methods for determining Air Filled Porosity, Total Water Holding Capacity, Wettability, Volume and Bulk Density, pH and EC (Electrical Conductivity), Toxicity Index and Nitrogen Drawdown Index.
Understanding pH management starts with your choice of growing media components, the crops you choose to grow in them and how you intend on irrigating them. Currently there is a wide range of media components available to the nursery industry. They may include but are not limited to: pine bark, peat, coir, sand, perlite, vermiculite, absorbalite, peanut shell, rice hulls and the list goes on. Some decisions on which components to use are dictated by what is available locally and for some it may be the cost of the growing media landed on your property.
Coir or coconut fibre is the fibrous material that exists in the middle layer (mesocarp) of the coconut fruit. The long coir fibres are extracted from the coconut husk and used in the manufacture of brushes, twine and other products, while the short fibres have been shown to have excellent physical properties which can contribute to significant growth benefits for nursery plants.
In response to requests by production nurseries in Far North Queensland (FNQ) for industry hands-on workshops about the use and testing of growing media in production nurseries, two Growing Media Workshops were held in May 2013 in Cairns and in the Atherton Tablelands. Both workshops were presented by Thea Pobjoy, the Northern Queensland Farm Management Systems Officer (FMSO) for the Nursery & Garden Industry Queensland (NGIQ).
The ability of a growing media to take up water effectively once it has dried out is critical to the growth of plants and the ability of the media to become wet again. This is known as wettability. Testing for wettability isn't difficult and can be done at minimal cost with some basic equipment
Knowing the amount of water held within a growing media, referred to as Water Holding Capacity (WHC) of your growing media can help you manage irrigation scheduling more effectively and ensure plants have adequate moisture.
The Water Holding Capacity (WHC) of a growing media measures the amount of water that a growing media can hold without causing plant stress. The WHC is largely determined by the amount and type of pore spaces available in the growing media, however the height and shape of the growing container also influences the growing media’s WHC (see Container Media Management; K. Bodman & Dr. K.V. Sharman which can be purchased from NGIQ). EcoHort guidelines recommend a WHC of greater than 40% (see EcoHort Guidelines from NGIQ).
Water Holding Capacity Testing
The Water Holding Capacity (WHC) of a growing media measures the amount of water that a growing media can hold without causing plant stress. The WHC is largely determined by the amount and type of pore spaces available in the growing media, however the height and shape of the growing container also influences the growing media’s WHC (see Container Media Management; K. Bodman & Dr. K.V. Sharman which can be purchased from NGIQ). EcoHort guidelines recommend a WHC of greater than 40% (see EcoHort Guidelines from NGIQ).
Air filled porosity (AFP), water holding capacity (WHC), bulk density, shrinkage, wettability and water retention efficiency (WRE) are all physical properties of growing media that influence plant growth and ultimately plant health.
Air filled porosity (AFP), water holding capacity (WHC), bulk density, shrinkage, wettability and water retention efficiency (WRE) are all physical properties of growing media that influence plant growth and ultimately plant health.
An understanding of the physical, chemical and biological characteristics of a growing media can improve plant growth and your bottom line. In this article we look at the physical characteristics of growing media.
Air Filled Porosity - AFP.
AFP is the percentage of the growing media occupied by air after the media has been saturated with water and allowed to drain. More air in the media will improve root growth, but a higher AFP may require more frequent watering and consequently nutrient leaching may be increased. Container depth has a significant effect on AFP as, in shallow containers, the AFP is reduced due to the greater proportion of media occupied by the saturated media in the bottom of the container. AFP will also decrease during the growing cycle, but this can be compensated, to a degree, by the increased ability of the plant to extract water from the growing media, reducing the amount of pore space occupied by water. A range of 13-30% AFP is considered to be acceptable under EcoHort guidelines for general nursery stock.
The pH measures the hydrogen ions in the growing media, while EC (electrical conductivity) measures the soluble salts in the mix. For optimal plant health, the pH and EC of the growing media should be in accordance with the plant’s requirements because different plants can have different preferred pH and EC ranges (see Container Media Management; K. Bodman & Dr. K.V. Sharman which can be purchased from NGIQ).
The pH measures the hydrogen ions in the growing media, while EC (electrical conductivity) measures the soluble salts in the mix. For optimal plant health, the pH and EC of the growing media should be in accordance with the plant’s requirements because different plants can have different preferred pH and EC ranges (see Container Media Management; K. Bodman & Dr. K.V. Sharman which can be purchased from NGIQ).