It’s now more than 35 years ago that growers of fruit vegetable crops in western Europe started to use substrates as alternatives to natural soil. The many years’ searching of researchers and product developers had the desired outcome. Stonewool especially proved very promising. Propagation blocks and slabs made of this material, which is highly porous but at the same time also very sturdy, offer fruit and vegetables a stable rooting medium in which they will find sufficient water and nutrients throughout their entire development to ensure uninterrupted growth and high production volumes. Coco coir and perlite are also used as growing substrates, but on a smaller scale.
One of the main reasons why growers first started to use substrates is hygiene. The various diseases and viruses that may occur in the soil restrict the possibility of maximum production. Some countries moreover don’t have the means or money to adequately disinfect the soil. This has led to a tremendous increase in the annual use of new substrates or the disinfection of used substrates, ensuring better hygiene and greater uniformity of the plants and enabling more specific, and more effective control.
Control of the root environment
The great advantage of growing crops in the currently available substrates is that conditions in the rooting medium can be perfectly controlled. Growers can adjust the substrate’s water content and acidity (pH) and the composition and concentration (EC) of their nutrient solutions almost any time they find that necessary. In greenhouses, the temperature of the rooting environment can also be adjusted as required. Water content and EC are particularly important control instruments, which growers can use to give their crops a generative or vegetative impulse to promote either flowering and fruit set or the development of the foliage. Conditions in substrates can moreover be far more quickly adjusted to respond to changes in a crop’s surroundings, such as a sudden change in weather.
Over the years, the range of substrates has become quite diverse, with different substrates for different crops and different cultivation strategies. They vary from relatively dry, promoting generative growth, to relatively moist, boosting vegetative development. And they also differ in terms of the available rooting volume, their period of use or stability – with some retaining their structure for less than one year and others for several years – and their resaturation capacity. All this combined with the greater expertise and experience that have been obtained over the years, and the more efficient irrigation technology has led to further growth of the already impressive increases in production that were realised with the stonewool slabs of the first generations. Crops that are several dozen percent larger than those grown in soil are now the rule rather than the exception.
Soilless cultivation is subject to certain prerequisites, first and foremost being the availability of sufficient water of good quality. The volume available for the roots to penetrate is smaller in a substrate than in soil. The volume of available water is also smaller, making it absolutely essential to water a crop several times a day, especially in the case of fully developed crops in warm, growth-promoting conditions. What’s more, stonewool and coco slabs are less forgiving with respect to undesired salts and microorganisms, which are often largely bound, neutralised or made harmless by antagonists in natural soil. That’s impossible or far more difficult in alternative substrates.
Read more in the latest issue of The Partnership