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7 years ago

The Partnership no. 9

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  • Crops

The Ins

The Ins Outs of substrates Substrates A large part of today’s high-tech cultivation of food crops takes place in substrates such as stonewool and coco slabs. The use of substrates is also intensifying in less capital-intensive production systems. That’s not surprising, because crops can produce more, in a sustainable manner, in a rooting medium in which conditions can be effectively controlled. 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. Especially stonewool 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 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. & Hygiene 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 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. Water 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. Technical facilities Growing crops in substrates calls for a fairly extensive technical infrastructure, with all the investments and maintenance that implies. Although the precise details and dimensions may vary per system and supplier, modern substrate systems are generally accompanied by the following basic facilities: measuring or weighing systems for monitoring the slabs’ water content and the drainage percentage, an accurate trickle irrigation system, filters, a device for disinfecting the drainage water, storage tanks for contaminated and clean water, dosage units for the nutrient solutions and for acid and alkaline solutions to keep the irrigation water at the desired EC and pH, and a process computer with which the entire irrigation system can be remotely monitored and controlled. Needless to say, such systems imply a substantial investment. As high-quality cultivation systems with modern, heated greenhouses, climate computers, etc. become ever more common all over the world and growers’ capital intensities increase, the decision to switch to substrate cultivation will become easier and easier. And so substrate cultivation is becoming increasingly common also outside northwest Europe and North America. Sustainable option There’s another aspect that makes substrate cultivation interesting, an aspect that is also becoming ever more important worldwide: the environmental aspect. It has been found that substrate crops make extremely efficient use of both water and fertilisers. In principle, they are always given a surplus amount of nutrient solution, to refresh the solution contained in the slab and keep the nutrient balance in the roots’ environment at the required level. That surplus is drained from the substrate and transported to a container. After it has been disinfected, which can be realised with several methods, the water containing the nutrients can be recycled. By way of comparison: about 300 litres of water is needed to harvest one kilo of tomatoes from a crop grown in soil; this is only 10 to 15 litres in the case of crops grown in substrates in standard greenhouses, while the most modern farms with optimum irrigation and climate control consume less than 5 litres of water per kilo of tomatoes. It’s a sad fact that freshwater of good quality is becoming a scarce commodity, and that agriculture and horticulture all over the world are ever more suffering the adverse consequences of salinization. So it wouldn’t be surprising to see more and more crops being grown in substrates in the years to come. The combination of high production with extremely efficient use of resources – water, fertilisers, energy – per square metre makes this a sustainable option. Recycling waste To facilitate this envisaged growth, growers and substrate producers will have to find solutions to the waste flows that the substrate crops may generate. Spent coir pith can usually be mixed with agricultural soil as organic matter without any problems, and will then even provide a final positive contribution to the soil’s fertility. Stonewool and the plastic surrounding propagation blocks and substrate slabs should preferably be collected and recycled. This is already being done with success in western Europe and North America; other regions may have to pay more attention to this matter in the future. Technology Product 32 | The Partnership The Partnership | 33

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