CLOSED GROWING SYSTEMS FOR MORE EFFICIENT AND ENVIRONMENTAL FRIENDLY PRODUCTION

To avoid emissions of fertilizers and pesticides, Dutch growers have to change over to closed soilless growing systems. During the last few years many systems have been developed and tested. Now an inventory has been made followed by an assessment of the systems to realize more sustainable systems for various glasshouse crops.

The growing systems should have a separated drain water outlet within the row to avoid or decrease mutual infection. The materials and substrates used should have a life span of at least four years and should be disinfected by steam sterilization. No materials are permitted of which the manufacture or recycling are questionable (for example a recycled material must have the same quality as the original one) or cause a major waste flow. The best choice is to use materials such as polypropene, coated steel and aluminium. The best choice for firm substrates are rockwool slabs for more than one year and polyurethane foam and, for loose substrates, clay granulates, perlite, pumice stone and "flugsand". Sometimes, rough sand or Irish peat are suitable. NFT and aeroponics supply all demands but have an increased risk of disturbances due to the small water buffer.

Investments and annual costs of growing systems may vary among different groups of crops, but comparing the annual costs of various systems for one crop, minimal differences appear, while the more sustainable systems prove to be the cheapest.