The use of artificial substrates and hydroponic systems in protected soil

An alternative to combating soil-borne pathogens is the use of media other than soil as a root-inhabiting environment, known to be free from pathogens and pests. A wide variety of media are suitable for this, including gravel, straw, peat, mineral wool, and liquid nutrient solutions. The initial variants, collectively called hydroponics, in which nutrient solutions were pressurized through gravel in special trays, proved insufficiently effective, primarily due to issues related to the nutritional regime. Cultivating cucumbers on straw bales became widely used. This method both facilitated pest control and possessed other advantages. In particular, during the microbiological decomposition of straw, the root environment warms up and the greenhouse air is enriched with carbon dioxide. Attempts to isolate straw bales from the greenhouse soil, for example, using polyethylene film, were generally unsuccessful, as this complicated the maintenance of the nutrient and water regime for the plants.

For a number of crops (tomato, carnation, lettuce), lowland peat filled into polyethylene bags is successfully used, as it is free from pathogens. The bags are usually placed on a sheet of polyethylene film that completely covers the greenhouse soil. The method of growing tomato and lettuce in nutrient film technique (NFT) has proven very productive. Under this technology, the main nutrient solution flows through a thin plastic tray and completely covers the plant root system.

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In the NFT system, constant circulation of the solution occurs, along with monitoring of nutrient content, medium pH, and solution flow, with all parameters adjusted as necessary. It might seem that plants in the NFT system would be particularly susceptible to diseases, but practice proves otherwise. Controlling water-borne pathogens (Pythium, Phytophthora) is relatively easy; only diseases such as lettuce big vein virus lettuce and powdery scab caused by the fungi Olpidium brassicae and Spongospora subterranea reach epidemic levels. The first pathogen — the vector of the big vein virus — is particularly difficult to eradicate when growing lettuce using NFT. S. subterranea causes powdery scab on the roots of tomato (and, of course, on potatoes) and is simultaneously a vector for the potato mop-top virus, although it has not yet been detected on the tomato crop.

Growing cucumbers in the NFT system proved less productive, but the crop yields well on mineral wool slabs. Cucumber seedlings are grown in mineral wool cubes, then placed on slabs, in which humidity and nutrient content are maintained via irrigation.

Using the nutrient film technique and mineral wool allows avoiding the infestation of greenhouse crops почвоо с, и а, Ее. Ч с ь 7% бы - озна: м за к. 4 Б.ч т м Х К к м: Зе Е З с к а ми # “. мы. 2 ыы < 22 И». Е. И. Ж6у # т. ‹ | а 225 Мы Миона ииди ищи ь и..... а Fig. 5.11. Various methods of growing greenhouse crops without soil:

a — peat pots; b — bags with peat; c — cucumbers in mineral wool cubes placed on mineral wool slabs; d — roots of a tomato grown in a thin-layer nutrient solution (NFT method).

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Fig. 5.12. Isolated raised beds for carnation cultivation.

soil-borne pathogens, but only if phytosanitary standards are maintained at a high level, protecting against the introduction of pathogens from the outside and the risk associated with the development of epiphytotics. Both systems require extensive practical experience to implement, as the supply of water and nutrients to plants must be precise and constant. Errors in technology are possible in both cases, primarily due to violations of the water and nutrient regime or the application of excessive fertilizer doses. Currently, the control of all environmental factors is carried out using computers. In the case of closed-loop substrate culture, some fungicides can also be used; this is discussed in more detail in Chapter 6.

Another method of controlling soil-borne pathogens is the use of isolated beds. In this case, the root zone environment consists of soil or peat in concrete troughs, which ensures isolation from the underlying ground. Polyethylene troughs are more economical, but it is quite difficult to treat and disinfect the peat or soil between two crops without damaging the polyethylene.

Isolated beds: protection against vascular wilt

Isolated beds help effectively combat dangerous root infections in greenhouses. Previously, this technology was used extensively in carnation cultivation, especially in nurseries. In such operations, vascular wilts pose the greatest threat to plants, so isolating the root system becomes the primary method of protecting plantings.

After the harvest of each crop, the substrate must be thermally disinfected. This is done by steaming, which quickly clears the beds of accumulated infection. The procedure is performed using the following methods:

• through metal grids mounted exactly to the size of the beds;
• by injecting steam under a film cover.

Despite the reliability of the method, isolated beds have not found wide application for vegetable crops. This technology is practically not used in tomato and cucumber cultivation. In commercial greenhouses, the more practical "peat bag" method is preferred for these crops.