Hydroponics and modern vegetable growing technologies on substrates

Hydroponics attracts vegetable growers due to its high production culture, the ability to fully automate nutrient supply, and a reduction in manual labor costs. This method is particularly promising where there are no cultivated soils. However, the technology requires strict discipline and high qualification from an agronomist.

Substrate selection and the transition to low-volume technology

Among hydroponic methods (water culture, aeroponics, and aggregate-ponics), aggregate-ponics is the most common in practice. It involves growing plants on solid granular substrates with low water capacity and periodic wetting of the roots with a nutrient solution. Substrates must be inert, durable, and possess good thermal and water-air properties. Gravel, crushed stone, expanded clay, perlite, or vermiculite are used for this purpose.

When choosing gravel and crushed stone as a substrate, consider the following physical parameters:

• Gravel particle size — 3–5 mm
• Crushed stone particle size — 5–25 mm
• Carbonate content — no more than 20%
• Bulk density — 1.5–1.7 g/cm³
• Water-holding capacity — 9–10%

The material is poured in a 25 cm layer into reinforced concrete basins. The service life of such a substrate is virtually unlimited if maintenance rules are followed:

1. Periodically wash the substrate with clean water.
2. Acidify the working environment to pH 5.6.
3. Perform disinfection with a 5% formalin solution.

In modern vegetable production, it is recognized as economically beneficial to grow plants in individual low-volume units rather than in continuous trays. For this, polyethylene containers with a volume of 3–17 liters (which accommodate 1 to 4 plants) or gutters with internal plastic lining are used. A fully soluble nutrient solution is supplied via drippers, overhead irrigation, or by the sub-irrigation method from a basin. The technology of low-volume hydroponics is successfully applied not only for vegetables but also for growing roses.

For low-volume substrates, both inert materials (mineral wool, perlite, vermiculite, gravel, volcanic slag) and organic soil substitutes (peat moss, sawdust, wood bark, coconut fiber) are used. The most widespread is low-volume hydroponics on mineral wool with drip irrigation. This sterile substrate is obtained by melting diabase at temperatures exceeding 1600 °C. It does not contain nutrients, has a pH of about 7, is similar in properties to peat moss, but differs from it by its lower weight.

Mineral nutrition, diagnostics, and top dressing recipes

To prepare nutrient solutions in protected ground, potassium, ammonium, and calcium nitrates, urea, double superphosphate, potassium sulfate, and potassium magnesium are used. Among complex fertilizers, ammophoska, carboammophoska, and nitroammophoska are employed. Of particular value for hydroponics are fully water-soluble complex compounds without ballast impurities.

The plant's need for nutrition is determined by the results of chemical analysis of the substrate and the plants themselves, as well as by visual diagnostics. Analysis of the substrate and plant tissues is the primary method, as it allows for an accurate assessment of the nutrient supply for the plantings over a long period.

For prompt adjustment of cucumber and tomato nutrition, foliar top dressing is applied. The consumption of macro-fertilizers for preparing the working solution is indicated in the table:

A solution of trace elements is also added to the tank mixture. The concentration of active ingredients in the working solution should be:

• boric acid — 0.03%;
• iron citrate — 0.04%;
• magnesium sulfate, zinc, copper, cobalt, ammonium molybdate — 0.005% of each substance;
• potassium iodide — 0.001%.

To precisely manage the productivity of vegetable crops in protected and open ground, it is necessary to regularly conduct agrochemical analysis of the soil. During the growing season, it is important to timely identify hidden nutrient deficiencies. This can be done visually by the characteristic changes in the leaf blade and stems:

• Nitrogen: the lower leaves take on a pale green color, the apical leaves yellow and die off. The leaf blades are small, and the stem becomes thin and brittle.
• Phosphorus: leaves turn dark green or bluish with a reddish-purple tint. Plant growth slows down, leaf die-off accelerates followed by blackening, and flowering and ripening are delayed.
• Potassium: yellowing and tissue death (marginal necrosis) are observed, leaf edges curl downwards, and internode growth stops.
• Magnesium: lightening of leaves occurs with a color change to yellow, red, or violet, and interveinal chlorosis develops while the veins remain green.
• Calcium: necrosis of leaf edges, apical buds, and the root system develops.
• Iron: uniform interveinal chlorosis appears, leaves turn pale green or yellow without tissue death.
• Boron: apical buds, roots, and leaves die off, and mass shedding of fruit set occurs.

Regulations for fertilizer application and preparation of working solutions

Localized fertilizer application during seed sowing and transplant planting is the most efficient method of use. In this case, application rates are reduced several times over, while the impact on yield remains practically the same as with broadcast application. The main technological requirement is to prevent direct contact between the granules and the seed material.

1. Apply mineral fertilizers to the row zone.
2. Thoroughly mix the applied fertilizers with the soil.
3. Cover with a 5–7 cm thick layer of soil.
4. Sow the seed in the prepared row.

When planting cabbage transplants, tomatoes, peppers, and eggplants, nutrients are placed directly into the planting hole. For a balanced start, use a mixture of humus and nitroammophoska. If there are no precise dosage recommendations for a specific crop, the agronomist should refer to basic average application rates.

• Basic application rate of nitroammophoska per soil area — 1 matchbox per 1 m²
• Dosage of nitroammophoska per planting hole — 1 teaspoon
• Dosage of humus per planting hole — 1–2 handfuls

If a deficiency of a specific nutrient is detected, for example, nitrogen, apply it together with phosphorus and potassium in reduced dosages. These elements act as synergists and significantly enhance the effect of nitrogen. The plant demand for nitrogen nutrition increases sharply after heavy rainfall and prolonged cold spells.

Foliar treatments with macro- and micronutrients serve as "first aid" to support vegetative tone, especially during a sudden transition from prolonged cloudy weather to clear weather. Adding urea to the working solution improves leaf wettability and accelerates the absorption of other nutrient compounds. For a comprehensive effect, alternate mineral top dressing with organic ones — cow manure, poultry manure, or fermented plant residues.