Technological features of seedling production for low-volume hydroponics

Most greenhouse complexes have switched to low-volume cultivation technology for vegetables. The success of this method depends entirely on the quality of seedlings. Its main feature is the preparation of the root system for development in a very limited volume of substrate with a high concentration of salts. The traditional approach will not work here.

During standard cultivation on peat, plants are irrigated with clean water, as the initial supply of fertilizer is sufficient for the entire period, and the salt concentration decreases by the time of transplanting. For low-volume hydroponics, the strategy is changed: the salt level during the seedling period is gradually increased. This prevents salt stress when young plants are moved into the dense nutrient solution of the artificial substrate.

• Target soil EC during traditional transplanting — no more than 1.2–1.4 mS/cm
• Share of loosening agents in peat substrate — 30–50 %
• Initial EC of peat extract — 1.0–1.2 mS/cm
• Seedling reserve for "double" cubes — 12 %

Preparation of the nursery section and peat substrate

If there are no tables in the nursery section, the leveling of the site must be perfect. The soil is thoroughly planned, rolled, and covered with light-proof film, onto which the containers are then placed. The slightest slope will cause the nutrient solution to drain. As a result, some plants will suffer from overwatering and moisture stagnation, while others will suffer from drying out.

To prepare the peat substrate, peat moss is taken and loosening agents are added to it: perlite, fine expanded clay, vermiculite, or sawdust. Loose materials make the mixture light and porous, improving air access to the roots. Before use, the substrate is enriched with fertilizers so that the extract EC is 1.0–1.2 mS/cm (the EC of a water extract will be 1.75 times lower). Seedling pots are filled strictly identically, leveling the peat along the upper rim.

To obtain uniform seedlings with a powerful root system, the agronomist needs to control three factors:

• quality selection of the substrate;
• uniform filling of the pots;
• even distribution of the nutrient solution across the containers.

Specifics of cultivation on mineral wool

For cultivation on mineral wool, cubes of different sizes are used depending on the crop and the chosen scheme. Cucumber, eggplant, and pepper are sown directly into the cubes, while tomato is first grown in trays (using "finger" trays) and then transplanted. "Double" cubes allow saving nursery section space but complicate maintenance. Plants in them develop unevenly, so they have to be carefully sorted before transplanting into the greenhouse. In addition, some seedlings may be damaged during transport, so with this scheme, it is mandatory to grow 12 % of plants in single cubes for replacement.

An important aspect of the technology is the soaking of the cubes. The solution must soak the mineral wool completely, from bottom to top. With a moisture deficit, the central part of the cube will remain dry, which will inhibit root development. This process can be controlled by weighing.

1. Saturate several test cubes with the solution to 100% saturation and weigh them to determine the reference mass.
2. Perform complete soaking of the entire batch of cubes.
3. Selectively weigh cubes from different zones of the nursery and compare their weight with the reference.

The most important part of seedling fertilization technology is the systematic control of substrate moisture, pH, and EC indicators. Moisture should be within 60% before irrigation and 85% after irrigation is finished. Optimal moisture is achieved by using the gravimetric method. Knowing the mass of the pot at 100% saturation (determined in advance), one can calculate the mass of the cube at 60% and 85% substrate moisture (the mass of the plant itself must be taken into account).

EC and pH of the extract should be monitored daily. When growing on peat at low substrate moisture, it is difficult to take a sample. In such cases, it is recommended to use the volumetric method (add 2 parts of water to one part of substrate, stir, let it sit for half an hour, and then measure). Obtaining high quality seedlings is facilitated by establishing the dynamics of changes in these indicators and keeping them within optimal parameters, as each crop has optimal values that should be aimed for from one irrigation to the next.

The increase of EC in the substrate should be gradual, from one irrigation to the next.

Thus, a properly prepared substrate and timely and high-quality irrigation ensure the formation of transplants with a healthy and vigorous root system.

Quality of transplants. Throughout the entire growing season, it is important to monitor the development of not only the above-ground part of the plant but also the roots. In mineral wool, provided the irrigation regime is followed, a vigorous root system capable of nourishing the plant during the rooting period is generally formed. Problems arise more frequently with peat substrate, in which root development is concentrated within the soil clod, while the bulk of the roots is located around it.

If the roots do not develop inside the clod, it is necessary to urgently identify the cause. The main risk factors include:

• overwatering;
• high EC values;
• "heavy" substrate.

The irrigation regime and EC can be adjusted in time, but the problem of substrate preparation must be solved before sowing; otherwise, it is impossible to obtain high-quality transplants and, ultimately, high yield.