Technology of vegetable crop seedlings cultivation in trays

The transition from growing non-potted seedlings to tray technology with a closed root system is a necessary condition for modern high-tech vegetable production. Old methods with a high share of manual labor do not ensure plant uniformity and their rapid establishment. The tray method allows for full mechanization of the process, eliminates root damage during transplanting, and provides a significant advancement in crop development.

• Seedling survival in open soil — 100%
• Field planting time — 5–10 days earlier
• Advancement in plant development — 15–20 days
• Harvests per season — 2–3 per unit area

Substrate parameters and nutrients

With tray technology, traditional soil is replaced by organic, mineral, or synthetic substrates. For plastic trays, mixtures based on high-moor and transitional peat with the addition of perlite, vermiculite, agro-perlite, or fine expanded clay are considered the best. A quality substrate must be highly porous, moisture-retentive, and free of weed seeds, disease pathogens, and pests.

The choice of specific components depends on their availability and physicochemical properties. The characteristics of the most common greenhouse substrates are given in the table.

An important factor in the suitability of a substrate is the level of its initial nutrient charge. Systematic agrochemical analyses allow for the control of salt concentration, preventing their excess.

Technological process of preparation and sowing

The technology includes nearly two dozen operations, sequentially performed by machines and mechanisms. Modern greenhouse equipment allows for the automation of mixture preparation, tray filling, precision sowing, and irrigation. This eliminates manual labor in the most labor-intensive stages and guarantees uniform seeding depth depth of seed placement.

1. Analysis of peat quality for compliance with standards and phytotoxic safety.
2. Peat mixing in a shredder-mixer and its aeration.
3. Moistening and mixing the peat with mineral components (perlite or vermiculite).
4. Conveying the finished mixture to the tray filler.
5. Passing trays under a dibber marker to create a seed bed of a specified depth.

Automation of these processes ensures identical starting conditions for each seed. At the output, the farm receives uniform seedlings with high viability, fully suitable for mechanized planting in the field.

The quantitative ratio of substrate components can vary, depending on their availability and the seasonality of seedling production. In winter, when mixing Kikila peat, 50 L of perlite and 80 L of vermiculite are added to each bale (315 L). In the summer formulation, perlite is excluded, and the vermiculite content is increased to 120 L per bale. However, formulations can be quite different, depending on the availability of organic-mineral components suitable for use in the substrate.

Next, the trays, with cells densely filled with shredded, moistened, and well-mixed substrate, are moved on a chain conveyor under a DECOP pneumatic sowing machine. It is equipped with interchangeable plates that allow for sowing seeds of different anatomical structures, sizes, and weights. The sowing machine is capable of providing a sowing rate of one, two, three-to-five seeds (or more) per cell. The configuration of the sowing machine also includes several types of heads with different numbers of seed tubes, designed for working with 128, 210, and 300-cell trays.

To prevent drying out, trays with sown seeds are passed under a mulching unit for covering with a thin layer (0.5–1.0 mm) of vermiculite. Then, they pass through an irrigation tunnel, where the substrate is watered with sprays at a temperature of 35–40 °C (at a rate of 200 ml per tray) to saturate the seed embryo with moisture, and are fed by a roller conveyor to the stacking area.

Figure 5 – Components of the Conic sowing line a – peat shredder-mixer; b – tray substrate filler; c – dibber marker; d – sowing machine with seed tubes; e – mulching unit; f – irrigation tunnel.

Sowing. For sowing, regular or pelleted seeds are used; their seeding depth is selected based on their weight, size, as well as the cell parameters of the tray used. Table 20 — seeding depth of vegetable crops in polystyrene trays for seedling production (according to R. A. Gish, 2011)

Crop Tray type recommended seed embedding depth">Seed embedding depth , mm

1 2 3

128 14 Watermelon 210 —

128 12 Eggplant 210 10

128 10 Basil 210 10

128 11 Melon 210 —

128 16 Summer squash 210 —

300 — Cabbage 128 8 white-headed 210 7

128 7 Lettuce 210 6

128 5 Celery 210 5

128 8 Onion 210 8

128 14 Cucumber 210 —

128 12 Pepper 210 10

128 6 Parsley 210 6

128 6 Arugula 210 6

128 10 Tomato 210 10

128 10 Dill 210 10

Seed germination. Stacked on pallets, the trays marked with relevant information on tags (crop, cultivar, sowing date, client, dispatch date, etc.) are moved to a specialized seed germination chamber. Artificially created and maintained optimal parameters of relative humidity of air and temperature required for each crop promote uniform emergence in the shortest possible time. At the same time, the duration of the sown trays' stay in the chamber must not be less than 24 h. Table 21 — Parameters ensuring accelerated emergence in the seed germination chamber (according to R. A. Gish, 2011)

Crop Temperature, Root length, Duration of tray stay

°С mm in the chamber, days

Watermelon 22-24 15-20 2-3

Eggplant 24 3-5 2-3

Melon 22-24 10-15 1-2

Summer squash 22-23 9-12 2-3

Cabbage 20-22 1-2 1-2 white-headed

Tomato 22-24 2-4 2-3

Onion 19-21 2-3 2-3

Cucumber 22-23 10-15 2-3

Lettuce 16-18 3-5 1-2

Celery 16-18 3-5 5-6

Pepper 23-25 3-4 2-3

* Relative humidity of air">relative humidity of air 93-95 %

Upon the emergence of more than 50% of sprouted seeds, the trays are placed on racks in the greenhouse. Subsequently, the Technology of growing transplants">technology of growing transplants is similar to traditional ones, so we will note only the specific features of the new technology.

Figure 6 – General view of the transplant greenhouse

Growing technology. During the transplant period, growth processes dominate in vegetable plants; by skillfully managing them, it is possible to obtain high-quality transplants in 25-35 days instead of the 40-45 to 55-60 days recommended by traditional technology (e.g., cucurbits, solanaceous crops). The problem consists in preventing the stretching of the hypocotyl in seedlings, on the one hand, and on the other — in supporting and managing the growth processes occurring in them by optimizing growing conditions. With the non-pot method of growing transplants, to avoid stretching of the hypocotyl, recommendations from the Department of Vegetable Growing of the RSAU-MAA were resorted to, which prescribed a sharp decrease in air temperature in the cultivation facility after the emergence of seedlings. For example, for pepper, the following temperature regime was recommended: from sowing to emergence — 25-30 °С, then, for 4-7 days after emergence, a decrease in daytime temperature to 13-16 °С, and at night — to 8-10 °С. In the following days, these same recommendations prescribe maintaining a difference between night and day temperatures at the level of 10-14 °С. Such an approach in the new technology does not justify itself, as plants experience significant stress, and low temperatures hold back the growth of fragile seedlings. Moreover, it is not always possible to apply this technique in a greenhouse, since, as a rule, different crops are growing there simultaneously or plants are at different stages of development.

The technical and technological equipment of modern transplant greenhouses allows for controlling many microclimate parameters with sufficiently high precision, which enables maintaining conditions for transplant growth close to optimal, contributing to the production of high-quality planting material.

When producing transplants in a specialized cultivation facility, to stabilize the quality of the produced material, it is more justified to ensure illumination in the range of 8-9 thousand lux in the first half of the growing season of the transplants, to maintain the substrate in a moderately moistened state, and to lower the air temperature in the greenhouse after the formation of cotyledon leaves both during the day and at night to the maximum permissible values, taking into account the crop's relation to this factor. However, it should be remembered that a drop in night or day temperature below the recommended values (16-18 °С) leads to the weakening of plants, a decrease in immunity and resistance. High night temperature leads to stretching and etiolation of plants, significantly reducing their cold resistance and survival rate upon transplanting to a permanent growing site. Table 22 — Optimization of conditions for growing pepper transplants at different stages of their development at CJSC "Sad-Gigant" (according to R. A. Gish, 2011) Growing conditions Stages of transplant growing I II III IV opt.. opt.. opt.. opt.. max. max. max. max. min. min. min. min. Day temperature, °С 21 23 25 18 18-20 25 18 22-24 27 16-18 21-22 30 Night temperature, °С 21 23 25 16 17-18 — 16 19-20 — 14 14-15 — Illumination, thousand lux — 8-9 8-9 Sun-protection and energy-saving screen with an absorption capacity of 25-30% of the light flux Ventilation — Strong Moderate Moderate Relative humidity, % 92-95 60-65 60-70 60-70

* Stages of transplant development: I — sowing - seed sprouting; II — hypocotyl germination - appearance of cotyledon leaves; III — appearance of cotyledon leaves - formation of the first pair of true leaves; IV — formation of 2 true leaves - appearance of 4-5 fully unfolded leaves.

Irrigation is one of the most important elements of the technology for growing transplants. By standardizing and systematically monitoring the amount of water or nutrient solution supplied to each plant or each cell, it is possible to obtain high-quality transplants with a well-developed root system, uniform in height, with 5–6 true leaves. High uniformity of irrigation is achieved through systematic monitoring of nozzle performance on the boom and weight control of the trays.

Transplant irrigation and top dressing are carried out daily via an irrigation boom using micro-sprinkling. Two to three times a week, the plants are top-dressed with a standard solution with a pH of 6.4–6. and EC of 1.2–2.2. The remaining irrigations are performed with clean water.

During the growing season of the transplants, special attention is paid to preventive measures for disease control and suppression of pest activity, as well as adaptation to open field conditions. To this end, at the two-true-leaf stage, the transplants are sprayed with a Previcur solution (0.3%), which has a systemic fungicidal effect and helps prevent root rot in plants. At the 5–6 leaf stage, the transplants are treated with a solution of the systemic insecticide Confidor (0.3%), adding it to the nutrient solution. Such treatment prevents the transplants from being infested by sucking pests for 1.5–2.0 months. 7–10 days before transplanting, for fungal infection prevention, they are treated with the preparation "Ridomil Gold" (0.1–0.2%) and hardening begins.

Transplant age. Transplants grown in trays transplants, due to their well-developed root system and the preservation of its integrity during harvesting and planting (manual or mechanized), are suitable for planting in the open field significantly earlier than bare-root transplants.

Depending on the tray type used, the age of transplants at the time of planting for the most common crops in the south of Russia is:

20–25 days — cucumber, spinach;

30–35 days — basil, eggplant, pepper, tomato, lettuce, white cabbage, parsley, dill, zucchini, watermelon, melon;

40–45 days — onion;

60–65 days — celery.

Staged young transplants grown in trays (with correctly selected calendar dates) take root significantly faster in the open field, rooting at almost 100%. This is explained by the activation of the growth of lateral roots of the transplants, which contributes to rapid rooting of plants, minimization of post-planting stress, and better adaptation of plants to new growing season conditions.

Delivering transplants from the producer to the planting site without reducing the quality of the planting material remained a problem for a long time, as it was damaged during transport and wilted due to the lack of specialized packaging. Currently, cardboard containers of various designs have been developed, allowing transplants to be transported over distances of up to 1.5 thousand km. Shelving units are used for on-farm placement.

Figure 7 - Methods of transplant transportation: a – in a cardboard container; b – on racks

Prolonged operation of a transplant greenhouse and the cultivation of many crops belonging to different botanical families are associated with the accumulation of a large amount of fungal and bacterial infection in the growing facility. Therefore, it is standard practice to stop the production process once a year for the disinfection of the growing facility.

Preparatory work includes the following operations:

• removing equipment from the greenhouse;
• sweeping out plant residues;
• draining residues of working and stock solutions;
• washing out containers holding agrochemicals.

Then, using a 1% hot solution of the preparation Bionet, the metal structures, transparent enclosure, and the tools and equipment used in work are washed, leaving the preparation on them for a period from half an hour to a day.

Following this, the flushing of the nutrient solution supply systems begins:

1. First, the system is flushed with nitric acid (pH 1.5–2.0), leaving it for 8–12 hours.
2. Then the solution is drained and the system is flushed with water.
3. After this, the system is filled with the preparation CID-2000 (1% solution) with an exposure of 8 hours.
4. After draining the preparation, the system is flushed with clean water until the solution is completely removed.

In addition to Bionet for treating structures, transparent enclosures, and nutrient solution tanks, the preparations Ecocide (2–3%) and Kickstart (2–3%) are effective. They are low-toxic, and their effect is immediate. The preparation Virocid (1%) is very effective for these purposes; it is also low-toxic but requires an exposure of up to 7–10 days.

For the disinfection of plastic and polystyrene trays, it is recommended to soak them with subsequent rinsing in a warm 1% Virocid solution. After 1–2 days, the trays should be rinsed with warm water.