Specifics of fertilizer application in greenhouse operations

The efficiency of vegetable cultivation in a greenhouse directly depends on the correct use of mineral fertilizers. In greenhouse conditions, calculation errors and non-compliance with the compatibility rules of chemicals can lead to harvest losses or the accumulation of harmful substances in produce. Basic nitrogen, phosphorus, and potassium fertilizers require a systematic approach to application.

The nitrogen group (ammonium nitrate, urea, ammonium sulfate, calcium nitrate, and sodium nitrate) is mainly applied before sowing or during the active growth period of vegetable crops. Urea (carbamide) is optimally suited for foliar top dressing. It is important to consider that ammonium nitrate acidifies the soil; therefore, on acidic greenhouse soils, it is advisable to replace it with sodium nitrate.

Phosphorus fertilizers are represented by superphosphate and phosphate rock. Superphosphate is applied to the soil both in autumn and spring, while poorly soluble phosphate rock — strictly during autumn tillage. Phosphorus does not have a depressing effect on plants even at high doses; however, over time, it converts into poorly soluble compounds. To avoid this, it is recommended to apply phosphorus fertilizers together with organic matter.

Among potassium fertilizers (potassium sulfate, potassium chloride, potash salt), potassium sulfate is considered the best for greenhouses, as it does not contain chlorine. It is used for autumn digging and as root top dressing throughout the growing season. Potassium chloride and potash salt are incorporated only in autumn. Out of all vegetable crops, only celery and spinach react positively to chlorides; most other plants are sensitive to them.

• Fertilizer incorporation depth — 20–22 cm
• Potassium incorporation depth in poor soils — 18–20 cm
• Granulated superphosphate application rate — half the standard amount
• Frequency of soil liming — once every 3–4 years

Soil deacidification, component compatibility, and micronutrient fertilizers

Liming reduces soil acidity and helps convert the nutrients it contains into a form available to plants. The dosage is adjusted according to the soil type: for slightly acidic or light soils, the application rate is reduced, while for heavy clay soils, it is increased. For rapid acidity reduction, the plot can be drenched with lime water (1 part limestone to 8–10 parts water) one or two days before sowing.

Liming is carried out once every three to four years. The procedure is mandatory for beds intended for beet, bean, spinach, onion, pea, and cabbage. Before application, any mineral fertilizers and lime must be thoroughly crushed and evenly spread over the entire area of the greenhouse.

When mixing fertilizers, it is important to consider their chemical compatibility; otherwise, the nutrients will convert into an unavailable form or volatilize.

It is strictly prohibited to mix:

• ammonium sulfate, nitrophoska, and ammonium nitrate — with lime, ash, manure, and poultry manure;
• superphosphates and phosphate rock — with lime and ash.

Mix immediately before application to the soil:

• ammonium sulfate, nitrophoska, and ammonium nitrate — with superphosphates and phosphate rock;
• potassium fertilizers — with phosphorus fertilizers.

Micronutrient fertilizers (manganese, copper, zinc, boron) contain elements that are required by plants in negligible quantities but prevent the development of specific diseases. Before application, the preparations are dissolved in water. The dosage is selected individually depending on the crop, soil type, and climate. Boron is of particular importance: it increases the starch content in potato tubers, sugar in tomato fruits, and also raises the levels of vitamins A and C in plants.