Formulation and preparation of nutrient soil mixtures for flower crops

Soil, used for planting floral crops, has no natural equivalent as it is formulated artificially. Its properties are largely inherited from the natural soils of the given region. In central and northern regions, these are podzolic, slightly acidic soils or peat; in the south, various types of chernozems and chestnut soils with their inherent neutral or slightly alkaline reaction; in the arid zone of serozems, they are low-humus carbonate soils.

When formulating soil mixtures, it is taken into account that they must possess high soil fertility, as well as favorable physical and chemical properties, such as water and air capacity. A lack of oxygen in heavy loamy soil slows down plant growth and creates a deficit of nutrients. In loose, structured soil, plants suffer less from both a lack and an excess of salts. Soil must have a high absorption capacity and buffering to retain a large amount of mineral salts and gradually release them to the plants. It is very important to preserve these mentioned properties for a long time, as a large number of floral crops are perennials and grow in this soil for a long time without replacement.

Regarding organic matter content, soil is classified as: up to 10% – low, up to 30% – reduced, 30–60% – medium, over 60% – high; by density, they are divided into loose – 0.1–0.4 g/cm3, medium – 0.5–0.7, compacted – 0.8–1.0, and dense – over 1 g/cm3. For normal plant development, the amount of air in the soil should be at least 15–20%, and the total porosity – 50–60%.

In accordance with the biological characteristics of individual crops, to increase nutritional value and improve structure, substrates are formulated from four types of soil: sod, humus, leaf, and peat. Having these types of soil and sand allows one to grow any floral plants.

Sod soil should have a small-clod structure, be well-permeable to water and air, and contain a significant reserve of nutrients. It is harvested in areas with good grass-clover cover, clay, or loamy soil. Sod soil must not be taken from waterlogged areas or acidic podzols. The development of sedge, horsetails, and sorrel indicates an acidic soil reaction. If sod soil contains little clay and a lot of sand, it is useful to add a little loose, frozen, or calcined clay. Conversely, overly clayey soil is improved with sand.

Sod is cut at the end of summer or early autumn with a plough or spade into layers 30 x 30 cm and 10 cm thick. Some plants require a lighter soil with a small amount of clay but containing plenty of humus and roots. The sod layer in this case should be from 6 to 8 cm. For clay-sod soil, the sod is cut with clay subsoil up to 15–20 cm, but no deeper. The cut sod is stacked in piles layer by layer "grass to grass". The length of the pile is arbitrary, the width is up to 150 cm, and the height is 100–150 cm. Manure and lime are placed between the sod layers; this accelerates decomposition and enriches the soil with nitrogen. A groove is made on top of the pile for drainage. During the summer, the piles are mixed at least twice with bulldozers and watered to accelerate the decomposition of the sod. In the second year, mixing continues, and by the autumn of the second year, the soil is ready. In autumn, the sod soil is moved to storage facilities: it cannot be left under the open sky for a second year, as the roots rot, the soil loses its porosity, and becomes structureless. Before use, the sod soil is sieved through a screen with holes 3–4 cm in diameter so that clods the size of a pea, but no larger than a hazelnut, remain. When transplanting container plants, the clods can be larger.

Sod soil is heavy: its density ranges from 1.2 to 1.5 t/m3. It can be used for two–three years, then it becomes unsuitable for planting. Sod soil as a base for mixtures is used for pot culture of annuals – carnations, stocks, pelargoniums, and for rooting cuttings that would rot in humus soil, as well as for citrus trees and palms.

Humus soil is obtained from decomposed greenhouse manure, which is stacked in the autumn, like sod, and mixed several times during the summer season. After final decomposition, the humus soil is used in formulating soil mixtures. Manure humus is loose, light, and rich in nutrients, which promotes good growth of floral crops. Depending on the type of manure, humus soil can be heavy or light (horse manure). Its density ranges from 0.5 to 0.8 t/m3. Humus soil is not used in its pure form.

Peat soil consists of poorly decomposed plant residues. It is harvested from high-moor and low-moor peat bogs and peat crumbs. Peat is stored in stacks 40–60 cm high mixed with manure and lime, and prepared over two years by periodically turning it over and irrigating with liquid manure. Manure and lime increase the nutrient content of the peat soil, and the acidity of the peat decreases during the preparation process. This soil has a low density of 0.4–0.6 t/m3.

Peat soil is capable of absorbing large amounts of moisture, therefore it improves the water-air properties of soil with heavy particle-size distribution; it is used mixed with sand for the planting of cuttings; it is required for the culture of azaleas, camellias, and hydrangeas, and is good for the sowing of small seeds; it is added to turf soil for the purpose of enrichment with organic substances. Peat soil should not be allowed to dry out, as it absorbs water slowly. During storage, peat soil must be kept moist at all times.

Preparation and use of leaf mould

Leaf mould is obtained from the fallen leaves of linden, hazel, maple, elm, poplar, apple, and pear trees. Oak and willow leaves contain tannins, so they are unsuitable for producing leaf mould. This is a light soil with a density of 0.4–0.6 t/m3.

The substrate preparation technology includes the following stages:

• Leaves are raked into piles in the autumn or spring.
• As they decompose and settle, they are placed in stacks, where they mineralize over two years.
• While the leaves lie loosely, they are compacted and irrigated so that microbiological processes proceed faster.
• In the second year, they are turned over two or three times and irrigated with liquid manure, which introduces bacteria that accelerate the rotting of the leaves.
• As leaves decompose in the soil, acids accumulate, which inhibit the further decay of the mass. The harmful effect of acidity is eliminated by adding slaked lime to the stack during turning at a rate of 0.5 kg per 1 m3 of undecomposed leaves.

Leaf mould is used for sowing seeds in boxes; in mixtures with peat and sand (2:3:1 or 2:4:1) — as a base for mixtures for primula, cyclamen, anthurium, begonia, and cineraria.

Classification of soil mixtures and acidity

All types of ready-made garden soil are stored in special soil storage facilities. As needed, the required mixture is prepared from them, which, depending on the ratio of components, can be heavy, medium, or light:

• A heavy soil mixture contains, by volume, three parts of turf soil, one part of humus or leaf mould, and one part of sand.
• A medium soil mixture contains two parts of turf soil and humus (leaf mould) and one part of sand.
• A light soil mixture contains one part of turf soil, three parts of humus (leaf mould) and one part of sand.

Soil reaction is also of great importance for the growth and development of flower crops, as the availability of mineral nutrients and the degree of their absorption by plants depend on it. Optimal pH values for floral plants are shown in Table 210 (Sheudzhen A.Kh., Kotlyarov N.S., Kurkaev V.T. et al., 2004).

Table 210 – Optimal soil reaction value for floral plants

Methods for determining the acidity of greenhouse substrates

Substrate acidity is determined by the content of free or exchangeable hydrogen ions. In limed neutral substrates saturated with calcium, mobile hydrogen is almost absent, and there are no large differences in analysis results between aqueous and salt extracts.

Therefore, in neutralized substrates, acidity can be determined in both salt and aqueous extracts, while in raw materials for formulating soil mixtures, acidity (pH) is determined in a 1 N KCl solution, taking into account the quantity of exchangeable hydrogen ions. When determining acidity in an aqueous extract, only the content of free hydrogen ions is taken into account. Therefore, salt-based acidity is always higher than water-based acidity.

Substrate acidity is influenced by water hardness and the acidifying effect of fertilizers. Depending on the pHKCl value, a greenhouse substrate can be: acidic, neutral, or alkaline.

Regulation of soil acidity levels

To reduce soil acidity, liming is performed and physiologically alkaline fertilizers are used.

If acidification of the substrate is necessary:

• add acidic sphagnum peat;
• apply physiologically acidic mineral fertilizers;
• or add acids to the irrigation water.

Repeat liming of soils after 8–10 years when acidity rises again.