Phosphate fertilisers: what you need to know for effective application

17.06.2025 · Valerii Korolko · 12 min read

For many years now, our company has been working productively with the Belgian company Prayon, which specialises in the production of mineral fertilisers, in particular phosphate ones, so we would like to share our experience and practical advice on the effective use of our phosphate fertilisers.

What phosphate fertilisers are and why they matter for plants

Phosphate fertilisers – are mineral products containing phosphorus (P), an element available to plants.

Prayon's product range includes several high-quality phosphate fertilisers distinguished by high purity and consistency. Among them are various forms of phosphates (monocalcium, monopotassium, etc.), as well as soluble forms of phosphorus salts. Our phosphate fertilisers belong to such types of fertilisers as superphosphate (monocalcium phosphate), monoammonium phosphate (MAP), potassium dihydrogen phosphates (MKP) and others.

In general, the key functions of phosphorus in plants are:

1. Root development: stimulates the formation of a strong, branched root system, which improves the uptake of water and other nutrients from the soil. Strong roots are the key to a plant's resistance to stress.
2. Energy processes: phosphate groups are part of ATP, the universal "energy carrier" of cells. Without a sufficient amount of ATP, photosynthesis, respiration and other metabolic processes are impossible.
3. Flowering and fruiting: indispensable for the formation of the plant's reproductive organs: flowers, seeds and fruits. A sufficient level of phosphorus promotes intensive flowering, normal fruit set and better fruit quality.
4. Improved stress resistance: plants with an optimal phosphorus content better withstand drought, low temperatures and other stress factors.
5. Ripening: Phosphorus speeds up the ripening of the crop and improves its quality characteristics.

Thus, phosphate fertilisers are not just an "extra" but a fundamental element of the nutrition system, without which it is impossible to achieve high and good-quality yields.

Types of phosphate fertilisers: an overview of the most popular

What phosphate fertilisers are there?

Types of phosphate fertilisers are divided according to several criteria: water solubility, the origin of the phosphate rock raw material, the form of the anion (phosphate, pyrophosphate), and the phosphorus content (water-soluble and total):

Simple phosphate fertilisers (mineral):

• Single superphosphate (Single Super Phosphate, SSP). Obtained by reacting phosphate rock with sulphuric acid. Contains about 14–20 % water-soluble P₂O₅ and 46 % total P₂O₅. Besides phosphorus, it is a source of calcium and sulphur. It is often used as a basic fertiliser for ploughing or cultivation. Its drawback is a high gypsum content (CaSO₄∙2H₂O), which increases the application volume.
• Double superphosphate (Double Super Phosphate, DSP). More concentrated, with about 40 % water-soluble P₂O₅ (high bioavailability of phosphorus). Obtained by reacting ground phosphate rock with phosphoric acid. It contains less gypsum, but production costs are higher. Ideal for all types of soil and crops.

Complex (two-component) phosphate fertilisers:

• Monoammonium phosphate (MAP) (NH₄H₂PO₄). Contains 12 % N and 61 % water-soluble P₂O₅. Dissolves quickly in the soil, helping to supply plants with phosphorus promptly. Stable in storage, but may cause local acidification of the soil.
• Dicalcium phosphate (DCP) – calcium phosphate dihydrate (CaHPO₄∙2H₂O). Usually contains approximately 18 % water-soluble P₂O₅. It dissolves more slowly and is suitable for soils with a neutral reaction.
• Potassium dihydrogen phosphate (MKP) (KH₂PO₄). A universal product: contains 34 % K₂O and 52 % water-soluble P₂O₅. Ideal for foliar feeding and drip irrigation. The production of MKP at Prayon is characterised by high purity and the absence of metal impurities.

Organo-mineral phosphate fertilisers: granulated mixtures of phosphates with organic components (composts, bioactivators). They provide long-term solubility and improve soil structure.

Prayon products are predominantly mineral, but we recommend organo-mineral mixtures in the case of depleted soils.

Phosphate rock flour: 30–34 % P₂O₅, water-soluble – 0…2 %. Its use is effective in acidic soils (pH 5.5–6.5), where the solubility of phosphates increases. In moderately alkaline or alkaline soils, this form has practically no effect. Its effect may become noticeable only several years after application.

Thus, the classification of phosphate fertilisers depends on solubility, the form of P (phosphates, polyphosphates) and the presence of accompanying elements (N, K, Ca). The choice of a specific type of phosphate fertiliser should take into account the chemical analysis of the soil, the crop and the plant's stage of development.

Water-soluble phosphate fertilisers: when and why to choose them

Water-soluble phosphate fertilisers make it possible to quickly supply plants with available phosphorus.

Advantages of water-soluble phosphate fertilisers:

1. Fast action: after application, P is converted into a form available to the roots, which is especially important during periods of intensive growth or in the early phases (seedlings, rosette stage).
2. Versatility of application: they can be applied to the soil during pre-sowing treatment, as well as in the form of foliar feeding or through drip irrigation.
3. Controlled dosing: precise dosing ensures even nutrition without "over-acidifying" the plants or the soil.

However, there are also some specific features:

• Risk of phosphorus fixation in soils with a high content of iron, aluminium or calcium (especially alkaline and acidic soils). Phosphate ions are quickly "locked up" in poorly soluble salts, reducing the effectiveness of timely feeding.
• The need for precise pH control when preparing the solution (pH 5.5–6.5). If the pH rises sharply, precipitation may occur in the solution.
• Higher cost per unit of phosphorus applied compared with granulated, poorly soluble forms (rock phosphate, single superphosphate).
• Possible leaching: although phosphorus is less mobile than nitrogen, a small amount of it may leach out on light soils.

When and why to choose them:

• At the early stages of plant development: when young plants still have an underdeveloped root system, quick and easy uptake of nutrients is critical for them. Water-soluble forms of phosphorus provide this "starter" impulse for the formation of strong roots.
• For foliar feeding: only water-soluble forms of phosphorus can be used for spraying the leaves, which makes it possible to quickly correct a phosphorus deficiency in the plant.
• In cold soil conditions: at low temperatures, the activity of the microorganisms that help dissolve hard-to-access forms of phosphorus decreases. Water-soluble fertilisers provide nutrition even in unfavourable conditions.
• On soils with a neutral or alkaline reaction: on such soils phosphorus tends to bind with calcium, which makes it unavailable to plants. Water-soluble fertilisers reduce the risk of this binding.
• For crops with a short growing season: the rapid supply of phosphorus allows such crops to make maximum use of it during a short growth period.
• In drip irrigation systems: water-soluble fertilisers are easily applied together with irrigation water, providing precise and even nutrition for plants.

The most common water-soluble phosphorus fertilisers from Prayon:

• Monoammonium phosphate (MAP): used for broadcast application to the soil at sowing, as well as for preparing liquid fertilisers. The urea in its composition provides additional nitrogen nutrition.
• Monopotassium phosphate (MKP): ideal for greenhouses, glasshouses, drip irrigation and foliar feeding. Thanks to its high potassium content, it promotes better fruit development and improved transportability.
• Potassium triphosphate and other polyphosphates used in complex tank mixes for foliar application.

Recommendations for use:

• Dosage: 30–50 kg P₂O₅/ha, depending directly on the type of crop and the results of soil analysis.
• Frequency: 1–2 times per feeding season (in the phases of active growth, at the beginning of flowering) or in small-dose feedings via drip irrigation.
• Preparing the solution: first dissolve the required amount of fertiliser in a small amount of water, make up to volume, mix thoroughly and use immediately. Do not leave concentrates standing for a long time, to avoid precipitation.

When to apply phosphorus fertilisers depends on the agronomic characteristics of the crop and the properties of the soil. As a rule, phosphorus has limited mobility in the soil, so it should be applied closer to the root zone before sowing or planting. The main approaches:

Pre-sowing/pre-planting application:

• For field crops, phosphorus fertilisers are applied before ploughing or cultivation, mixing them with the soil. Depending on the level of phosphorus in the soil: in deficient soils – 80–120 kg P₂O₅/ha, in sufficient ones – 40–60 kg P₂O₅/ha.
• In orchards and berry plantations, when establishing plantations, phosphorus is often applied locally near the roots in the form of mineral granules or semi-granulated mixes.

Starter feeding:

• During the emergence phase (for cereals), it is recommended to apply small doses (15–20 kg P₂O₅/ha) in the form of water-soluble phosphorus fertilisers. This promotes rapid development of the root system and increases the hardiness of young plants.

Foliar feeding:

• Particularly effective for vegetable, berry and ornamental crops in greenhouse conditions. Water-soluble phosphorus fertilisers (MKP, MAP) are used at a concentration of 0.3–0.5%. 2–3 treatments are carried out per season (at the beginning of flowering, during fruit formation) to stimulate fertilisation and improve crop quality.

Complex feeding during flowering:

• For fruit crops, mixed NPK fertilisers with an increased P content are used. It is best to spray onto the leaf in the morning hours, avoiding the sun, to reduce the risk of burns.
• For cereal crops, phosphorus feeding is applied in the tillering phase and at the beginning of heading (10–15 kg P₂O₅/ha). This promotes grain filling and increases yield.

Spring application (for spring-sown fields):

• In conditions of unstable spring drought, it is advisable to combine phosphorus fertilisers with deep ploughing in late autumn or early spring. In this case we recommend using fertilisers that are more resistant to phosphorus fixation (DSP, DCP).

It is important to bear in mind that phosphorus fertilisers belong to the types of fertilisers that are recommended to be applied in advance, before the active growth of the root system, since P is poorly mobile in the soil. If phosphorus is applied late, close to the growing season, it will be harder for the plant to absorb it.

When applying phosphorus fertilisers, mistakes are often made that reduce the effectiveness even of a high-quality product:

Ignoring agrochemical soil analysis.

• • Mistake: standard doses of phosphorus are applied "blindly", without prior soil analysis, regardless of the actual needs of the soil and the crop.
  • How to avoid it: first carry out a full soil analysis for the content of mobile forms of phosphorus, pH, and iron/aluminium and calcium oxides. Determine the application rate (P₂O₅/ha) on the basis of the results.

Choosing the wrong form of phosphorus fertiliser.

• • Mistake: using rock phosphate or anhydrous forms on strongly alkaline or acidic soils, where they will be of little effect because of fixation.
  • How to avoid it: for acidic soils it is better to choose granulated water-soluble forms (MAP, DSP), which ensure quick uptake. For alkaline soils, lean towards products with a neutral pH (DCP, MKP).

High concentrations during foliar feeding.

• • Mistake: preparing a solution with an excessive concentration of P, which leads to leaf burns and undesirable chemical reactions.
  • How to avoid it: strictly observe the recommended concentrations (0.3–0.5% for MKP) and apply in the morning/evening hours to avoid direct sunlight.

Mixing with insoluble forms without balancing pH.

• • Mistake: combining single superphosphate with alkaline components without taking the reaction into account. As a result, phosphorus is fixed in insoluble forms.
  • How to avoid it: if the pH needs to be adjusted at the same time, apply calcium carbonate separately or use calcined forms, and minimise interaction with other reagents without prior calculation.

Failing to supply other nutrients at the same time.

• • Mistake: giving only phosphorus while ignoring nitrogen, potassium and micronutrients. Phosphorus is not absorbed without a sufficient amount of other macro- or micronutrients.
  • How to avoid it: use complex NPK fertilisers or tank mixes with a balance of macro- and micronutrients.

Phosphorus fertilisers are an indispensable component of a modern fertilisation system, providing plants with one of the key macronutrients. The Prayon range is characterised by the following advantages:

• High quality and uniformity of products: our phosphorus fertilisers undergo multi-stage control, which guarantees dosing accuracy and effectiveness.
• Wide range: Prayon offers various types of phosphorus fertilisers – from simple superphosphates to highly concentrated water-soluble forms (MAP, MKP).
• Innovative production approaches: constant improvement of processes (DA-HF, Hemihydrate, Hemi-Dihydrate, etc.) ensures high purity and minimal heavy metal impurities.
• Local service organisation: production sites in Europe and the USA make it possible to deliver products quickly to customers in different regions.

However, along with the advantages, some nuances should also be taken into account:

• Higher cost of water-soluble phosphorus fertilisers compared with poorly soluble forms.
• The need for precise maintenance of equipment (for preparing solutions and for drip irrigation) and constant pH control.
• Risk of phosphorus fixation if the wrong form is chosen for a particular soil.

To use Prayon phosphorus fertilisers effectively, you should follow these recommendations:

1. Be sure to take into account the agrochemical soil analysis and the characteristics of the crop.
2. Choose the most suitable type of fertiliser depending on the growth phase and growing conditions.
3. Use the correct application technology, taking into account the depth and placement zone in the soil.
4. Combine phosphorus application with other macro- and micronutrients for balanced plant nutrition.
5. Avoid typical mistakes (fixation in the soil, local leaf burns, uneven spreading of granules, etc.).

Thus, understanding the specifics of what phosphorus fertilisers are is the basis for planning agricultural technology. Treat phosphorus as an investment in the development of the root system and in increased yield. A correct classification of phosphorus fertilisers and following the recommendations on when to apply phosphorus fertilisers will allow you to make the most of the potential of Prayon products and obtain stable, high-quality harvests.

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