In this article you will find out why plants need phosphate, which phosphate fertilizer you can apply when and how - and why these fertilizers are problematic, especially because of their use in agriculture.
When and why should you use phosphate fertilizer?
Phosphate fertilizers are necessary for plants when there is a phosphorus deficiency that affects growth and flowering. They contain phosphorus in varying amounts and should only be used after a soil analysis. Caution: Phosphate fertilizers can contain heavy metals such as cadmium and chromium.
- There are numerous phosphate fertilizers with different levels of phosphate between 5 and 52 percent.
- They should only be used if there is proven phosphate deficiency in the soil or plants.
- Phosphate fertilizers contain heavy metals such as cadmium and chromium, which are deposited in plants, animals, soil and groundwater.
- A soil analysis must be carried out before use; the dosage can also be reduced by adding stable manure.
What is phosphate fertilizer?
Phosphorus (P), together with nitrogen (N) and potassium (K), forms the three main nutrients that are vital for the growth of plants and are therefore the most important components in every complete and NPK fertilizer. Sometimes a phosphorus deficiency can occur, which significantly affects flower and fruit formation and the he althy growth of ornamental and crop plants. In this case, a special phosphorus fertilizer can help.
Phosphate fertilizers consist of the s alts of phosphoric acid (H3PO4). Since pure phosphorus is poorly soluble in water, it must first be chemically processed before it can be used as fertilizer. Various acids break down the required calcium phosphate. Only then are the nutrients available to plants.
Composition and properties
“More uranium is mined in phosphate mining worldwide than is used in nuclear reactors.”
Raw phosphorus is mined in huge mines
The raw phosphorus required for phosphorus fertilizer is usually obtained through mining from natural deposits that have formed from the deposits of former marine animals that are millions of years old. Many of these deposits are located in the countries of North Africa as well as in South Africa, Jordan, China and Russia. Saudi Arabia is the world's largest phosphate producer. Rock phosphate is also obtained from the remains of seabirds, the so-called guano.
The plants absorb the processed phosphorus through their roots, with the fertilizer being best available at a pH value between 6 and 7. Various phosphorus foliar fertilizers are available commercially, but they only help in the short term - the lion's share of the nutrient is ultimately absorbed by the roots.
Excursus
Thomas flour - a cheap but problematic phosphate fertilizer
So-called Thomas flour is a very inexpensive phosphate fertilizer, which, however, should not be used due to its high content of the heavy metal chromium - the heavy metal accumulates in the soil and plants and also reaches the groundwater. Thomasmehl is a waste product from iron ore smelting and is therefore highly contaminated.
Effects and effects
Phosphorus is an important component of every plant cell. The element is essential for the functioning of metabolism in all ornamental and useful plants. A phosphorus deficiency, which is detected either by stunted plant growth or, more commonly, by soil analysis, should therefore be remedied immediately. The use of a phosphorus fertilizer, when applied correctly, has the following effect:
- Roots grow deeper, so the plants can be better cared for
- bud and flower formation is supported
- Support cell division and thus leaf and shoot growth
- Support resistance to diseases and pests
So that the phosphorus fertilizer can work optimally, you should use it before using it
- carry out a soil analysis
- and only apply phosphorus fertilizer if the analysis shows a deficiency
- then carry out a pH test
If the soil is too acidic (pH value below 5.5), it should first be brought to the optimal range between 6 and 6.5 by liming. If the result is more than 7, it is better to choose a water-soluble phosphate fertilizer. But be careful: phosphate fertilization not only has an effect on the plants, but also directly on the soil and groundwater. A too high proportion of phosphate in water can be recognized by excessive algae growth, and aquatic plants and aquatic creatures such as fish, snails, mussels and crabs die due to the lack of oxygen. This effect can often be observed in waters located in heavily agricultural regions. Therefore, phosphate fertilization should only be carried out if it is absolutely unavoidable.
Excursus
Caution, highly toxic
Phosphate fertilizers contain highly toxic components
Phosphate fertilizers are indispensable, especially in industrial agriculture, in order to achieve the highest possible yields. However, these fertilizers are also highly problematic because they are heavily contaminated with toxic heavy metals, especially uranium and cadmium. By using such fertilizer, these toxins inevitably end up in our food via plants and animals. There is currently no legal maximum uranium content in Germany, only a recommendation from the Federal Ministry of Food and Agriculture. Here the maximum value is 50 milligrams of uranium per kilogram of phosphate fertilizer.
Types of phosphate fertilizers
Numerous phosphorus fertilizers are commercially available specifically for home and hobby gardens. In addition to pure phosphorus fertilizers, you can also choose complex fertilizers with a high phosphorus content. Typical examples are universal or complete fertilizers as well as NPK fertilizers, because in these products the three main nutrients nitrogen, phosphorus and potassium form the most important and therefore the largest components in terms of quantity.
The following table provides you with an overview of common single- and multi-component fertilizers.
| Type of fertilizer | Phosphate content | Special features | Price |
|---|---|---|---|
| Superphosphate | 18 percent | water-soluble granules, with NPK | approx. 1.10 EUR per kilogram |
| Superphosphate with sulfur | 18 percent | Water-soluble granules, also contains sulfur | approx. 3.40 EUR per kilogram |
| Phosphate potash / Thomas potash | 8 percent | Potassium fertilizer with a high phosphorus content as well as magnesium and other trace elements | approx. 2.10 EUR per kilogram |
| Dehner phosphate potash fertilizer with long-term effect | 15 percent | PK fertilizer with magnesium and sulfur | approx. 1.30 EUR per kilogram |
| P 20 liquid phosphate fertilizer | 20 percent | Concentrate, to be diluted with water, also suitable for foliar fertilization | approx. 4 EUR per 100 milliliters |
| Phosphor Plus liquid fertilizer | 7 percent | Additional fertilizer with phosphorus and potassium for flowering plants | approx. 13.50 EUR per liter |
| Thomaskali | 8 percent | granulated PK fertilizer with magnesium | approx. 0.90 cents per kilogram |
Multi-component fertilizers that contain both phosphorus and other nutrients are usually completely sufficient for home and hobby gardens. Phosphate fertilizer with a very high phosphate content, about
- Diammonium phosphate (DAP) with 46 percent phosphate content
- Monoammonium phosphate (MAP) with 52 percent phosphate content
, on the other hand, are primarily used in agriculture. If you need a fertilizer with a high phosphate content for your home garden, it is better to choose so-called superphosphate. This contains calcium phosphate and sulfuric acid, with the phosphate content varying between 16 and 22 percent depending on the manufacturer.
Correct application
If the phosphate fertilizer is not used properly, it can have dire consequences
Phosphate fertilizer requires proper handling in order to avoid possible overdoses and thus unnecessary exposure to heavy metals. It's not just about the correct, needs-based dosage, but also the time and manner of application.
Time
When you apply phosphate fertilization depends primarily on the specific product you want to apply:
- Water-soluble phosphate fertilizers: such as. B. Superphosphate is added to the soil in spring as basic fertilizer. Choose granular fertilizers as they are released more quickly.
- Phosphate fertilizers with a high proportion of raw phosphates: are applied in autumn. They are particularly suitable for acidic soils / soils with low pH
Liquid fertilizers containing phosphates (€8.00 on Amazon) are practical because you simply add them to the irrigation water and water the plants directly. You can also use these during the growing season.
Dosage and effects
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Phosphate fertilizers should be applied as close as possible to the roots, as they only have their effect here. In contrast to nitrogen fertilization, you do not have to worry about root damage. And this is how it is fertilized:
- Please follow the manufacturer's instructions regarding dosage and application.
- The dosage also depends on the specific phosphate content of your garden soil.
- For superphosphate, around 30 to 60 milligrams of phosphate fertilizer per square meter are recommended.
- Sprinkle the phosphate fertilizer directly onto the root disc of the plant to be fertilized.
- Larger areas, such as lawns, can be fertilized evenly using a spreader.
- Work the granules in superficially.
- Water vigorously to allow the fertilizer to dissolve and seep into the soil.
Lower the dosage by applying organic fertilizer in the form of compost or manure at the same time. Manure in particular allows the amount of fertilizer to be reduced by up to 40 milligrams per square meter. When using compost you need 15 milligrams per square meter less phosphate fertilizer.
Frequently asked questions
Are there alternatives to phosphate fertilizer?
Stable manure is a great alternative to phosphate fertilizer
Yes, fertilize your garden with manure. This contains a high proportion of natural phosphate (similar to seabird dung), but it takes some getting used to for some gardeners. Make sure that poultry manure in particular must be well rotted before you spread it! Otherwise, agricultural scientists all over the world are researching to discover alternatives to mineral phosphorus fertilizers - it's about time, because the world's phosphorus deposits are gradually coming to an end.
Do you actually need special phosphorus fertilizers in the garden?
No, the use of phosphorus fertilizers in home and hobby gardens is - with the exception of a deficiency confirmed by a soil sample - practically unnecessary, especially if the garden is primarily fertilized with manure and compost. Many supposed signs of a phosphorus deficiency in plants can also be traced back to other causes, which is why you should avoid fertilization if possible, simply because of the high proportion of pollutants.
How do I carry out a soil analysis?
Since fertilization should not be carried out if there is a suspected phosphorus deficiency, a soil analysis must be carried out beforehand. Of course, you don't do this yourself. You take soil samples from various places in your garden and send them to a specialized institute for soil analysis. You will then receive an evaluation and fertilizer instructions.
Tip
If algae growth becomes excessive in an aquarium or garden pond, an excessively high phosphorus content could be to blame. You can easily determine this using a commercially available phosphate water test. If there is phosphate contamination, a so-called “PhosphateMinus” product can help.
