Nitrogen fertilisers for different crops
· Valerii Korolko · 7 min read
When nitrogen fertilisers are needed
Without it, normal shoot growth, leaf formation and yield accumulation are impossible. Potassium is its excellent helper: working in tandem, it regulates the water balance of cells, strengthens plant immunity and improves fruit quality. Let us look at the use of nitrogen-phosphorus-potassium fertiliser.
The role of nitrogen and potassium
Nitrogen is responsible for vegetative growth – that is, for green mass, stems and leaves. If leaves turn pale from the bottom up, growth slows down and new shoots are weak, this is a signal of nitrogen deficiency.
Potassium increases resistance to drought, disease and temperature fluctuations. It is especially needed when the plant moves from growth to fruiting. Nitrogen-phosphorus-potassium fertiliser is the most balanced solution for most crops: it covers the need for three key elements at once and simplifies the care of plantings.
What nitrogen-potassium fertilisers are used for
- A spring start after winter – to wake the plant up and give growth a push.
- The period of active vegetation – to support the build-up of greenery.
- Preparation for fruiting – to balance nutrition before flowering.
- Recovery after stress – disease, transplanting, drought.
Pure nitrogen fertilisers for the vegetable garden are used mainly in spring and in the first half of summer. In the second half of the season, formulas with a higher potassium content work better.
It is important to remember: an excess of nitrogen is also harmful. If a plant is overfed, it starts to "run to leaf" – it produces a lot of leaves and shoots, but flowering and fruiting may worsen. Therefore, feeding plants with nitrogen and its application rates must always be selected taking into account the crop, the stage of development and the growing conditions.
Nitrogen fertilisers for vegetables
Vegetable crops actively consume nitrogen during the build-up of green mass and especially at the start of fruiting. As flowering and fruiting approach, it is important not to overload the plantings. That is why a nitrogen-potassium fertiliser for vegetables often turns out to be a better solution than purely nitrogen feeding.
For cucumbers
Nitrogen fertilisers for cucumbers are applied in several stages:
- When planting seedlings – a small dose of nitrogen to help them establish.
- During active growth of the vine – increased nitrogen nutrition.
- At the start of flowering – nitrogen is reduced and the share of potassium is increased.
How to apply nitrogen fertilisers for cucumbers in a greenhouse and in open ground is an important question. In a greenhouse, because of the limited volume of soil and higher temperatures, the fertiliser is absorbed faster, so doses are reduced by 20–30%, but applied more often – once every 10–12 days. In open ground, feeding is applied taking into account the weather and the condition of the soil.
A good option for cucumbers is potassium nitrate (saltpetre): it contains both nitrogen and potassium without excess chlorine, which cucumbers do not tolerate.
For potatoes
Potatoes consume nitrogen mainly in the first half of the growing season – until the haulm closes over. After that, an excess of nitrogen is harmful: tubers accumulate nitrates, while the haulm continues to grow at the expense of the yield.
Fertilisers for potatoes with nitrogen, application rates: they are applied at planting in the form of ammonium nitrate (15–20 g per sq. m) or urea (10–15 g per sq. m), and at the budding stage growers switch to potassium-phosphorus feeding. Exceeding the stated rates is not recommended.
Nitrogen fertilisers for berries
Berry crops are sensitive to nutrient balance: an excess of nitrogen gives lush greenery, but reduces the sugar content of the berries and makes plants vulnerable to disease.
For strawberries
Nitrogen fertilisers for strawberries are applied twice, and observing the timing is critical here:
- In early spring, as soon as the snow melts – for recovery after winter.
- Immediately after fruiting – for the formation of new fruit buds.
Nitrogen fertilisers for strawberries, when to apply: nitrogen is not applied during flowering and fruiting – it reduces berry quality. The best option is the ammonium form of nitrogen (ammonium sulphate), which acidifies the soil, something strawberries like.
For raspberries
Which nitrogen fertilisers suit raspberries is a question that gardeners often ask. Raspberries are active consumers of nitrogen, especially at the start of the season. Their root system is shallow, so the fertiliser is applied to the surface with obligatory watering.
If the bushes grow on poor soil, nutrition will be needed more regularly. If the plot is fertile, feeding should be more cautious. Feeding scheme:
- Early spring – nitrogen fertiliser at the root (ammonium nitrate or urea).
- After 3–4 weeks – repeat feeding during active shoot growth.
- End of July – August: nitrogen is excluded, only potassium and phosphorus are applied.
Nitrogen fertilisers for ornamental crops
For roses
Nitrogen fertilisers for roses are a topic where it is easy to make a mistake. Roses need nitrogen, but strictly by phase:
- After winter pruning – moderate nitrogen feeding to wake the plants up.
- Before the first flowering – another feeding with a predominance of nitrogen.
- After each wave of flowering – a switch to potassium-phosphorus formulations.
From August, nitrogen fertilisers for roses are excluded completely: young shoots that grow in autumn do not have time to lignify and freeze in winter.
Chlorine-containing forms (potassium chloride) are not suitable for roses. The best choice is potassium nitrate or special complex fertilisers for roses.
For flowers in open ground
Nitrogen fertilisers for flowers in open ground are used exclusively during the growth of green mass. Annual and perennial flowers (petunias, marigolds, dahlias, phloxes) are fed with nitrogen from planting until buds appear. As soon as flowering begins, nitrogen is reduced, otherwise the plant "runs to leaf": the leaves are large, but there are few flowers.
For houseplants
Nitrogen fertiliser for houseplants should be liquid or water-soluble – it is easier to dose and safer for the roots in the limited volume of a pot.
Houseplants are fed with nitrogen only during the period of active growth – from March to August. In autumn and winter most of them are dormant and do not need fertilisers.
Signs of nitrogen deficiency in houseplants: yellowing of the lower leaves, slowed growth, small new leaves.
For orchids
Orchids are a special case. They need very small doses: the standard dose for houseplants is divided by 4. Fertiliser for orchids should contain nitrogen in a minimal amount and no urea – pure urea is poorly absorbed through orchid roots. During dormancy and when there is no growth, orchids are not fed at all.
How to choose nitrogen fertilisers for different crops
Open ground / greenhouse
Nitrogen fertilisers for greenhouses, how to choose? The fertiliser should be easily soluble and free of ballast components (chlorine, sodium). In protected ground the soil is not washed by rain, so salts accumulate faster. Nitrate forms of nitrogen and potassium nitrate work better here.
In open ground, ammonium forms (ammonium nitrate, urea) are acceptable – they are cheaper and are well absorbed when moisture is present.
Nitrogen-potassium fertiliser for soil with a high clay content is applied in spring and worked in to a depth of 10–15 cm. In light sandy soils, the fertiliser is applied in small doses but more often, as it is quickly washed out.
Intensity of cultivation
With intensive cultivation (greenhouse, frequent watering, dense planting), the need for nutrition is higher, but the risk of overdosing is also higher. Split application is used – in small doses once every 1–2 weeks.
With extensive cultivation (a dacha, infrequent visits), slow-release forms or fertilisers with a prolonged effect are chosen.
Which nitrogen fertilisers suit trees: fruit trees are fed with nitrogen only in spring – before flowering and immediately after it. The application rate of urea for an adult tree is 150–200 g per plant. Summer and autumn application of nitrogen to trees is contraindicated – it weakens the wood before winter.
Soil type
| Soil type | Recommendations |
| Acidic (pH below 6) | Nitrate forms of nitrogen, not ammonium ones |
| Neutral (pH 6–7) | Any forms |
| Alkaline (pH above 7) | Ammonium forms (they acidify the soil) |
| Light (sand) | Frequent small doses |
| Heavy (clay) | A single spring application, worked into the soil |
Common mistakes in use
- Applying nitrogen in autumn. This stimulates the growth of new shoots that do not have time to ripen before the frosts. Nitrogen is for spring and the first half of summer only.
- Exceeding the dosage "to be safe". An excess of nitrogen leads to root burn, the accumulation of nitrates in fruit and weakened plant immunity.
- Applying fertiliser to dry soil. A concentrated solution burns the roots. Always water before feeding, and after it too.
- Using one fertiliser all season. A plant's needs change: in spring it needs nitrogen, before fruiting – potassium and phosphorus. The feeding scheme must change along with the growth phase.
- Ignoring the form of nitrogen. Urea, ammonium nitrate and potassium nitrate are different substances with different rates of absorption and different effects on soil pH. The choice depends on the crop, the soil and the season.
- Not taking the composition of irrigation water into account. Hard water with a high pH reduces the availability of fertilisers. In greenhouses this is especially relevant.
How do you choose a nitrogen-potassium fertiliser correctly? It is not a one-off feeding but a system. Start by analysing the condition of the plants and the soil, choose the appropriate form and follow the application scheme throughout the season.
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