This spring has brought significant temperature fluctuations: at the end of March and beginning of April, there were eight warm days, followed by eight cold days, and then a 12-day warm period. Since 25 April, however, the weather has cooled down again. During the warmer days, crops grew vigorously, while cold spells almost brought growth to a halt. These shifting conditions raise a challenging question for farmers: when is fertilisation most effective?
How Does Temperature Affect Fertiliser Performance?
Fertilisers applied to fields are subject to various chemical, biological, and physical processes. For example, nutrients can only move deeper into the soil when mixed with water or slurry. Temperature also plays a crucial role in how effectively plants absorb fertilisers. The cooler the weather, the slower and less efficient the chemical and biological processes in the soil become.
What Do Scientists Say?
As early as 1983, agrochemists E. Raudväli and A. Sirendi emphasised in their article “Current Issues in Nitrogen Nutrition” that applying nitrogen fertilisers in early spring before crops begin to grow is not justified. According to them, nitrogen spread onto frozen soil often disappears without a trace, due to a process called dissimilatory denitrification, which occurs at low temperatures:
2NO₃ → 2NO₂ → 2(HNO) → H₂N₂O₂ → N₂O↑ and N₂↑
Once the soil temperature rises above +7 °C, assimilatory denitrification begins to dominate, during which ammonia (NH₃) is formed. This binds to the soil and becomes available to plants.
How to Apply This Knowledge in Practice?
Based on this understanding, a practical recommendation emerges: for spring-sown crops, nitrogen fertiliser should be applied during pre-sowing tillage. For winter cereals and forage grasses, it should only be applied after vegetation resumes—once the soil is moist enough to allow application without damaging the sward or seedlings. At that point, it is advisable to apply the full nitrogen amount at once for cereals, while for grasses, only the quantity needed for the first cut should be applied.
Conclusion: Don’t Fertilise by the Calendar – Follow the Conditions
Temperature is a key factor in fertiliser performance. Applying fertiliser too early can lead to nutrient losses and reduced yields – even if the fertiliser itself is appropriate. Instead, base your decision on actual field conditions:
- Is the temperature adequate?
- Is there enough moisture in the soil?
- Have the crops entered active growth?
When all these conditions are met, the fertiliser can do its job – supporting crop growth and contributing to yield.