Introduction
Alfalfa, as a perennial legume crop of high nutritional value for fodder, has the capacity for biological nitrogen fixation through symbiosis with root bacteria. However, its nutritional adequacy largely depends on the rational supply of macronutrients, mainly phosphorus (P), potassium (K) and sulphur (S), which determine the yield and longevity of the plantation.
Nitrogen: necessary only under certain conditions
In fields with good microbial activity and a history of legume cultivation, nitrogen addition is not necessary. On the contrary, in soils where alfalfa is established for the first time or in low temperature/arid field conditions, a limited addition (4-5 N units/ha) during establishment is recommended until nitrogen fixation is fully activated.
Phosphorus: critical for the root system and longevity of the plantation
Phosphorus enhances the establishment and function of the root system. The annual requirement is 4-6 units of P₂O₅/ha, while during establishment, especially in poor soils, a dose of up to 8-10 units is recommended.
Potassium: a key regulator of physiological functions and resilience
Alfalfa has a high need for potassium, especially due to repeated cutting. Each tonne of dry matter removes about 15-18 units of K₂O, so the annual requirement for yields of 2-3 tonnes/ha. is 30-50 units. Potassium contributes to water stress tolerance, photosynthesis and overall feed quality.
Sulphur and minerals
Sulphur (S) is involved in protein synthesis and in soils with low organic matter or light texture, it can be a limiting factor. 2-4 units of S/ha/year are recommended. As regards trace elements, boron (B) is essential, especially in alkaline soils where its availability is reduced. Monitoring the concentration by foliar diagnostics is particularly useful in intensive crops with very high requirements.
Time of application and forms
Basic fertilisation: carried out before sowing or at the beginning of spring, before germination.
Surface fertilization: repeated every year, preferably after each cut, to replenish the removed elements.
Maintaining adequate levels of P and K is crucial for efficient plantation management for 3-5 years.
Conclusion
Alfalfa, despite its natural ability to fix nitrogen, has increased requirements for phosphorus, potassium and sulphur. Their lack leads to a decrease in productivity and premature exhaustion of the plantation. The fertilisation strategy should be based on soil analysis, be targeted and repeated, and supported by geotechnical guidance. Sufficiency of macronutrients enhances the stability, protein content and overall quality of the feed produced.
