Potassium and phosphorus are the key nutrients to consider in your alfalfa fields fertilisation plan. Fertiliser should be applied as alfalfa starts to regrow.

Management tips for applying the right blend of nutrients to your alfalfa.

With the ability to fix its own nitrogen, Alfalfa doesn’t require the application of nitrogen fertiliser. Because of this, when considering the nutrient plan for your alfalfa fields the key nutrients to consider are potassium and phosphorus rounded out with some targeted micronutrients. It is recommended to time fertiliser application from the end of winter to beginning of spring, when alfalfa starts to regrow.

Potassium (K)

Identify Potasium Deficiency :

  • Potassium is the most important element for growing alfalfa. It improves the productivity and persistence of alfalfa and allows it to better store sugars in the tissues, which strengthens plants’ tolerance to disease, cold and different types of stress. 
  • Potassium deficiency can be identified by yellow dots on both sides of alfalfa leaves. 
  • Alfalfa needs 150 to 250 kg of K/ha, the rate to be varied based on the productivity of the alfalfa, the soil type, and soil testing to understand the K available. 
  • Application of K is recommended in sulphur-potassium form split into two applications in excess of 200 kg/ha. 

Recommended Potassium (K) intakes*

Results of Soil Analysis

Phosphorus (P) :

  • Alfalfa needs highly bio-available forms of phosphorus to reach its yield potential.
  • Phosphorus is very important for the development of roots and the longevity of the crop.  
  • Phosphorus-deficient alfalfa can be spotted by its purplish-blue colour on the leaves and purplish-red colour on the stem and under the leaves. 
  • Alfalfa needs 60 to 70 kg of P/ha at seeding and then every year at the end of winter. This volume needs to be customized based on the type of soil, the available phosphorus in the soil and what has been left in the soil from previous crops.

Recommended Phosphorus (P) intakes*

Results of Soil Analysis

More about alfalfa

Check Your Soil’s pH

  • Although alfalfa can germinate with a very low pH, the growth of seedlings is very limited in soil with a pH of less than 5.5,
  • In soils with a low pH the development of rhizobium bacteria will be very difficult, limiting the development of nodules. 
  • On acidic soils it is important to add lime to target an optimal pH of 6.5. 
  • When the soil pH is higher than 6.5, alfalfa can develop a boron deficiency. 


Identify Sulphur (S) deficiency :

  • Alfalfa becomes pale green to yellow and its protein content can fall by up to 3 points in the case of sulphur-deficiency.
  • It is recommended to add 50 to 100 kg/ha in risk situations (soil that is filtering, superficial, low in organic matter, hydromorphic, etc.)  


  • Alfalfa is particularly sensitive to magnesium, boron, copper and molybdenum deficiencies.
  • Fertilisation should be customised to soil analysis results on a case-by-case basis. 
  • Alfalfa generally needs 50 kg/ha of magnesium, 500 g/ha of boron, 500 g/ha of copper and 100-300 g/ha of molybdenum. 

* Source: Arvalis 

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