Maximising the Potential of Your Lucerne

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

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

Thanks to its ability to fix its own nitrogen, lucerne doesn’t require the application of nitrogen fertiliser. As a result, when considering the nutrient plan for your lucerne fields, the key nutrients to consider are potassium and phosphorus, rounded out with some targeted micronutrients. It is recommended to apply fertiliser between the end of winter and the beginning of spring, when lucerne starts to regrow.

Potassium (K)

Identifying a potassium deficiency:

• Potassium is the most important element for growing lucerne. It improves the productivity and persistence of lucerne and improves its ability to store sugars in the tissues, which strengthens its tolerance to disease, cold and different types of stress. 
• Potassium deficiency can be identified by yellow dots on both sides of lucerne leaves. 
• Lucerne needs 150 to 250 kg of K/ha; the rate varies depending on the productivity of the lucerne, the soil type and soil testing to ascertain how much potassium is available. 
• It is recommended that you apply potassium in sulphur-potassium form, split into two applications in excess of 200 kg/ha. 

Recommended potassium (K) intakes*

Phosphorus (P)

• Lucerne needs forms of phosphorus with a high degree of bioavailability to reach its yield potential.
• Phosphorus is very important for the development of roots and the longevity of the crop.  
• Phosphorus-deficient lucerne can be spotted by the purplish-blue colour of its leaves and the purplish-red colour of the stem and under the leaves. 
• Lucerne needs 60 to 70 kg of P/ha at seeding and then every year at the end of winter. This volume needs to be adapted 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*

More about lucerne

Read Lucerne Crop Essential

Check the pH of your soil

• Although lucerne can germinate in soils 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. 
• It is important to add lime to acidic soils to target an optimal pH of 6.5. 
• When the soil pH is higher than 6.5, lucerne can develop a boron deficiency. 

Micronutrients

Identifying a sulphur (S) deficiency:

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

Trace elements

• Lucerne is particularly sensitive to magnesium, boron, copper and molybdenum deficiencies.
• Fertilisation should be customised based on the results of a soil analysis on a case-by-case basis. 
• Lucerne 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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