Yellow trefoil (medicago lupulina) also known as black medick is a short lived annual/biennial legume. A low growth habit makes it a common choice for undersowing as well its use for soil improvement.
Frequently used with white clover in an undersowing mixture, this mixture will fill the base of a main crop brassica or cereal without affecting its yield. It reduces weed competition, adds organic matter and fixes nitrogen. It can also be used with annual species like persian clover, crimson clover, mustard and phacelia as a short term soil improving green manure.
When to Sow: April - May is the ideal time for sowing in the spring. If it is to be under sown in spring cereal, it should be sown in May, after the cereal is established. Mid - late August is the best time for autumn sowings. Establishment is less likely to be reliable if sowing extends too far into September.
Sowing Rate: 1 g/m2 - 4kg per acre - 10kg per ha.
Preparation: For a direct sowing the most successful results come from sowing into a newly prepared seedbed. Aim to cultivate the top soil to about 5cm, with a light cultivator or discs. The finished seedbed should be fine but firm, with no clods. Several passes with a cultivator may be needed to achieve this.
If used as an undersown mix to a cash crop, the seed is either broadcast or shallow drilled as soon as the cash crop has been sown. In the case of cereal cash crops, the cereal seedlings may be given several weeks to emerge before broadcasting the undersown seed.
Sowing: Seed of yellow trefoil is very small and should be broadcast or drilled at a shallow depth (not more than a few mm). Sowing too deep will reduce the germination dramatically. The soil should be rolled after sowing to increase seed to soil contact.
Management: Yellow trefoil can be cut if there is a severe annual weed problem. Although it is an annual plant, it can successfully regenerate itself through seeding.
It will survive over the winter and flower the following year. To terminate reliably it will need to be ploughed or incorporated.
Date Posted: 13th January 2023