About the calculator

Growing a legume (vetch, forage pea, berseem clover…) together with a cereal (oat, barley, triticale…) is common practice in Tunisia for forage production. The cereal supports the climbing legume, and the legume enriches the forage with protein. But each species still has to be sown at the right rate: too few seeds and the mixture becomes unbalanced, too many and seed is wasted.

This calculator works out the seed quantities of a forage mixture from the share of each species. Starting from the target share of plants per m² for each species in the mixture and its germination rate, it gives the seeding rate of each one needed to reach the overall target density.

You enter:

• the species in your mixture: up to 3 legumes, 3 cereals and, if you wish, one taproot species (rapeseed, forage radish…);

• each species' share of the target plant stand, as a percentage of plants per m² (the total must be 100%);

• the germination rate (GR) of each seed lot;

• the target seeding density, in seeds per m².

The calculator then gives the seeding rate for each species, in seeds per m².

For each species:

seeding rate = target density × species share (%) ÷ (0.8 × GR (%))

The 0.8 coefficient corrects for the fact that only part of the sown seeds emerge.

Example: for a target density of 200 seeds/m², a vetch making up 60% of the stand with a 90% germination rate gives 200 × 60 ÷ (0.8 × 90) ≈ 167 seeds/m².

The calculator suggests three benchmarks, to adapt to your plot:

• 150 seeds/m² in semi-arid zones;

• 200 seeds/m² in sub-humid zones;

• 300 seeds/m² in favourable or irrigated zones.

You can also enter your own value.

It is mainly intended for agricultural technicians and agronomists, to fine-tune advice on forage mixtures. It is also for farmers who simply want to work out their seeding rate, and for agronomy students.