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How to quantify the impact of a cover crop on the fertility of soils

Sowing a green cover crop may seem like an extra cost for your fields. However, it will help restructure the soil, nourish microbiota, and improve biodiversity. Moreover, cover crops also play a key role in improving soil fertility.
One clever method has been created in France to estimate the impact of a cover crop on soil fertility. It is called the MERCI method, and it is easy to use in your fields.

We will present you with the method in detail and why it is of interesting use for your parcels.

What is the MERCI method:

This method has been developed in France in 2010. Scientists analyzed various species comprised in a cover crop to determine their nutrient content.
While they grow, plants will mobilize nutrients from the ground to develop their stems, leaves, or roots.
Once the plant is terminated, those elements will again be made available for the next cash crop all the while improving soil biology and in consequence, soil fertility.
Nitrogen is the most important nutrient for all crops. As it is leachable, cover crops will help in reducing leaching it in the belowground and raise its availability for the next cash crop.

Additionally, legume species present in the premium cover crops of the Cargill RegenConnect® program, will fix this valuable nitrogen from the atmosphere. The use of legumes is an economical strategy to reduce the need for synthetic nitrogen. If the farmer can calculate the amount of nitrogen fixed in the soil and that will be available to the following crop, the calculations will also be accurate.
Sulphur is also a nutrient that can be leachable. The quantities are lower in a cover crop compared to nitrogen, but it is still an essential element that will remain in the field.
Other elements are also brought back in the topsoil by cover crops, but the impact is less significant, as there is less economy to be made: those elements are already available in the soil solution (except for phosphorus that can be released by some crops such as mustard or fava bean.

How to do the MERCI method:

It is simple and not too time consuming:

You will have to go to your field and collect samples from 1 square meter. We recommend you take at least 3 samples from each field.
Then proceed to dry the plants or take away as much water as you can (1 mm (about 0.04 in) of water remaining = 1 T).
Separate the distinct species in the cover crop and weigh them one by one to obtain a more reliable value.
You can then directly use the French web site or send us your weighing data at ADD ADRESS.
Value datasets have been calculated in France. It may not be as precise for your country but that will give you a general overview of what you can expect as a return on investment from your cover crop in terms of fertility.

105 units of nitrogen were mobilized in those 4 T of dry matter cover crop composed of Brassicaceae, sunflower and legumes. 48 will be released in the spring with an economy of potentially 72€/ha (1,5€ / kg of nitrogen). Most of the cover crops with a satisfactory biomass (above 2 T Dry mater) will release at least 30 units of nitrogen for the next cash crop.

20 units of phosphorus, 150 of potash and 25 of Sulphur (12,5€/ha) are also in it. That cover crop will make disponible 90€ / ha that would have been leachable.
To conclude, cover crops represent a crucial tool in your transition to regenerative agriculture. Using the Mercy method will help you quantify their benefits in fertility and further convince you they are worth the Investment you make when you purchase and sow them.
If you need more information do not hesitate to contact us!

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