Photo Olivier Cor

by Olivier Cor

Directeur agronomie


Organic matter provision, even though essential, often poses a conundrum for farmers. Here are four tips for assessing your soil’s organic matter needs.

“The notion of humus which is the soil resulting from the decomposition of plants, is still relatively unknown to farmers, notes Olivier Cor, engineer and agronomist for Lallemand Plant Care. Some people think there is a right or wrong level of humus, but the issue is much more complex than that.”

The key is to regularly feed the soil with the right amount of plant and animal organic matter. And for that, there is an art to it.

According to the expert, to properly feed your soil, you should not rely on your instincts. You need a good strategy.

1 - Avoid these two mistakes

Many farmers make massive provision of organic matter but only once every three or four years. However, the best thing to do is to regularly feed your soil.

“We must not leave the soil exposed and we must ensure that the cultivated plots have enough to feed on every year. Annual or biennial provisions are therefore preferred, combined with cover crops in winter,” says Olivier Cor.

Another common practice – but one that needs to be avoided – is to calculate the storage size based on the amount of manure produced.

This way, the pit is full in the winter, when the soil has little need. “With this reasoning, provisions are made at a time when the soil has difficulty digesting manure,” says the agronomist.

2 - Respect the three golden standards

To ensure that you have an optimal provision of organic matter, you should:

  1. Fertilize regularly: this will allow the soil to restructure itself more easily, especially in case of compaction.
  2. Diversify the nature of the organic matter: the soil’s diet (like ours!) must be balanced, in order to avoid deficiencies and excesses. In other words, don’t always add the same matter on the same plots.
  3. Adapt the provision of organic matter to the soil’s functioning speed: on a waterlogged soil, for example, you should bring in organic matter that has already been composted.

3 - Check if your soil is decomposing the plants well

To find out if your soil has good humification dynamics, you can:

  • Smell the earth: it is a good sign if it smells of fresh earth. On the contrary, if it smells like rotten eggs or sulfur, that means that there is a problem.
  • Check the soil structure: if there is a crust on the surface or some compaction, it means that the quality of the humus needs to be improved.
  • Walk your field regularly: check the degradation rate regarding crop residue. You should be able to see a change after three or four months. Here’s a tip: take a before and after picture and compare them.

4 - Interpret your soil analysis

Carrying out a soil analysis every four or five years can be useful to complete the annual diagnosis, but you still need to know how to interpret it.

Olivier Cor recommends that more importance be given to the evolution of the C/N ratio than to its value. “For example, if it is increasing, it is because carbon degradation is not occurring properly. It’s a sign of organic feedstock problems” he argues.

The pH has an influence on the transformation rate of the organic matter. “You have to make sure that the pH does not fall below 5.8” advises the specialist.

This is because a soil that is too acidic leads to a slower and incomplete transformation of fresh organic matter.

The result? The carbon cycle slows down and the soil’s nutrients decrease.

The agronomist also advises that soil analysis should only be done on worthwhile plots. “It is best to keep a close eye on the better performing fields than to waste time and money trying to improve the few plots that have problems! “

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