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Soil & Soil life


Microorganisms have accompanied plants since their appearance on land. The very appearance of the first plants is a history of plant-microorganism symbiosis. We now know that the first plants which lived exclusively in the oceans were able to colonize the terrestrial environment thanks to their symbiotic association with fungi. These associations gave the first symbiosis which we call mycorrhizae (plant-fungi association).



Bacteria, yeasts and fungi were already present on dry land when plants began to grow there and their history has been intimately linked ever since. This microbial colonisation is so old and widespread that many mechanisms incorporate microorganisms into their daily routines – such as nutrition, development or immunity…












A good ploughing airs the soil…











Yes and no. Ploughing is primarily a method of weeding in agriculture. The soil is an organised and structured living environment. A ploughing disrupts and destroys thousands of microscopic lives or not. These are very useful for the farmer and allow plants to find everything they need to grow:

  • mycorrhizal fungi (a microscopic fungus) that make nutrients available directly to the roots,
  • earthworms that aerate the soil,
  • micro-fauna including bacteria, algae, fungi.


Frédéric Thomas, farmer and editor-in-chief of TCS magazine, explains




  • how the soil is organized from the surface,
  • the difference between an amendment and a fertilizer,
  • how the biological activity of the soil is going to be revived by plant covers that bring organic matter. The plants must be allowed to degrade with the help of microorganisms and earthworms,




It is the vital basis for the correct functioning of the soil and is found in different forms in the soil. This will depend on the state of decomposition of the organic matter that has been or is occurring. ” The soil can contain very recent organic matter derived from animal or vegetable matter just as it can contain organic matter going back 7,000 years! ” says Olivier Cor head agronomist and head of R&D at Lallemand Plant Care France.

This transformation (or mineralisation) of “fresh” organic matter into humus, which is typically black in colour, is called the “humification process”.


“The dynamics of this greatly depends on the way soils are worked, their composition, the weather, the environment, the plant cover present (flora) including trees and all of these can condition, through to a major extent, the nature of the organic matter present in the soil”, continues Olivier Cor. For example, depending on the initial composition of the plants in the organic matter – “improving” (rich in nitrogen) or difficult decomposition (acidifying) – the speed of humification will be more or less rapid.

From a biochemical point of view, “everything revolves around the carbon cycle”…

… mobilised by the plant, degraded and then reintegrated, says Olivier Cor. “In a soil, the centre of life is carbon … Like an engine, which will run well or not depending on the circumstances, humification corresponds to mineralisation (see above on this page) and by the reorganisation of the organic debris by the action of microorganisms. The fungi are the first to work to break the solid carbon chains, and then the bacteria intervene to finish the process. Obtaining “in the end” humus, totally degraded organic matter which is mainly composed of black or grey humic acids, fulvic acids and carbon rich molecules

These numerous living microorganisms, involved in this process, are therefore of major importance, impacting the dynamics and rate of degradation of carbon in the soil. “All these living things are the life of the soil!” concludes the agronomist. They will turn this ‘carbon engine’ more or less quickly; organic matter being the reservoir… “Managing organic matter means managing the wealth and life of your soil. If you do not give them enough food and when they need it, the engine will stall!

But, coming back to humus… What is it used for?

Humus first serves as a “pantry” for plants

When fertilisers are applied to the soil, the plants are fed directly, but used alone; these fertilizers are far from sufficient:

Organic matter, reorganized during the humification process, is also an important source of nitrogen for plants, which allows it to draw when the plants need it and not only when fertiliser is added.

For Olivier Cor, this concept is essential in agriculture, and even more important than fertilisation itself, because it is this that will allow (or not!) the achievement of a good return from crops. “If one took the time to compare the quantities of nitrogen contributed by humus and by fertilizers, one would have to transport the equivalent of several semi-trailers loaded with ammonium nitrate!”

If one looks more closely, during the mineralisation of organic matter, microorganisms mobilise a large amount of the nitrogen provided by fertilisers as well … which will then return to the plant.

Indirectly, organic matter therefore gives efficiency to mineral fertilizers.

Humus also plays a vital role in structuring the soil.

The stable part of humus, formed of humic compounds, attaches to clay particles, forming the clay-humic complex (CAH). This guarantees the structural sustainability of the soil thanks to micro-porosities and ensures stability against external aggressions: rain, compaction caused by the passage of agricultural machinery etc. Basically a well-balanced soil, with respect to organic matter from regular contributions, will therefore restructure itself and more rapidly, especially for example where agricultural equipment has operated, says Olivier Cor.

It also provides it more natural resistance to compaction. In addition, the clay-humic complexes allow the storage of water and its release to plants, when they need it, or the good penetration of the soil by air, roots and the supply of water and minerals. It is wrong to say that organic matter is a water pump, Olivier wants to clarify. On the contrary, it allows storage!

The clay-humic complexes, which retain exchangeable cations (Ca2 +, Mg2 +, K +, Na +, etc.) on their surfaces can be made available to plants and also protect soils from the risk of losses by leaching. In this situation humus participates as a reservoir of chemical fertility for the soil.

Finally, organic matter is used to feed soil microorganisms: with no organic matter there are no living beings to degrade it, so there is no functional carbon cycle! Earthworms, which play a fundamental role in the production, structuring, maintenance and productivity of agricultural soils, also need fresh organic matter to feed themselves; this is also the place that they live.


Humus is an unknown concept to farmers (even today)…

This fact gives rise to misinterpretation and bad technical decisions, “says Olivier Cor. The interpretation of the humus rate – and the C / N ratio – by a simple soil analysis every 3-4 years, at a “T” instant, is an example: “There is neither a good nor a bad rate of humus, justifies the agronomist. The question is much more comprehensive than that! If you concentrate on this criterion alone you will forget other vital actions!”


Important questions to consider include whether microorganisms in the soil have enough to eat, in other words, if they are provided with adequate and regular quantities of animal and plant derived organic matter that they can decompose and feed on. “If this is not the case, then the engine that needs to be running smoothly will stall!“ Too many farmers, for example, use massive, single-time supplies of organic matter only every 3-4 years. Another harmful practice that needs changing is that: when establishing a manure plan, the storage size is calculated based on the amount of manure produced, but the pit is full in the winter, at a time when the soil has few needs. “With this reasoning, inputs will begin to take place out of necessity at a time when the soil will have difficulty assimilating the manure,” laments the agronomist.


Annual or bi-annual spreading is fine but it must be associated with plant cover in the winter is therefore preferred to avoid bare soil and ensure that the plots have enough to ‘consume’ year by year. A regular supply of organic matter will also enable the soil to restructure itself more easily and on  its own, in case, for example, of compaction. Likewise, one should also take care to diversify the nature of the organic matter brought: “Never always put the same on the same plots, advises Olivier Cor. The diet must be balanced so as to avoid deficiencies and excesses, just as is necessary for us!” The inputs must also be adapted to the operating speed of the soil. On a hydromorphic soil, for example, it is better to add organic matter that has already been composted. From this naturally follows the second question

Does my soil possess good humification dynamics?…

Without just restricting ourselves to a simple soil analysis the answer to that question can be provided by smelling the earth: “The smell of fresh earth is a good sign, but the smell of rotten egg, of sulphur, is a much less encouraging sign!” It is also necessary to check the soil structure, to see if there is a problem with sealing or compaction. “If that is the case it should ring an alarm bell on the quality of the humus” he continues. Finally a last point: perform a regular ‘land inspection’ to check the rate of degradation of crop residues. After 3 or 4 months, change should be visible revealing degraded residues. “If that is not the case then there is a problem, adds Olivier Cor. “To help you, you can take a simple photo with your mobile phone, before and after, and compare.”

Putting these simple tips into practice every year, can help. Only then, the additional use of soil analysis, every 4 or 5 years, will complete the diagnosis. “Only carry out analysis on the plots that are worth it,” concludes the agronomist. “It is much better to take the time to closely inspect those that are high yielding than to waste time and money trying to improve the yields of plots that have problems! “

Finally, regarding analysis and the C/N ratio, Olivier Cor recommends attaching more importance to its evolution than its value: “If it moves (increasing for example that means that the carbon degradation is not functioning correctly. This could be a sign of possible problems with compaction, or to do with supplies of organic matter”. The same advice applies to pH: this influences the rate of transformation of organic matter. “It must be watched that the level does not descend too much, not below 5.8, in order to guide carbon degradation towards a more rapid cycle.”

An acid pH leads to a slower and more incomplete transformation of fresh organic matter (the C/N increases and can reach values of 11 to 12) as the carbon cycle slows down, the availability of nutrients from the soil decreases.


General principles

Prebiotics are molecules that constitute a nutritive support that can be used and assimilated by populations of microorganisms. These substances are then metabolized by microorganisms via different physicochemical processes, including hydrolysis and fermentation.

Prebiotics have recently been used in human and animal nutrition to allow the stimulation and the good development of certain intestinal bacteria (bifidobacteria), allowing in particular the digestion of fibres and other compounds not utilisable by humans and/or animals. By increasing the beneficial microbial populations, these prebiotics act indirectly on the phenomena of chelation and assimilation of minerals, and also participate in making the immune system function properly.


Their application in crop production

Prebiotics allow the stimulation of beneficial bacteria that are naturally present in the environment. These molecules are all capable of stimulating the intestinal microflora as well as stimulating other bacterial populations, especially those developing in agricultural soils.

The phytostimulanting rhizospheric bacteria, intimately linked to the rhizogenesis in sown crops, can therefore be activated by the use of prebiotics applied to the soil.

LALLEMAND PLANT CARE is a pioneer company in the development of prebiotics used in crop production. In particular, it markets various yeast derivatives designed to carry out this role in soils and other substrates.