SOIL / SOIL LIFE
What if the soil functioned like a car engine?
The vital basis for the functioning of the soil, humus,is found in different forms in the soil depending on the state of decomposition of the organic matter:
“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!” declares Olivier Cor (agronomist, head of R&D at Lallemand Plant Care France). This transformation (or mineralization) of “fresh” organic matter into humus, decidedly black in colour, is called the “humidification process”.
“Its dynamics greatly depends on the way soils are worked, on their composition, on weather, the environment – flora including trees – or even on the plant cover, and all these condition to a major extent the characteristics of the organic matter present in the soil”, continues Olivier Cor. So, for instance, depending on the initial “enhancing” composition of organic matter of plants (rich in nitrogen) or difficult to decompose (acidifying) the speed of humidification will be more or less fast.
From the biochemical point of view, “everything is based on the carbon cycle”
Carbon, organized by the plant, degraded then reintegrated in the soil, is the core of life, says Olivier Cor.…just like an engine, that runs well or not according to circumstances!. Humidification indeed depends on the reorganization of the organic debris by the action of microorganisms:
- firstly, the fungi that break the solid carbonaceous chains
- then by the action of bacteria.
The obtainment ultimately of humus, a totally degraded organic matter, is mainly composed of black or grey humic acids, fulvic acids and carbon rich molecules.
These numerous live microorganisms involved in the process have therefore a major role to play impacting on the dynamics and rate of degradation of carbon in the soil. “All these live beings are the very life of the soil!”, concludes the agronomist. They cause this carbon engine to run faster or slower, the organic matter being represented by the tank.” Organic matter management is therefore a matter of managing the richness and the life of your soil. If you do not give it enough to consume when it needs it, the engine will stall!
But, coming back to humus… What is it used for?
Humus is first of all the plants’ larder’
When fertilizers are spread, the plant is directly fed, but alone, fertilizers are far from being sufficient: “The organic matter, reorganized during the humidification process is also a significant source of nitrogen for the plant enabling it to be drawn on when it needs it and not only when fertilizers are spread”, the agronomist continues.
According to Olivier Cor, this concept is “vital” in agriculture, even more important than fertilization itself, because it is this that will allow it (or not!) to obtain a satisfactory crop yield. “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 nitrates!” , he chuckles. If one looks more closely, during the mineralization of the organic matter, the microorganisms organize a large percentage of the nitrogen contributed by fertilizers… that they will later give back to the plant. “Indirectly, the organic matter provides efficacy to the mineral fertilizers”, rounds off the agronomist.
Humus also plays a structuring role for the soil!
The stable part of humus, formed by humic substances, are bound to clay particles forming “clay-humic complexes”. This ensures the structural sustainability of the soil by means of micro-porosities and provides stability in respect of attacks from the exterior: Rain and soil compaction due to the movement and working of agricultural machinery, etc. “A basically well balanced soil in respect of organic matter by regular contributions will therefore be restructured of itself and more rapidly, in cases, for instance, where agricultural equipment operates”, explains Olivier Cor.
“It also provides more natural resistance to compaction”. Furthermore, clay-humic complexes enable the storage of water and its restitution to the plant when it needs it, or even good penetration of the soil by air, by roots and their supply of water and minerals. “It is untrue to say that organic matter is a water pump, he feels bound to point out. On the contrary, it enables its storage!”
Clay-humic complexes that keep on their surfaces exchangeable cations (Ca2+, Mg2+, K+, Na+…) will be made available to plants and also protect soils from the risk of loss by leaching. In that sense, humus participates in the reservoir of chemical fertility of the soil. Lastly, organic matter is used to feed the microorganisms in the soil: Without organic matter, there are no live beings to degrade it, therefore no functional carbon cycle! Earth worms that play a basic role in the production, structuring, maintenance and productivity of agricultural soils also need fresh organic matter to be nourished and to live there.
Organic matter: the right questions relating to contributions
Humus is an unknown concept to farmers (even today)…
“That gives rise to false interpretations and bad technical decisions” affirms Olivier Cor. The interpretation of the percentage of humus – and of the C/N ratio – by a simple analysis of the soil every 3 to 4 years, at a moment “T” is one example: “There is neither a good nor a bad humus percentage, underscores our agronomist. The question is much more global than that! If you concentrate on this criterion alone you will forget vital actions!”
Among the important questions to be asked, for instance, the question of knowing whether the microorganisms present in the soil have the wherewithal to feed themselves, or in other words, are they provided regular and sufficient quantities of animal and plant organic matter that they can decompose? If that is not the case the engine will stall!” Too many farmers, for instance, add massive amounts of organic matter, once only, every 3 or 4 years. Another bad habit to change: when a manuring programme is drawn up, the storage space is calculated according to the amount of manure produced, but the pit is full in the Winter, at a time when the soil’s needs are few. “Following this reasoning, spreading takes place at a time when the soil will assimilate the manure with difficulty,” deplores the agronomist.
Annual or bi-annual spreading, YES, but associated with plant cover in the Winter!
Annual or bi-annual spreading associated with plant cover in Winter must be opted for in such a way as to avoid bare soils and to make sure that plots of land have enough to ”consume” year by year. Regular additions of organic matter will also enable the soil to restructure itself more easily and of itself in the event, for instance, of compaction. Likewise, one should also make sure that the characteristics of the added organic matter are diversified: “Never put the same additions on the same plots” advises Olivier Cor. “The alimentary regime must be balanced in order to avoid deficiencies and excesses, just like for us!” Additions must also be appropriate to the functioning rate of the soil. For instance, on hydromorphic soils it would be best to spread organic matter that is already composted. This leads, naturally enough, to the second question:
Does my soil possess good humification dynamics? …
Without, for all that, restricting ourselves to a simple soil analysis. The answer can be provided by smelling the earth: “A smell of fresh earth is a good sign, but the smell of broken eggs or sulphur is a much less encouraging sign!”. You must also check the structure of the soil, to see if there is no problem of sealing or compaction. “If that is the case that should ring an alarm bell on the quality of the humus” he continues. A last point: Carry out 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, there is a problem” adds Olivier Cor. “You can easily find out for yourself by taking a photo with your telephone, one before, one after, and comparing them.”
Put this basic advice into practice every year; it could be helpful. Only then, as a backup, should you resort to soil analyses, every 4 or 5 years, to complete diagnoses. Only carry out analyses on plots of land 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 yours time and money in trying to enhance the yields of plots that are problematic!”
Finally, relative to the C/N ratio, Olivier Cor recommends that you place greater importance on its evolution than onits value: “If it changes (for instance, by increasing) that means that the carbon degradation is not functioning correctly. Sign of possible problems of compaction, or of supplies of organic matter”. Same advice for pH: this affects the rate of transformation of the organic matter. “You must watch out that it’s level does not descend too much – not below 5.8 – in order to guide carbon degradation towards a more rapid cycle.”
An acid pH brings about a longer and more incomplete transformation of fresh organic matter (the C/N increases and can reach readings of from 11 to 12), the carbon cycle slows down, the availability of nutrients by the soil diminishes.
Prebiotics are molecules that make up nutritive supports that are usable and assimilable by microorganism populations. These substances are then metabolized by microorganisms via various physico-chemical processes, especially hydrolysis and fermentation.
Prebiotics have recently started to be used in human and animal alimentary products the aim of which is to stimulate and properly develop certain intestinal bacteria (bifidobacteria), in particular to allow the digestion of fibres and other composite matter not assimilable by humans and/or animals. By increasing beneficial microbial populations, the said prebiotics act indirectly on the processes of chelation and mineral assimilation and also participate in making the immune system function properly.
Their application in plant production
Prebiotics stimulate beneficial bacteria present naturally in the environment. These molecules are just as capable of stimulating the intestinal microflora as of dynamically activating other bacterial populations and especially those that develop in agricultural soils.
Phytostimulating rhizosphere bacteria, closely linked to rhizogenesis in sown crops, can thus be activated by the use of prebiotics applied to the soil.
A ground-breaking company in the development of prebiotics used for plant production, LALLEMAND PLANT CARE markets various yeast derivatives designed to carry out this function in soils and other substrates.