Introduction to integrated methods in the vegetable garden
The different phases of hot composting
Chapter : Crop soil
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⇒ The different phases of hot composting
Introduction to integrated methods in the vegetable garden
Chapter : Crop soil
Previous or next articles ; click on a title to go to the page
⇒ The different phases of hot composting
This phase consists of gradually gathering organic matter without trying to precipitate the fermentation. No materials that accelerate fermentation are added, nor is water added. In many cases, low temperature fermentation cannot be avoided and will be more or less active depending on the moisture content of the bioresidue. This storage period corresponds to the mesophilic phase described in books and websites on composting. Without the addition of nitrogen (urea or ammonium nitrate) but with the addition of water, this first stage of composting is considered to be an initial phase of composting characterised by a gradual rise in temperature of up to 30 to 40°C.
During this low-temperature phase, and if the humidity is sufficient, the organic matter is invaded by mesophilic micro-organisms. Bacteria and fungi will start to break down and digest the tough debris. These micro-organisms absorb the simple molecules (sugars, alcohol, amino acids, etc.) and begin to break down the more complex molecules (cellulose, proteins, starch, etc.), producing a significant release of CO². If this mesophilic phase lasts several months, the compost is colonised by macro-organisms that participate in the decomposition process by feeding on organic matter rich in proteins, sugars and fats.
The mesophilic phase is not necessary for the next phase described below. This is especially true since it is important to avoid wasting high-energy materials that will be useful in the thermophilic phase.
This is an active fermentation phase where the temperature in the centre of the pile must reach at least 55°/65°. In some industrial composters where air is blown in, the temperature can easily reach 70°. An 800 litre family compost with a lot of lawn clippings can reach this temperature. If there is not enough lawn clippings or if the gardener cannot get hold of dried blood, guano or other nitrogen-rich organic material, mineral nitrogen (urea or ammonium nitrate) must be added to reach 55°. For those who can compost in large piles (several m³), the temperature can reach 75-80° when the substrate is rich in highly putrescible materials such as sugar and starch. However, we try not to exceed 70° so as not to disadvantage composting.
Before starting the thermophilic phase, as far as possible, earthworms that do not appreciate temperatures above 35° (mainly highly coloured epigees that reproduce very quickly in composts) and cetonia aurata larvae should be removed from the compost and placed in a container with potting soil. Compost is frequented by other beneficial insects such as sowbugs, lules (julida), millipedes, earwigs and hermitia larvae (black soldier flies), which in principle leave the compost to take shelter elsewhere as soon as the temperature rises above 35°C. It should be noted that the woodlouse, although it sometimes has a bad reputation, plays an important role in the early stages of the decomposition of organic matter, provided that the environment is sufficiently humid.
If the substrate contains sufficient highly putrescible organic matter, the addition of pearl urea or ammonium nitrate, seeded with mature compost residue, produces a very rapid temperature rise in one or two days. Thus, this process saves time by avoiding the mesophilic phase.
Deposition of thermophilic microorganisms in the centre of compost where the temperature has exceeded 65°C
Initially, the organic matter is decomposed by an army of actinomycetes (a) and then thermophilic bacteria, mainly archaebacteria which become predominant, but also fungi (Rhizomucor pusillus, Rhizopus microsporus, Aspergillus fumigarus). On the other hand, mesophilic micro-organisms disappear. During this phase, composting consumes a lot of oxygen and water and produces gases (CO², methane, etc.). It is also necessary to water it from time to time, especially in summer, in order to maintain a constant humidity without the compost becoming waterlogged.
When the temperature of the compost falls below 35°, a new mesophilic phase takes over until the temperature of the compost corresponds to the outside temperature. The beneficial organisms previously placed in a holding tank are returned to the compost. The mesophilic flora finishes degrading the last polymers left intact after the thermophilic phase. Part of the humus is made during this phase by incorporating the remaining nitrogen into complex molecules. Moisture control is still important throughout the process. In contrast to the previous phase, the addition of a nitrogen fertiliser does not produce a rise in temperature, which shows that the thermophilic phase has been completed. The added nitrogen is not lost, as it is integrated into the humus formation process. All plant debris with little lignocellulosic material should disappear (except for the toughest which should be sorted).
It is common that during this cooling phase, the macro-organism population is slow to colonise the compost if the amateur gardener has not previously stocked up on these macro-organisms. This is not dramatic, because it is mainly the mesophilic microbial flora that quickly takes over. This can be easily seen from a microscopic examination of a sample.
The cooling phase itself is prolonged by a more or less long period corresponding to the humification work of useful auxiliaries specialised in the decomposition of tough cellulose materials. These include sowbugs and especially the larvae of the woodlouse. In general, it does not take long for these beneficial organisms to colonise a compost, and the colonies grow stronger every year as long as the gardener maintains at least one compost in the cooling phase. A colony of several hundred keton beetle larvae is particularly effective in reducing to their simplest form organic residues that would have resisted the thermophilic phase. These larvae can be collected and housed in a container of compost over the winter (or left in a composter all winter); the adults will not leave the site in the spring and will lay their eggs in the compost. After 2 to 3 years, you will end up with an abundant colony of keton larvae that can easily be maintained by periodic additions of compost from a thermophilic phase and from another composter.
The cooling phase itself is prolonged by a more or less long period corresponding to the humification work of useful auxiliaries specialised in the decomposition of tough cellulose materials. These include Epigeic, Woodlouse and especially the larvae of the cetonia aurata. In general, it does not take long for these beneficial organisms to colonise a compost, and the colonies cetonia aurata every year as long as the gardener maintains at least one compost in the cooling phase. A colony of several hundred keton beetle larvae is particularly effective in reducing to their simplest form organic residues that would have resisted the thermophilic phase. These larvae can be collected and housed in a container of compost over the winter (or left in a composter all winter); the adults will not leave the site in the spring and will lay their eggs in the compost. After 2 to 3 years, you will end up with an abundant colony of keton larvae that can easily be maintained by periodic additions of compost from a thermophilic phase and from another composter.
For small compost bins, it is preferable to start composting at the beginning of the summer to benefit from the ambient heat. In Provence and during the summer season, watering should be done every 1 to 2 days. A 1m³ compost in thermophilic phase consumes at least 10 to 15 litres of water every day.
For private individuals, urea is very suitable for increasing the nitrogen dose. Urea is dissolved in a watering can containing about 10 litres of water. This solution is poured onto the surface of the compost. Pearl urea is available from agricultural cooperatives. But this urea is only available in 50 kg bags. You will then have a reserve of mineral nitrogen for at least 10 years, bearing in mind that this mineral fertiliser will also be used to meet the high nitrogen demands of your vegetables at a certain point in their development cycle.
The temperature rise to 55/65° can be measured with a laboratory thermometer. This measurement should be taken 20/25 cm from the edge of the compost. The destruction of all pathogens is only possible if all the elements of the compost are subjected to a temperature of 55/65° for at least 15 days. This requires frequent turning to ensure even treatment ( ) (1). It is imperative that the waste of certain plants be subjected to this heat treatment, such as melon stems and leaves, which may contain fusarium sports, or when tomato remains contain alternaria spores or didymella lycopersici (black foot).
During composting in a pile, the tougher debris is placed in the centre and covered with finer debris followed by watering. The thermophilic phase should last at least one month, but it will be more effective if it lasts longer with successive additions of highly fermentable material and nitrogen. For this purpose and in case of a break in the highly fermentable organic material, one can use a bag of low quality flour for one m³ of compost, which is not very expensive for a private individual.
Tip
Lawn clippings are also an interesting source of nitrogen. The difficulty is to have a sufficiently large stock of grass when you decide to launch a thermophilic phase for more than 1 m³ of structuring organic matter. It is not advisable to store freshly mown grass in bags, as this grass contains a lot of water and a fermentation process will take place, producing toxic substances and bad odours. The grass should be bagged after drying in the sun for several days. The final dry product should look like hay.
Actinomycetes are not fungi, but bacteria with a diverse morphology; spherical in shape or gathered in rudimentary or highly branched filaments. Throughout their life cycle, Actinomycetes can combine these different forms. The filaments grow from the germ that gave rise to them to create a radiating structure resembling fungal hyphae. Actinomycetes multiply less rapidly than other bacteria.
Affinage à l’aide d’un tamis
This phase consists of removing foreign elements (stones, pieces of metal or plastic, etc.) and insufficiently decomposed elements such as pieces of wood from hedge shredding with a sieve. The earthworms and other beneficial organisms must be recovered and placed in another compost in the mesophilic phase. The tough debris is transferred to a younger compost, or spread on the surface of the cultivation area to form a layer that will evolve according to the principles of RFW (Rameal Fragmented Wood) (2)). This debris will therefore continue to decompose on site, sometimes for several years, which helps to neutralise humus losses and to feed useful auxiliaries.
The product of the refining phase can be spread on the soil if the next crops accept it (especially to be avoided for liliaceous plants...), or stored to engage in the next phase of maturation.
It is preferable to use a sieve with a 3 mm mesh. The slightly moist organic matter must be forced through the mesh with a hand protected by a gardening glove, which at the same time reduces the last large organic debris (compacted decomposed grass, pieces of straw or decomposed branches, etc.) to fine particles. Fouling of the mesh is the result of excessively wet or unfinished compost.
a) Cultivation technique invented in Canada. Shredded branches, mainly from hardwood trees, are deposited on the soil surface in an attempt to replenish the surface litter of forests. Fungi play an important role in the degradation of organic matter due to the presence of atmospheric oxygen.
The final product is stored in an aerated area for at least 3 months and will continue to develop. Some of the elements such as nitrogen, phosphorus and potassium consumed by the microflora for its own development return to the compost in a form that can be assimilated by plants or participate in the formation of more complex compounds. During this phase, the organic matter is reorganised into more stable compounds to form humus. At the end of this maturation phase, the compost should not contain any organic matter that is easily degradable by micro-organisms. After spreading, this compost continues to evolve to form agricultural humus and then CAC with clay.
At the beginning of the maturation phase, the pH of a family compost can be between 8 and 9. It should not be acidified as this can lead to odour problems and loss of nitrogen. Compost rich in woody waste requires a maturation phase of 4 to 6 months.
Iules (Julida)
the larvae of cetonia aurata
Woodlouse
Black soldier fly
Chrysalid of cetonia aurata surrounded by a cocoon of plant debris, collected in a compost
Two species of cetonia collected in a compost
The Mediterranean region is known for the diversity of its woodlice, which can be found in forests, meadows and all places where organic matter accumulates. Sowbugs are crustaceans that develop symbiotic relationships with bacteria that produce cellulases in their intestines to break down tough woody material. It is therefore interesting to keep these small crustaceans even though they are known to attack certain crops such as strawberries.
Very common in mesophilic composts as soon as vegetable and fruit remains are deposited. These maggots develop very quickly and their digestate contributes to the transformation of organic matter.
This larva is frequently found in composts. It is often confused with the cockchafer larva, which is never found in composts. The females lay eggs in summer and the larvae develop for more than a year in a compost. Several generations of larvae can therefore be found. The adults feed on nectar and pollen from flowers. These larvae and chrysalises must be removed from a compost before the thermophilic phase, as they cannot withstand the rise in temperature and the gases produced during this composting phase. Larvae will attempt to rise to the surface and may be found dead on top of the compost.
Like the larvae of hermitia illucens, the larvae of cetonia aurata on decomposing organic matter. In summer, after the thermophilic phase, females come and lay eggs in the compost which hatch quickly enough to produce larvae. Their development can be very rapid and it is not uncommon for a compost to contain hundreds of larvae which will then significantly accelerate the final decomposition of the organic matter. Tough particles are attacked by these larvae. Their excrement is quite easily identifiable in the form of small elongated droppings of 1 to 2 mm. The larvae start by attacking the surface layers of compost, leaving behind their excrement, which accumulates where the larvae have taken up residence. These droppings are collected for use in the maturation phase of the compost.
Some pathogens are difficult to neutralise during hot composting of contaminated plant residues. Their elimination is possible if the temperature is constant throughout the compost mass over several days. However, this situation is rarely achieved, as the temperature is not homogeneous in the compost, especially at the edges where there is a loss of heat. The best known pathogens are :
The vessels of the plants are invaded by a very common soil-borne fungus (Fusarium oxysporum) resulting in a wilting of the plant which dies quickly. All vegetables can be affected, in particular: tomatoes, melons, cucumbers, courgettes, onions, potatoes, celery, etc. This type of fungus is divided into several varieties. For example, for tomatoes, according to the ESIAB website, "a distinction is made between Fusarium oxysporum f. sp. radicis lycopersici, which attacks the root parts, and Fusarium oxysporum f. sp. lycopersici, which attacks the aerial parts of the plant". According to some researchers (Mercedes Castejón-Muñoz G. J. Bollen), Fusarium oxysporum would be destroyed if a temperature of 55° throughout the compost is maintained for 30 minutes (2) with a survival rate of only 0.001% of propagules (a). Any invasive wilting seen on tomato in hot weather is likely to be the result of a fusarium attack. As it is not always easy to diagnose Fusarium, some professional gardeners avoid cold composting wilted stems and leaves as a precaution. When burned, this waste is safe and can be put into compost, which recovers mineral salts such as potash and phosphates (incineration in residential areas; see local regulations).
This fungal disease caused by Plasmodiophora brassicae mainly affects cabbage crops. Cauliflower and broccoli are particularly susceptible. The disease manifests itself by the appearance of growths on the roots and the crown, causing the plant to die back. According to some authors, the fungus is destroyed with a temperature of 55° in the whole compost for at least 96 hours.
This disease is caused by the fungus Olpidium brassicae which can also affect tomato roots and lettuce. This fungus also carries a phytovirus. Olpidium brassicae is not destroyed after thermophilic composting at a temperature of 50 to 70° for 2 to 3 weeks followed by a maturation phase of 5 months (2).
This disease is caused by the telluric fungus Pyrenochaeta lycopersici, which occurs in so-called "tired" soils that have received successive tomato crops. There are several strains corresponding to the temperature of the soil. The destruction of this fungus requires a temperature of around 73° C (3).
in principle, rhizoctones should not be a problem if the composting is well conducted and especially if all elements undergo a thermophilic phase. The addition of nitrogen as a degradation activator on potato and beetroot residues is known to favour the disappearance of brown rhizoctone (4). However, it only takes a few leftover potato, tomato, celery, cabbage or carrot peelings that have escaped a thermophilic phase for this fungal infection to spread to new crops. In case of doubt, it is best to burn the crop residues.
a) propagules: structures for dissemination and reproduction such as spores
Notes :
- The genus Fusarium belongs to a group of fungi called Soil-borne plant pathogenic fungi (SPPF), to which also belongs verticullium, responsible for severe and relatively frequent attacks on some vegetable crops such as celery, tomatoes, aubergines, potatoes .... SPPFs produce survival structures such as thick-walled chlamydospores or very resistant sclerotia that can survive several years in the soil. PFAS are grouped into two functional categories: soil inhabitants and soil invaders. The first category generally includes non-specialised fungi that infect seedlings and young roots, while the second category includes pathogens that show a degree of host specificity. High humidity accentuated by low temperatures is often responsible for fungal infection. However, some fungi tolerate lower water levels and prefer warmer soils (25 to 35°C).
- Calcium cyanamide destroys all microorganisms, both good and bad, and should be used sparingly if it is to be used to compost plant waste infected with resistant pathogenic microorganisms.
For soils that are too rich in limestone or sand, here is a recipe for a clay-humus amendment. At the beginning of the maturation phase, the compost is enriched with clay in this way:
The principle is to mix compost with clay or marl (containing about 50% clay) to facilitate the formation of clay-humus complexes. Clay or marl should be finely ground after passing through a sieve (mesh size about 2 mm) to remove unnecessary sand grains. Marl contains sufficient limestone for CAC to form.
Clay-humus amendment
The preparation of clay-humus amendments requires the presence of limestone to stabilise the clay-humus complexes. For commercially purchased clays, a vinegar test should be used to check whether the clay contains limestone. To do this, a few drops of vinegar are poured onto a sample of a few cm³ of clay, which should produce foam if the clay contains limestone. The proportions of the mixture depend on the clay content of the marl. The proportions are approximately one volume of marl to 5 to 10 volumes of compost for marl containing 50% clay. For a very calcareous soil, this amendment can contain up to 1/3 clay. This mixture is kept slightly moist throughout the maturation phase.
Many vegetable plants cannot tolerate a recent addition of compost and even less so the burial of more or less well decomposed manure. The presence of organic matter increases the risk of fungal diseases. This is particularly the case for garlic, cucurbits and tomatoes. It is therefore preferable to incorporate the compost into the garden soil during the autumn by means of a pseudo-ploughing operation for the beds that will receive these crops. For plants that can withstand a recent application of compost, it is incorporated into the garden soil in early spring. For garlics and tomatoes, you will have even fewer problems if the compost was incorporated a year ago. In this case, a spring stockpile of mineral fertiliser only should be used.
1) Guide du traitement des déchets ; réglementation et choix des procédés – Alain Damien
2) Induction of heat resistance in Fusarium oxysporum and Verticillium dahliae caused by exposure to sublethal heat treatments
3) I G. J. Bollen et all. 1989 inactivation of soil-borne plant pathogens during small-scale composting of crop residues
4) G.J. Bollen, 1984. The fate of plant pathogens during composting of crop residues - Composting of agricultural and other wastes / Gasser, J.K.R., - p. 282 - 290.
5) La technique betteravière – bien gérer le rhizoctone brun N°1007 16-9-2014
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