AGROECOLOGY (THE SOIL) - DECONTAMINATION POTENTIAL
In the early 1990s, a Swedish farmer, Göran Olsson, concerned about the risks of environmental consequences of his agricultural practices, had the idea of confining his phytosanitary effluents in a sort of pit filled with soil and organic matter. His idea was to avoid pollution around his filling and washing point, assuming that the effluents, over time, would lose all or part of their contaminating potential.
Phytosanitary effluents are constituted by water, contaminated with synthetic or natural pesticides, spattered during the filling of spraying machines, rests of the tanks which the pump can't aspirate, residues of mixtures unapplied to the crop, and especially contaminated water generated by the washing of spraying machines after the applications. Washing water generally accounts for nearly 90% of total phytosanitary effluents.
It may also happen, although exceptionally, that during the preparation of a tank, a chemical reaction (due to the quality of the water, to the temperature, or to the mixture of products) occurs, or just an error (incorrect pouring into the tank of an unsuitable or prohibited product), which makes the phytosanitary mixture unusable. In this case, this failed mixture is also a phytosanitary effluent.
I imagine that several attempts have been necessary to get a coherent result, but the fact is there. This gentleman thus invented a principle, called biological bed, or biobed, then scientifically studied and modified to improve its efficiency, which allows the farmer to considerably reduce the collateral effects of phytosanitary sprayings. The agrochemical giant Bayer proposes an optimization of the principle under the brand Bayer Phytobac®, increasingly known in agricultural circles. It's an improved biobed that reduces the volume and ensures an optimal operation.
Pesticides, if concentrated in excessive amounts, are potentially hazardous to the environment.
This is true for synthetic pesticides, although the molecules currently available in Europe present a very low risk, compared to the many molecules prohibited in recent years.
This is also true for "natural" pesticides authorized in organic farming. Indeed, many of these pesticides are plant extracts or products synthesized from bacteria and are ultimately chemical molecules that have similar environmental effects to synthetic pesticides (risk to soils, to aquatic fauna, to birds, etc.). About that point, see my series "Natural vs synthetic" https://culturagriculture.blogspot.com.es/search/label/EN-%20Natural%20vs%20synthetic, of which at the moment I published three chapters.
It is therefore very important that, irrespective of the method of cultivation adopted, apart from biodynamic agriculture, the effluents are properly controlled.
Many farmers, who are concerned about this problem but have no effective available system, have taken steps to prevent their phytosanitary effluents become a pollution source. Many farms have a pit in which they are stored and confined, pending evaporation, or spreading, after dilution in water, to uncultivated areas and away from water points (wells, streams, ponds, basins, etc.). But this method has limits. It's nevertheless better than not doing anything, and looking elsewhere ...
For several years, the recognition of biobed and Phytobac® remained limited to a few farmers, without actually spreading. But in 2007, in France, several political meetings were held, called "Grenelle Environnement", in order to make decisions directly affecting the environmental consequences of different human activities. These meetings gave rise to legislations, standards of operation for all economic sectors. As far as agriculture was concerned, it was the start of a whole series of inventions and standardizations concerning in particular the uses of pesticides and fertilizers, natural or synthetic.
The principle of the biobed thus marked its great takeoff. At present, several thousand biobeds are operating in France, and nearly twenty principles for the destruction of agricultural phytosanitary effluents have been authorized by the Ministry of Agriculture. But a single principle can be considered biological, biobed, and specifically Phytobac®. All other principles lead to a contaminated residue (filters, sludge, bags, etc.), the collection of which must be carried out with all the necessary precautions, to a specialized company, for its reprocessing.
The biobed makes it possible to carry out the decontamination treatment locally, without danger, without transport, incineration or industrial process.
What science demonstrated, in particular the INRA (National Institute for Agronomic Research) in France, which has extensively worked on the principle of biobed to verify its validity, is that chemical molecules, whether synthetic or not, are naturally decomposed by the bacterial flora of the soil, bringing them back to simple elements or to simple molecules, non-polluting, naturally present in the environment, such as water, carbon dioxide, or calcium carbonate. This process takes time (on the order of 4 to 6 months), but is real and complete. Only a few very rare molecules, currently banned, resist this process, especially DDT. The complete degradation of DDT in soils takes several decades, going through several phases, DDD and DDE.
But all the present molecules are completely degraded in the soil within a few hours to a few months. This is one of the criteria that the competent authorities currently consider essential to accept the approval of a new molecule, or the renewal of an old one.
How is a biobed made?
In the original Swedish system, the washing area is simply a pit filled with soil and organic matter in which the effluents fall and are stored. Nature does its work, the grass grows and participates in the efficiency of the system. However, large farms must have large areas, complex and expensive facilities, and maintenance is very difficult. Furthermore, the risks of overflowing are high.
The optimized Phytobac® uses the same idea, but incorporates a number of criteria to increase its efficiency, while reducing its volume, facilitating maintenance and increasing its safety.
The effluent thus passes through a totally impermeable washing area, is stored in a reservoir, and is applied to the degradation/evaporation container by a set of pumps. The depth of the substrate is limited because the aerobic useful microbial flora (which needs air) is maintained in the first 50 centimeters deep only.
In short, the principle is the same, but the implementation is different, to improve its effectiveness, safety and control.
How does the soil decompose these molecules?
In fact, it is the soil bacteria that do it. They attack the molecules directly and decompose them by breaking the chemical bonds between the different atoms.
Agrochemical molecules are all composed of very common elements, C, H, O, N, Ca, Cl, S, K, Cu, Fe, F, P, Zn, Mg, Mn, which are all naturally present in soils elements and are almost all nutritional elements for plants. What chemistry does is to combine these elements together, with special connections, to make molecules for specific use.
These elements, once released from the bonds that make them a molecule, will recombine to form other ordinary molecules, such as water, carbon dioxide, and calcium carbonate.
Some elements, especially metals, remain in the biobed. Therefore, concentrations of these metals in the substrate must be monitored to avoid contamination of the biobed. When these concentrations approach the levels considered dangerous (according to in force soil pollution standards), the substrate is renewed. The old substrate, which is non-toxic if the standards are met, i.e. if it's renewed before reaching the maximum permissible level of metals, is spread on the farm over a large area, in a way to further dilute the presence of these metals.
To give you an idea, the substrate of a Phytobac®, studied for about 50 hectares of orchards, will represent about 3 tons of soil. It is considered that a maximum of 10 tons of substrate per hectare can be applied. The weight of agricultural soil (the first 60 centimeters deep) represents about 10,000 tons per hectare.
The substrate should not exceed 50 mg of copper per kg of soil. Distributed and mixed over 1 hectare, the concentration is reduced 1000 times, with negligible results, since they are below the natural levels of these elements in most soils.
On average, the substrate will be renewed every 5 to 10 years, especially depending on the use of copper and zinc, the most used in agriculture metals, both conventional and biological, because they are natural elements. Both are powerful fungicides, bactericides, and important nutritional elements.
However, their excess is toxic, both for plants, fauna, soil microfauna and microflora.
In order to promote bacterial activity, care must be taken to aerate the substrate once or twice a year, by incorporating straw or other lignin-rich organic material, which will serve as a basic feed for the bacteria.
It is therefore a biological method of decomposition of chemical materials, which makes possible, through good agricultural practice, to avoid to the maximum the collateral effects of phytosanitary sprayings, in both conventional and organic agriculture.
It is also a characteristic of soils, to be able to break down chemical molecules. Soils that are chemically polluted are very rarely agricultural soils. Only DDT and some other organochlorines or residual herbicides, banned for a long time, resist degradation. They are still found in many soils, more than 40 years after they were banned, but in extremely low levels. The degradation takes place, but it's very slow.
Cases of pollution are generally due to accidents, and are therefore very punctual, or to industrial or mining pollution.
On agricultural farms, only the proximity of the washing and filling points can present significant pollution, but on very small surfaces.
However, the risks of pollution of surface and groundwater remain relatively high due to rainfall, in particular of effluents accumulated near these critical points.
We now have the opportunity to avoid unintentional soil and water pollution due to the use of natural or synthetic pesticides.
This is undoubtedly an important step forward for the sustainability of agriculture and to avoid as far as possible the undesirable effects of crop protection.
The concern of users is growing, but often not yet to the point of measuring the interest of investment in this kind of equipment.
Yet the public's concern grows enormously, not always in a justified or even reasonable way, under the pressure of certain groups of pressure of which I have already widely spoken.
But this concern, even if it is largely exaggerated, must represent an engine of evolution and innovation.
However, we are surprised by the lack of interest on the part of government departments in this kind of progress.
Everyone is scandalized by pollution of all types, or by the risks that may arise from the use of pesticides, natural or synthetic, but administrations are reluctant to take drastic decisions on the subject. The treatment of effluents is only really taken into account in two or three countries, particularly in France. Yet, even in France, it's not compulsory. This is a strong recommendation supported by investment aid. Moreover, it takes into account only the risks of surface and groundwater pollution, not soils.
Some supermarket groups, or quality protocols, are beginning to worry about them, but again, there is no obligation on the subject today. Only accidents are punished.
Would it not be smarter and more effective to make the control and treatment of plant-protection effluents mandatory, in order to avoid accidents, the consequences of which are always serious?
The soil, through its microbial life, has the capacity to protect itself by decomposing the molecules likely to be harmful to it. It is this characteristic that the biobed uses. A careful use of modern pesticides does not pose a risk to soils, if properly managed. The natural microbial life in all soils is normally sufficient to degrade all currently available molecules, provided that the agricultural practices allow a good aeration of the superficial layers.
However, attention must be paid in at least two particular situations:
- Very sandy soils generally have low or no microbial life. The use of pesticides must be extremely precautionary. It's all the more true that these soils have little capacity to retain molecules, which are likely to reach quickly the groundwater, without having had time to be decomposed.
- Crops or cultivation methods which use metallic salts in large quantities. This is the case of certain crops such as vineyards or olive trees. This is also the case for organic farming, which, because it lacks the diversity of synthetic fungicides, uses copper and zinc salts repeatedly. Metals that are not degradable can accumulate to dangerous levels.
The use of natural or synthetic pesticides is a useful, safe, and even ecological practice thanks to the productivity it allows in food production. But to be sustainable, it's essential to take a series of precautions such as control of phytosanitary effluents.
The soil itself provides us with the solution to meet this need, thanks to the biobed.
Soil is an indispensable, living and fragile resource.
It's our duty as users, farmers, gardeners and others to take great care of them. It's also necessary to understand its functioning in order to make the best use of it without harming it.
Knowing your soil is essential for a sustainable agriculture.
Agronomy is a science that still has great things to discover.
Some even believe that this is one of the main explorations that humans still have to realize.
The future of humanity lies beneath our feet, let's take great care of our soil.