3. For agriculture, weed control is a matter of survival
World agriculture has always been severely handicapped by “weeds”, called “weeds” by professionals. Indeed, all unwanted plants are not bad, some are even downright useful. And besides, who are we to declare that a plant is intrinsically bad, and on what criteria?
Controlling them, and if possible eradicating them, has become an obsession of peasants for millennia. Difficult objective to achieve because they are particularly resistant plants, which have been able to cope with diseases, droughts, heat waves, floods, freezes, animal attacks, etc. But also to move with the wind, animals, men, mechanical transport. And even adapt to changes in species cultivated by “Vavilovian mimicry”.
In fact, these wild plants seem to be better adapted to environments than cultivated plants. Many strategies have therefore been put in place over the ages:
A. We tried to burn with stubble after harvest. This ancestral practice is now banned in Europe because of its many drawbacks: loss of carbon and nitrogen useful for soil fertility, pollution, emission of fine particles and greenhouse gases, fire hazards, etc. However, it should be noted that it continues to be used elsewhere for cereals, and, very unfortunately, systemically and on a massive scale to clear forests in many tropical countries, starting with the Amazon and tropical Africa.
B. The most widely used method has been to bury via plowing. It has been widely proven, to such an extent that farmers have long been called “plowmen”. This practice exploded with the appearance of the tractor and cheap oil after World War II.
Indeed, if we risk sowing in soil in which viable weeds are already growing, the latter will enter into strong competition with the emerging crop. It is still easier to destroy them before, even if it requires a lot of work, human, then animal and now mechanical.
In the XV e century, plowing was commonly practiced in France, judging by the ” Very rich hours of the Duke of Berry “. In the following century Sully considered him to be one of the “two breasts of France”.
Let us remember that in the 1950s, a third of the French agricultural surface was devoted to producing fodder for millions of draft animals, oxen and horses! Today, there are more than a million tractors in France, with powers that are usually counted in hundreds of horses.
But this activity is becoming more and more problematic. Including for the elimination of weeds, because the majority do not die in one year, and are therefore brought to the surface, fresh and ready, by plowing the following year (annoying, when we have consumed 15 to 40 liters of fuel per hectare to stir up the earth).
In addition, this increasingly deep plowing brings up the pebbles, destroying earthworms, fungal filaments and bacteria. They compact the earth, cause erosion and beating (raindrops form an impermeable layer on the ground) and reduce the bearing capacity of the soil (the machines get stuck in the fields).
They expose the remains of nitrogenous fertilizers to the winds of autumn and transform them into nitrogen pentoxide, which has a global warming power 298 times greater than carbon dioxide. Last but not least, plowed fields only use solar energy 6 months a year. The rest of the time, no photosynthesis. We now know better how harmful plowing is for the planet and we are trying to limit it as much as possible, or even eliminate it.
C. This is to say if the appearance of chemical herbicides was experienced as a blessing: we could finally poison weeds, at low cost. The profession has massively engulfed this path. Especially at the beginning, when these plants had not yet developed resistance, which is no longer the case (bromine, ryegrass, poppy, matricaria, wild oats, lamb’s quarters, etc. are more and more problematic. ).
We must realize that the notion of 100% does not exist in biology : when you apply a herbicide, you are happy when you have eliminated 98% of the weeds. But the remaining 2% have managed to survive and have plenty of room to reproduce. Over several generations, careful selection of herbicide resistant varieties has been achieved, and usually a change in molecule or method is required.
Note that, contrary to a widely held opinion in the population, it is not only conventional farmers who use chemicals. Organic farmers certainly use much less herbicides (because they are only entitled to natural products deemed to be biodegradable), but they use, and sometimes abuse, fungicides and insecticides.
In fact, glyphosate is only the 2nd most used chemical in France in 2019 with its 6,000 tonnes. It is far exceeded by sulfur, which has been used, especially by bios, at over 11,000 tonnes (plus the 500 tonnes of copper sulphate, a product that is in no way natural). We can also mention 2 insecticides very popular with organic people: petrolatum oil (2,300 tonnes) and rapeseed oil (1,700 tonnes).
The arrival of glyphosate in France at the end of the 1970s was therefore greeted with real relief: as it is total, foliar and systemic and that it degrades relatively quickly in soils (not in an aquatic environment), it makes possible a semi in the hours or days following its application.
It has replaced many more dangerous, less effective and significantly more expensive products, most of which have since been banned. We have even gone so far as to create GMOs specially adapted to resist it, and which therefore allow its spreading during cultivation, and not just before cultivation. In particular the famous soybean “Roundup ready”, which currently represents 84% of the world harvest..
It was one of the major reasons for the considerable increase in productivity which was observed in France between the 1960s and the 1990s, with a tripling of wheat yields (which went from 25 to 75 quintals per hectare). ).
Note that it remains essential for farmers who have decided to stop plowing: those in soil conservation agriculture, who cultivate their soils 365 days a year, thus considerably improving their capture of atmospheric carbon as well as fertility and the natural biodiversity of the land thus cultivated.
This is also one of the reasons explicitly put forward by the Ministry of Agriculture to postpone the ban date for glyphosate. The others being that one cannot take more restrictive measures in a single country of Europe under penalty of strong distortion of competition. Not to mention the lack of solutions in a certain number of productions and the difficulty of implementing partial bans.
We are here in front of a cruel dilemma:
Is it better to warm the planet, reduce biodiversity and soil fertility, and ultimately apply a lot of fertilizer while plowing, or risk polluting soils and groundwater by using chemical herbicides?
But little by little, the defenders of the environment and of health gradually became numerous, motivated and… noisy, and they preferred to choose to fight on the ground of chemistry than that of plowing. It must be recognized that they are now close to winning their fight.