Soil fertility: is the apocalypse coming tomorrow?

A look back at an old theory of apocalypse in agriculture

According to a report broadcast on France 2 on 31 January 2016 entitled “Les soigneurs de terre” (1) (The Earth Healers), which gave prominence to the theories of Claude Bourguignon, a former agronomist at INRA, the soil cultivated in France will soon be unable to feed us. In this report, we are promised a catastrophic future. In temperate zones, the harmful effects of ploughing are said to be gradual and even go unnoticed. However, for several years now, conventional agricultural production has remained at optimal levels. So how can this imminent catastrophe be explained?

Crops are boosted by mineral fertilisers and tillage, giving the impression of improved fertilisation, but in reality the results obtained are misleading, as the soil becomes depleted due to the scarcity of humus. Both farmers and consumers are victims of lies. Today’s agriculture is destroying the earth. It serves to fatten a system at the expense of life. Conventional agriculture consists of keeping plants alive in dead soils that, without pesticides and fertilisers, are doomed to disappear. Agricultural soils are depleted by the widespread use of intensive farming, and the last remaining good soils are dwindling away. Analyses of certain soils have shown that their fertility is comparable to that of the Sahara. France is in danger, threatened with being covered in infertile fields within the next quarter of a century.

Soil cultivation is also practised by amateur gardeners using rotary hoes or spades, and they sometimes use mineral fertilisers. We can therefore conclude that these amateur gardeners are also responsible for the degradation of cultivated soils. Have they really noticed this? Is this apocalyptic vision realistic?

Variation in organic carbon content in France between the periods 1995–1999 and 2000–2004 by county

If ploughed soil is truly dead and incapable of performing its biological functions, this can easily be demonstrated by a simple experiment using three jars, soil samples and urea pellets used as fertiliser in agriculture. This experiment is described at the end of this article.

Almost a century ago, Sir Albert Howard believed that soils were becoming depleted, and 80 years later, this argument has been taken up by all those who are convinced that modern agriculture is destroying the planet. Ultimately, this is nothing new, but rather the repetition of an old theory.

With regard to the consequences of tillage, what about carbon losses from cultivated soils in France?

Between 1995-1999 and 2000-2004, the organic carbon content of soils decreased in 21.4% of cantons in mainland France, mainly in areas of intensive farming where cereal monoculture predominates (particularly the Paris basin and northern France). Conversely, the organic carbon content of soils is stable or increasing in 48% of cantons (including a 10% increase) (2). The situation in France is therefore not so dramatic, even if it is necessary to review certain agricultural practices in areas of intensive farming.

Crops in stony or desert areas that produce humus

When agricultural practices are carried out properly, including the use of synthetic fertilisers and even ploughing, there are many examples that demonstrate that the soil can be enriched with humus, even when its original structure is poor:

In the Asse Valley, located in the Alpes de Haute-Provence department, cereals are grown on poor soil saturated with gravel and pebbles, as shown in the photo on the left.

In the El Oued region of Algeria, crops are grown in circular fields in the middle of the desert. The wilaya of El Oued ranks first among the wilayas of southern Algeria in terms of agricultural production, particularly early vegetables, dates, cereals, potatoes, peanuts and market gardening. Successive crops of wheat and potatoes are accompanied by an increase in soil carbon content (largely due to the stubble left in place after wheat cultivation) (3).

Si vous survolez le désert d’Arabie, vous constaterez que ce désert est également parsemé d’énormes champs circulaires recouverts de blé.

There are no regions more infertile than these arid deserts of Africa. And yet, farmers manage to grow cereals and vegetables there. How can soil saturated with stones or sand be enriched with humus when mineral fertilisers are added? Quite simply through the decomposition of organic matter from roots and rootlets, and through the development of microbial biomass following the exudates synthesised by plants to nourish the rhizosphere (see description of the mechanism here). The rest is provided by crop residues.

After a harvest, anyone can easily see with a spade that cultivated soil has been enriched with organic matter from roots that remain in the soil for a few weeks to a few months (depending on the type of crop) before being decomposed by microflora. It can also be seen that at a depth of 20 to 30 cm, earthworms thrive on crop residues even if the soil has been tilled and fertilised with synthetic fertilisers. The earthworm population is even greater when cover crops are used between harvests or when the soil has been fertilised with manure and/or compost.

The wriggling of an earthworm that excites a minister

In France 2’s report on 31 January 2016, a farmer from the Sarthe region who has converted to no-till organic farming presents a clump of soil taken from a field covered with cover crops. A worm wriggles in the clod of earth, which Stéphane Le Foll, former Minister of Agriculture, Agri-Food and Forestry, hastens to pick up. The same demonstration could just as easily be carried out on land that has been properly cultivated using traditional methods, especially when there is sufficient moisture and it is not during a heatwave (which forces earthworms to burrow deep into the soil to protect themselves from the heat). Gardeners and market gardeners who have never seen their cultivated plots turn into deserts must have had a good laugh watching this TV programme. It is clear that this programme is not aimed at them. It is mainly aimed at the majority of French people who live in large cities and have no experience in agriculture, and the few followers of various unscientific agroecology sects who are prepared to swallow anything.

In the France 2 report, we learn that in a farming system characterised by the use of plant cover and no tillage, it takes at least 5 years to restructure the soil and 10 to 15 years to regain acceptable yields. However, there are other methods that are just as effective and much faster, such as spreading compost made from waste from a crop and livestock farm, on-site straw shredding, and burying plant cover made from intercropping. It is also necessary to accurately estimate the actual loss of humus each year, which depends on several factors such as climate, soil structure, the method and frequency of tillage, the existence of irrigation in summer, the type of crop and how crop rotations are carried out….