How the zaï technique is helping farmers adapt to climate change in the Sahel

“On a cosmic scale, liquid water is rarer than gold,” wrote the famous astrophysicist Hubert Reeves. What is true for the universe is even more true in the Sahel, this immense arid strip that runs through Africa from east to west, on the edge of the Sahara. In the Sahel, the first of goods is water. Since the third millennium BC, the peoples of the region have made considerable efforts and deployed treasures of imagination to capture and control this rare resource. Faced with water that is poorly distributed in space and time, they had to invent intelligent and parsimonious methods to take advantage of the smallest drop.

Once ignored, the secrets of Sahelian farmers are now attracting the attention of researchers and decision-makers. And for good reason, they inspire new ways of adapting to climate change for African agriculture, and beyond.

Every year in Yatenga, in the north of Burkina Faso, the first rains of June come to soothe the burns of an interminable dry season. The water-soaked soil then brings life back to the bush fields. Almost everywhere, clumps of millet and sorghum spring up from the ground, transforming the arid savannahs into verdant groves.

But in some villages, the period of great drought in the 1970s and 80s upset the fragile Sahelian ecosystem: with the thinning of the vegetation cover, the unstable and ferruginous soils of the Yatenga were stripped by erosion; they have become so poor and encrusted that the torrential rains only run off without being able to infiltrate. Instead of bringing life, water erodes the land and carries away the hopes of the peasants.

In this hostile landscape, some farmers are trying to adapt and innovate. Yacouba Sawadogo is one of them. In a barren field in the village of Gourga, Yacouba and his family are busy breaking through the crusted soil before the first rains arrive. Armed with their daba (traditional pickaxe), they dig the red laterite earth. In a vigorous choreography, the peasants crisscross the plot with these regular holes. They slip in a handful of compost, a few sorghum seeds, a film of light soil: and voila, the field is ready to welcome the next rainstorm!

Sowing seeds like this in the middle of the dry season, in a field that is strewn with holes, the idea may seem counter-intuitive to the outside eye, but it is in fact part of the centuries-old expertise of the inhabitants of Yatenga: the zai. This revolutionary agricultural technique has made them masters of the art of capturing rain. Oral history tells that in ancient times, the technique was used by families with very small areas and poor land, before falling into oblivion in the 1950s, a period marked by abundant rains.

But in the desperately dry decades of 1970-1980, faced with the advance of the desert, Yacouba Sawadogo made a singular choice: that of not fleeing. Instead, he unearthed zaï, a technique through which he managed to revitalize and reforest 27 hectares of degraded land. The man who is nicknamed “the man who stopped the desert” thus gave hope to his whole village. Awarded "Champion of the Earth" by the United Nations and made famous thanks to a book, Yacouba Sawadogo has become the symbol of an Africa that innovates in the face of desertification.

Just a hole, you tell me? Behind an apparent simplicity, the zaï is actually based on complex ecological mechanisms. The technique consists of concentrating water and manure to promote crop growth in a context where rain is as rare as it is random. To do this, we prepare during the dry season pockets, that is to say holes 10 to 15 cm deep and 20 to 40 cm in diameter to deposit organic fertilizers and sow cereals (millet or sorghum).

When the rains come, the amended poquet fills with water and releases nutrients that attract termites of the genus Trinervitermes. These insects dig galleries through which the water infiltrates deeply, and via their droppings, they transform the organic matter which then becomes assimilable by the plants. This process results in the formation of a moist, fertile pocket where the plant develops its roots. Some authors claim that with zaï, millet and sorghum yields can reach 1500 kg of grain per hectare against less than 500 kg per hectare under normal conditions.

In addition to being economical and bringing good yields, zaï also promotes the return of trees to the fields. The pockets tend to trap the seeds of many tree species, the latter being transported by the wind, runoff water and the droppings of farm animals. When the rains arrive, shrubs develop spontaneously alongside the cereals, in the rich and humid environment of the zaï holes.

In the Yatenga region, some farmers preserve and protect these young trees, a source of natural fertility and fodder in the dry season. In Senegal, researchers from the Senegalese Institute for Agricultural Research (ISRA) and the National Institute of Pedology (INP) are currently carrying out trials to assess the amount of carbon sequestered in the soil thanks to zaï. Their first results show that in the treated plots, the carbon stock per hectare increases by 52% compared to the control plots. A promise of generous harvests and a provider of ecosystem services, the zaï definitely has everything to seduce.

The only problem is that this technique requires a significant amount of manual labor and substantial investment. At the rate of 4 hours a day, a single man with his daba will have to dig for 3 months to develop one hectare. What's more, it will be necessary to manufacture or buy 3 tons of manure to improve the pockets. It is not for nothing that in the Mooré language, zaï comes from the word “zaïégré” which means “to get up early and hurry to prepare your land”.

Mali, Senegal, Niger, Kenya… once rediscovered in Burkina Faso, zaï was quick to spread beyond its original cradle. In the 1980s, development aid deploys significant resources to combat desertification in the Sahelian territories weakened by the great drought. Present in the Yatenga region since 1982, a team of agronomists from CIRAD already described the zaï technique there as a promising way of restoring land.

Then began a wide range of projects and programs that sought to test, disseminate and improve zaï in sub-Saharan Africa. In Burkina Faso, the Institute for the Environment and Agricultural Research (INERA) and NGOs such as Solibam have mechanized the production of the pits to lighten the workload. Instead of digging manually, we make cross passages with a tine hitched to an animal and we sow at the intersection of the furrows. With this technique, the working time goes from 380 to 50 hours per hectare. In the rural commune of Ndiob, in Senegal, Mayor Oumar Ba went even further by distributing mechanical augers to farmers, making the production of pits very easy and quick.

In Burkina Faso, as part of the Fair Sahel project, INERA researchers are carrying out agronomic trials aimed at replacing part of the organic manure from zaï pockets with microdoses of mineral fertilizer. A way to improve sorghum yields while removing a major obstacle to adoption: the high cost of organic matter. Agronomists are also working to combine cereals such as sorghum with legumes such as cowpea in the same pockets. Finally, they are testing zaï on new crops, such as corn, cotton, watermelon and horticultural crops such as eggplant.

In the market gardening areas of Senegal, the zaï technique has also spread, producing numerous avatars. When water becomes scarce and expensive, farmers seek by all means to save the resource. In Fatick in the west, they use recycled tires to concentrate the inputs of manure and water at the level of the roots of the pepper plants. In the coastal region of Mboro, they carve the onion plots into tiny bins which they flood with a seal. To the south, in Kolda, they transplant the aubergines into pockets covered with straw. These innovations are frugal and all follow the same logic: to concentrate water and fertility in small pockets of life, sheltered from a hostile external environment.

In response to climate change, states around the world have entered into a competition to increase the availability of water for their agriculture. Dams, mega-basins, irrigated perimeters… everywhere, the dominant policy is to extend irrigated areas at all costs.

But this choice, if it responds to a short-term need, is accompanied by a serious risk of “mal-adaptation” : degradation of water resources, social injustices and geopolitical tensions are the hidden counterpart of major hydro-agricultural projects. The agricultural model that is taking shape for tomorrow seems very fragile and vulnerable, because it depends on water captured and routed with a lot of fossil fuels.

Going against the current of the dominant innovation regime, Sahelian farmers have chosen the path of sobriety. Confronted for centuries with significant limitations on water resources, these millions of "barefoot researchers" have continued to innovate in silence. Instead of "always more water, whatever the cost", they preferred a principle of parsimony. And the zaï, as publicized as it is, is only the tip of the iceberg: half-moons, stone cordons, fruit bowls, ponds, stratified cultures... These ancestral techniques deserve our full attention because they represent intelligent forms adaptation to extreme thermal and water conditions, close to what the Mediterranean countries will experience in 2100 in a climate scenario at +4°C.

To build a new narrative on the global future of water, let's listen and listen to the secrets of Sahelian farmers.