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In parts of Tanzania, soils are disappearing. A combination of climate change and socioeconomic stresses has led to soil crumbling away into nearby rivers and lakes.

Recognising the threat, one community set up an environmental committee to allow strategic decision-making for soil restoration. They worked with researchers led by Will Blake at the University of Plymouth in collaboration with the Nelson Mandela African Institution for Science and Technology, who are experimenting with a portable gamma ray sensor that can quickly assess the health of the soil. The community identified areas where the soil was severely depleted, and so excluded their cattle. With the pressure removed, the land re-greened quickly and the soil began to recover.

Soil health is crucial to agriculture. Unsustainable practices like heavy fertiliser use and ploughing lead to fragile soil that washes away in heavy rains – reducing the land’s productivity in the long run. Further threats come from climate change, which is causing more frequent extreme weather events like droughts and heavy rains – leading to even more soil erosion. “Landscapes are starting to unravel,” says Blake, “and there are consequences at large scale.”

The solution is to understand the soil better, in particular, what makes it healthy and resilient, to develop more sustainable and climate-smart farming.

New sensor technologies promise to revolutionise soil health monitoring. Traditionally, this is done by taking a small number of samples for lab analysis, which only gave a smattering of data points. The newer approaches, such as gamma sensing, allow rapid surveying of fields and farms.

Blake emphasises that the technology is only half the story. “Collecting quantitative evidence through a natural science lens isn’t enough,” he says. Soil data has to enable farmers to devise and enact solutions and the sensor technology helps.

Scientists helicoptering in and proffering solutions doesn’t work, partly because it ignores the autonomy of the farmers themselves, and partly because it neglects their extensive local environmental knowledge. Instead, Blake favours “mutual learning” in which the different groups learn from each other and talk openly.

This collaborative approach is already paying dividends. In a previous project using a different sensor, some farmers made dramatic changes. “During past seasons I used to get 4–5 bags of maize per acre using improved varieties of seeds and intensive use of fertilisers,” one reported. After scanning his soils, he switched to farmyard manure and intercropping between maize and beans, in a bid to increase soil nitrogen and agriculture productivity. “Now I am getting 7–9 bags of maize in the same piece of land”.

In Tanzania, researchers first assumed that soil erosion was caused by overgrazing. But when they spoke to local people, they realised the grazing decisions were actually a symptom of deeper problems, such as agropastoralists being pushed onto less suitable lands by population growth and other factors. Climate change is also changing rain patterns in east Africa. “The short rains sometimes just don’t come,” says Blake, while the long rains often come late or are “devastatingly hard”. The communities are aware of all these factors.

While this pilot work has focused on the Global South, Blake says there’s a lot the Global North can learn from these experiences. Many countries are moving towards regenerative agriculture, which aims to restore soils and ecosystems to make farms more resilient and sustainable. This will involve embracing many practices that are common in the Global South, but which the Global North abandoned when it adopted industrial farming. Blake says there are many “lost wisdoms” that older generations of farmers knew. “We’ve realized that developing the evidence base together with the communities affected is the most effective way,” he says.

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