Kenyan farmers turn to sustainable methods to combat soil acidity

In an effort to combat increasingly acidic soil, farmers in Kenya are turning away from industrial farming methods.

Planting vegetables, Benson Wanjala and his wife are working to cultivate their two-acre plot of land on the outskirts of Nairobi.

This is a significant change to Wanjala's farming activities two and a half decades ago, when he farmed a 10-acre plot in his native western Kenya village, 370 kilometers away.

Back then, Wanjala's land yielded a bountiful harvest of 200 bags of maize each season.

But this abundance dwindled over the years to a mere 30 bags.

Decreasing crop yields

Wanjala attributes this decline to the acidifying fertilisers he used, which he believes rendered his once-fertile land lifeless and unable to support his family.

"I was advised to apply manure, but I wasn't keeping cows at the time," Wanjala recalls.

"Since I was wondering why the yield had reduced, I decided to move to Nairobi and start farming vegetables."

In Nairobi, Wanjala's vegetable farm initially showed promise.

But he soon noticed a reduction in yields here as well.

He suspects that the increased use of inorganic fertilisers is contributing to the decline in soil quality and productivity.

"My vegetable yield also began to decrease, and I suspect it is due to the increased amount of chemicals in the soil. I have no choice but to use fertilisers, as I need to make money to support my children," he says.

Despite the challenges, Wanjala remains committed to making a living through farming.

While he's aware of the adverse effects of inorganic fertilisers, the need to provide for his family necessitates their use.

His story reflects the broader struggles faced by many small-scale farmers who grapple with declining soil fertility and the pressures of urban farming.

Overuse of fertiliser

Priscilla Wakarera is a soil scientist and chief executive of Rhea, a soil health management company.

Rhea helps farmers maintain soil health by offering soil testing services through its "Rhea Agripad" device.

The device plugs into a composite soil sample, runs an analysis, and provides results in a few minutes.

Wakarera says many farmers double their fertiliser application if they experience low yields during a season.

But if the soil's pH is unfavorable, the existing minerals in the soil cannot be absorbed by the plants, and adding more fertilisers exacerbates the problem.

"We have very high soil degradation as a result of accumulation of fertiliser metals in the soil due to overuse of specific fertiliser," she says.

"And what this does is it that it changes the soil pH to acidic and when the soil pH is acidic the plant is not able to absorb the available nutrients in the soil."

In Kenya, many farmers favor DAP (Diammonium phosphate) fertiliser for maize, but its continuous use can lead to high soil acidity.

Soil testing

Wakarera says soil testing is important to determine acidity levels before deciding on a particular fertiliser application.

She says improper use of chemical fertilisers, along with poor farming practices like monocropping and the prevalence of counterfeit fertilisers, contribute to soil degradation in sub-Saharan Africa.

High soil acidity diminishes biodiversity and reduces beneficial microbes essential for processes such as nitrogen fixation in legumes.

To combat this, Wakarera is calling for regenerative agriculture, recommending bio-fertilisers, green manure, or biochar as more sustainable alternatives to chemical fertilisers.

"The lack of soil data has led to the wrong use of chemical fertilisers in a bid to increase yield, and it is having an opposite effect from what is required," she says.

Wakarera notes that farmers using chemical fertilisers are often two generations into the practice without historical data to guide proper usage.

Despite the challenges, Wakarera says, when used correctly, chemical fertilisers can boost crop yields.

Farmers say access to conventional soil testing is limited and takes too long, up to a month, to get results.

They also say liming – which reduces acidity – is costly.

For farmers like John Mburu Gitu, enlisting the help of a soil scientist is proving beneficial.

Gitu saw his avocado farm's yield increase after soil testing.

"For my first harvest, I managed to get 1,100 kilograms. After conducting soil testing on my farm, my yield increased to 1,800 kilograms," he says.

Long-term fruits

Elizabeth Atieno Opolo, a crop scientist and food campaigner at Greenpeace Africa, says overusing synthetic fertilisers can be damaging.

Excessive nitrogen, for example, can lead to nitrogen leaching, causing water pollution in aquifers and rivers.

Opolo also supports sustainable agricultural practices, such as intercropping and crop rotation, over monocropping.

"Sustainable agriculture takes time, but you can be able to see the long-term fruits of it," she says.

"Industrial agriculture is a quick fix, but it leaves you with dead soil, it leaves you with a dead environment."

Greenpeace Africa collaborates with small-scale farmers to raise awareness about transitioning from industrial to sustainable farming methods.

They're urging governments to enact laws supportive of sustainable agricultural practices and to provide officers to assist in the transition.

A continental problem

According to the Alliance for a Green Revolution in Africa (AGRA), about 63% of Kenya's arable land is acidic, resulting in a decline in the production of staple crops like maize, as well as key exports, such as horticulture and tea.

The Food and Agriculture Organization (FAO) reports that Kenya's maize production dropped by 4% to 44 million tonnes in 2022, meaning increased imports to cover the shortfall.

This issue of declining agricultural productivity is not confined to Kenya.

Across Africa, the continent holds 65% of the world's remaining uncultivated arable land.

But it spends approximately $60 billion annually on food imports to meet its needs, according to the African Development Bank