Regional researchers join hands to tame soil acidity

Faustine Munyakayanza , a farmer from Nyamagabe, Southern Rwanda, at his wheat farm. The wheat was grown on extremely acidic soils. 


What you need to know:

  • A group of scientists from Kenya, Rwanda, Tanzania and Ethiopia are working on a project to address knowledge gaps related to acidic soil as well as improve crop productivity in these four Eastern African countries.

Are you noticing a decrease in your farm's crop yields despite following proper agronomic practices, such as using appropriate seeds and fertilisers at the right time? The cause may be soil acidification. By addressing this issue, you could increase your yields twice or even thrice in two to three seasons.

A group of scientists from Kenya, Rwanda, Tanzania and Ethiopia are working on a project to address knowledge gaps related to acidic soil as well as improve crop productivity in these four Eastern African countries.

“Most acidic soils, especially those plagued by aluminium toxicity, can only be corrected using lime. However, we are analysing it holistically to come up with instruments that will inform agricultural lime manufacturers, transportation of lime to the farmers, policy environment in each of the countries and alternative ways of managing acidic soils without necessarily using lime,” said Dr Frédéric Baudron, the lead researcher for the project known as Guiding Acid Soil Management Investments in Africa (GAIA).

Soil acidification in Ethiopia is mainly caused by heavy rainfall, which removes basic cations through leaching. Other factors include parent material, ammonium-based fertilisers and the removal of biomass. (Published in Journal of Agricultural Science and Botany, 2021)

A new handbook by the Kenya Agricultural and Livestock Research Organisation and Gatsby Africa reveals that 63 per cent of Kenya's arable land has acidic soil, affecting food production. Few farmers have implemented acid soil management techniques. The handbook was launched in August 2023 by the Agriculture CS.

And now scientists under the leadership of the International Maize and Wheat Improvement Centre with support from Bill and Melinda Gates Foundation (BMGF) are convinced that guidelines for acid soil management in the four countries, conducive political environment, inclusion of the private sector and building capacities of smallholder farmers to start managing their acidic soils will double food production in the region.

“Soil health has always been looked upon as a subject for soil scientists, ignoring the economics, the policy aspect and the business sector aspect,” said Dr Baudron, noting that the GAIA project is tackling the subject from all those angles.

However, even without standardised guidelines for acid soil management, farmers from a country like Rwanda, which has quickly embraced acid soil management, with the government coming in to offer 50 per cent subsidy on the cost of lime, have recorded very impressive yields.

Mukogatare Verida from Nyagahinga Village of Nyaruguru District in Southern Rwanda says she was able to double her yield of beans last season when she applied lime on her two-acre piece of land.

Faustine Munyakayanza, a wheat farmer from Mujuga Village of Nyamagabe District in the same region, also recorded a more than double yield from his three-acre piece of land.

According to Dr Vicky Ruganzu of the Rwanda Agriculture and Animal Resources Development Board (RAB) and the country project lead for GAIA, liming has shown a positive and significant effect on crop yields in the country. “For farmers who have embraced the application of lime for acid soils, we have witnessed a yield response ranging between 15 - 30 per cent for Irish potato, 36 - 44 per cent for maize and 44 – 58 per cent for beans.”

However, Dr Ruganzu is quick to caution that lime can only be used alongside fertilisers or manure, with good agronomic practices such as terracing on sloppy landscapes and using other relevant inputs such as appropriate seeds.

Despite the promising yields, the country is still grappling with the high cost of transportation of lime from places like Musanze, which is located in the North, to places like Nyamagabe in the South. According to Dr Ruganzu, the transport takes the main share of farmers' final price for farm input.

So far, the GAIA scientists have established that soil testing for pH as an indicator of soil acidity is insufficient to warrant the need for the application of lime.

“On one hand, we have a good understanding of the sensitivity of different crops to aluminium toxicity or low soil pH, where there is a high probability of response to lime, and lime is probably the only intervention that can really address the problem,” said Christian Witt, a senior programme officer at BMGF.

On the other hand, he said, “We have soils that can easily respond to other interventions other than application of lime.”

“But what I really appreciate in the GAIA project is the very systematic analytical approach and also to look into, not just issues from an agronomic perspective, but also from an economic perspective, from smallholder point of view as well as distribution of lime across the countries,” said Witt.