Managing soil for improved yields


At 200 million years old, and in the absence of volcanic and glacial rejuvenation, most African soils have lost their natural fertility. PHOTO | SHUTTERSTOCK

For many years, inappropriate land use, poor management and lack of inputs have led to soil erosion, salinisation causing decline in productivity and further affecting food security in Africa. Scenes of drought and people dying of famine in the region are not only linked to weather patterns but also to soil fertility management.

A paper by Obed Lungu and Mustapha Naimi entitled African Soils: Their Productivity and Profitability of Fertilizer Use presented during the African Fertilizer Summit 9-13th June 2006, Abuja, Nigeria said that despite the important role that fertility in soil management plays, not much has changed.

"Regenerative” agriculture involves a number of principles to replenish the soil, reduce erosion and improve nutrition. At 200 million years old, and in the absence of volcanic and glacial rejuvenation, most African soils have lost their natural fertility. Other studies have also shown that healthy agricultural soils play a significant role in climate change mitigation and adaptation by storing (or sequestering) carbon, soaking up water like a sponge, and reducing nitrogen loss to the environment.

In nature, silicates of rocks like basalt react chemically with carbon dioxide (CO2) in acidic rain and are eroded as a result. This leads to an enhanced weathering process which accelerates the natural process by deliberately covering farmland with crushed silicate rocks, further hastening chemical reactions between rocks, water, and air. In so doing, we remove CO2 from the atmosphere and bind it in carbonates for thousands of years.

Importantly, these rocks also contain nutrients, so we decrease the need for potassium and micronutrient fertiliser, and agricultural lime. Such outcomes, and the stronger resilience to drought, are hugely beneficial for Kenya’s food security and nutrition, and farmers’ incomes.

Dr Lydia Olaka, a senior lecturer at the Technical University of Kenya, and George Okoko have been studying basalt rocks in the Kenya rift and Marsabit in the north. Their research, Can East African rift basalts sequester CO2? Case study of the Kenya rift, published in 2021, established that the basalts from the region can store a lot of CO2 through capturing and underground injection. The high permeability of rocks, availability of water, close proximity to CO2 production sites, and appropriate basalt volumes could mitigate against climate change and remineralise the soil.

The research by Olaka and Okoko also reveals that rains in and around the 6,300 km² Mount Marsabit basaltic shield volcano are rare. The higher elevations are covered by forests which are sustained by fog, but the low-lying semiarid savanna region turns into a bustling greenfield during the rainy season.

The Lotikipi aquifer, discovered in 2013 beneath Turkana's desert, is also believed to contain 200 billion cubic metres of water further making the region to be productive. But although the underground water is saline, God gave the region lots of wind that is now propelling some 300 megawatts of Kenya’s green energy. Our role in accelerating productivity is to connect the dots by leveraging the energy to desalinate the water, irrigate the dry land and ensure food security for the people. The area that we have always considered as arid and semi-arid is perhaps the future food basket for Kenya.

Currently, Olaka has teamed up with scientists at the University of Antwerp in Belgium and the International Institute of Tropical Agriculture in Kenya to further her work. Last week, I was fortunate to meet with the scientists, including Professors Sara Vicca and Ivan Janssens, Dr Eric Struyf and Dr Dries Roobroeck, who are doing research on enhanced weathering to improve food security and mitigate climate change.

On the other hand, a research paper: Negative erosion, and negative emissions: Combining multiple land-based carbon dioxide removal techniques to rebuild fertile topsoils and enhance food production, published in 2022 by Janssens and others argue that carbon dioxide removal (CDR) that expands the area of forest cover or bioenergy crops inevitably competes with crop and animal systems for land, jeopardising food security, or encroaches on natural lands, jeopardising biodiversity.

Balancing these conflicting demands, the research presents a daunting challenge, particularly in the global South, where agriculture is essential to sustaining people's livelihoods and where arable land is severely degraded and yields are low, or where the land is currently not suitable for farming.

CDR strategies like enhanced silicate weathering, biochar amendment, and soil carbon sequestration avoid this competition for land and should even have numerous co-benefits for food production.

Declining productivity as a result of land use and failure to regenerate is forcing farmers to seek more land which is not available. Even if it were available, the expansion increases the threat of climate change. 

The writer is Kenya's Ambassador to Belgium, Mission to the European Union, Organisation of African Caribbean and Pacific States and World Customs Organisation.