Africa needs balanced soil nutrients and water, not another fertilizer target

Alex Awiti

November 30, 2023

I visited a feisty grandmother in Kisumu County, Kenya, a few years ago. Abol was 75 years old then. As she approached to greet us, her gait was sure, and her smile was heartful. Her calloused hand clasped mine gently.

We exchanged pleasantries. We talked about the good old days, rains that never tarried, fertile land and bumper harvests, the trees and lush shrubs clothed the slopes yonder, and the crystal-clear waters rolled gently and steadily from the springs.

Like a platoon leader, she gestured and marched ahead. We stopped at a little mound on the edge of the farm for a sweeping, picturesque view of her field and the village beyond. Like her neighbors, Abol’s half-acre field had maize. In the middle of the growing season, the maize was thin with spindly stalks, barely one meter tall. One would think that Abol and her neighbors planted a purple-leaf variety of maize. Interspersed with the maize was striga, a root parasite that affects maize, millet, sorghum, and legumes, causing severe wilting and stunting. The prevalence of Striga is symptomatic of acidic soils, low organic matter, and low phosphorus.

A sweltering house without food

In Abol’s farm, the bare soil, deprived of any cover or plant litter, stretched like an old, tired brown rug beneath the dominant maize-striga weed mosaic. The baking heat and the absence of organic matter are not creature–comfort–packed dwellings for soil micro-organisms. It’s hard to live and thrive in a sweltering house without food.

Starved of carbon, moisture, and nutrients and with a root parasitic weed, striga, sucking nutrients from it, Abol’s maize has no chance. The yield from the last season was a measly 500kg per hectare. Like many smallholders in western Kenya and sub-Saharan Africa, Abol cannot feed her grandchildren. Households like Abol’s are short of food 110 days a year.

Higher fertilizer application rates do not solve Africa’s low productivity trap.

Rural households in sub-Saharan Africa are in a low productivity and poverty trap. The trap is maintained by soil nutrient mining and the inherent constraints of low soil organic carbon and high soil acidity, which causes variable yield responses to applied inorganic fertilizer.

Research conducted in Kenya’s western and central highlands shows that maize yields remain at two tons or lower even when 150 kg/ha of nitrogen is applied to low-potential soils (when organic carbon is less than 3 percent and the soil is acidic with a pH below 5.5). Conversely, in soils where organic carbon is higher than 3 percent, and soil pH is above 6, maize yield of up to 3.5 tons/ha can be achieved with less than 20 kg/ha of nitrogen fertilizer.

Variations in fertilizer use and maize yield in sub-Saharan Africa are instructive. According to FAO, Uganda’s fertilizer application rate is 2.4 kg/ha, just 4 percent of Kenya’s 60 kg/ha. But Uganda produces 2.84 tons of maize per hectare, 87 percent more than Kenya’s 1.52 tons/ha. With about two-thirds of Kenya’s fertilizer application, Ethiopia produces 179 percent more maize than Kenya.

‘Biochar can alleviate agronomic constraints of tropical soils’

Higher fertilizer application rates or blends cannot address Africa’s low productivity trap. Meeting the 50 kg/ha Abuja Declaration fertilizer target or whatever new target must not be the singular focus of the 2024 Africa Fertilizer and Soil Health Summit. The focus must be on the integrated and complimentary use of inorganic fertilizers and organic resources to restore optimal soil nutrient balances and break the low productivity trap.

Africa needs massive public, private, and philanthropic investments to recapitalize soil productivity in sub-Saharan Africa. To achieve this objective, we need technical innovations in complementary use and efficient delivery of inorganic and organic nutrient sources, combined with agroecological redesign of farming systems to rebuild soil organic matter. Rebuilding soil organic matter can be achieved by intercropping, improved rotations, and fallows, including agroforestry, legumes, grasses, and livestock integration.

Advances in innovation in producing and using organic resources for soil amendment and the efficient delivery of inorganic and organic nutrient sources are encouraging. For example, when used as a soil conditioner and nutrient carrier, biochar can alleviate agronomic constraints of tropical soils by increasing soil organic carbon, reducing soil acidity, improving moisture and nutrient retention, providing habitat for beneficial soil micro-organisms, enhancing the availability of nutrients like phosphorous and raising crop productivity. Biochar is a stable, carbon-rich, highly porous material produced by burning organic matter under limited oxygen conditions.

‘Biochar optimizes the composting process’

Biochar is a cost-effective, slow-release carrier of N (nitrogen) fertilizer. Biochar‑based controlled-release N fertilizers (BCRNFs) increase N use efficiency by improving the synchrony between N supply and crop demand, modulating the abundance of beneficial soil microbial communities, reducing losses from leaching and volatilization, and increasing grain yield.

Promising technologies for producing BCRNFs comprise physicochemical methods such as physical mixing, coating, and graft co-polymerization. Studies reveal an improvement in fertilizer use efficiency in BCRNFs and a delay in the cumulative release of N of up to 65 percent and 69 percent, respectively, compared to traditional chemical fertilizers.

Biochar optimizes the composting process, including an increase in microbial and enzymatic activity, improved composting efficiency and quality, and causes an increase in the alkalinity of the compost.

Moreover, according to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC), there is robust evidence that “biochar has significant mitigation potential through carbon dioxide removal (CDR) and emissions reduction and can also improve soil properties, enhancing productivity and resilience to climate change.”

According to IPCC, soil carbon management in agriculture using biochar can remove about 1.8 to 4.1 gigatons/year of CO2. CDR credits can be sold in voluntary carbon markets, providing an additional revenue stream for biochar producers.

A paradigm shift for Africa’s agriculture

The Africa Fertilizer and Soil Health Summit must deliver a paradigm shift. Fertilizer manufacturers, the private sector, farmers, universities, and research institutions can spearhead path-breaking innovations and investments in the recapitalization of Africa’s soils that simultaneously rebuild soil organic matter, enhance fertilizer use efficiency, reduce fertilizer use and tap into the emerging CDR credit markets.

By advancing biochar and agroecological innovations, we can transform agriculture from reliance on external chemical inputs to a regenerative model based on adaptive and resilient biological and ecological processes.

The global biochar market is growing at a compound annual growth rate of 13.53 percent compared to 3.3 percent for the global fertilizer market and is projected to reach 5.2 billion dollars by 2030. Africa must mobilize resources to produce and develop a biochar market for agriculture and tap into the emerging CDR credit markets. The use of crop residues (sugarcane, rice, wheat, maize, coffee, cocoa, coconut, palm, groundnuts, etc.), wood waste, and short-rotation coppicing trees as biochar feedstock could create a vibrant circular economy in agriculture, with new revenue for farmers and millions of jobs for the youth.

The Africa Fertilizer Summit should not produce a new fertilizer application target. The Summit must catalyze and mobilize investments for innovations in the efficient use and delivery of organic and inorganic and organic resources and small-scale distributed irrigation systems. We owe it to Abol and her grandchildren.


Alex O. Awiti is a Principal Scientist at World Agroforestry (ICRAF).