Kareem Explores How Biochar and Nitrogen Fertilizer Can Boost Maize Yield, Improve Soil Health

February 5, 2024

Emma Okonji

A Nigerian soil scientist, Mariam Olamide Kareem, has shed new light on the potential of biochar and nitrogen fertilizer to improve maize performance and support long-term soil sustainability, following a detailed study on selected soil physical properties.

Kareem, whose research examined the interaction between biochar application and nitrogen fertilization under continuous cultivation, said the findings could help farmers balance productivity needs with the preservation of soil health—an increasingly urgent challenge as population growth drives intensified land use.

Kareem explained that traditional soil-restoring practices, such as fallowing, have nearly disappeared under socioeconomic pressure, leaving soils depleted and farmers more dependent on inorganic fertilizers.
“Continuous farming without replenishing organic matter has weakened our soils,” she said. “Farmers rely heavily on inorganic fertilizers, but high costs, inconsistent supply, and long-term degradation risks make this approach unsustainable.”

Her study highlights biochar—a carbon-rich material produced from heating organic matter in the absence of oxygen—as a promising soil amendment. The material has been globally recognised for improving soil structure, boosting nutrient uptake, mitigating pollutants, and enhancing crop stress tolerance.

However, Kareem noted that while biochar is widely praised, its interaction with nitrogen fertilizer has shown mixed results across different studies.

“Biochar is not a magic solution,” she said. “Some international studies even reported reductions in nitrogen retention. That is why we needed local evidence under our own soil and climatic conditions.”
In her findings, Kareem observed that applying biochar alone or in combination with nitrogen fertilizer did not significantly alter key soil physical properties such as bulk density, field capacity, saturation capacity, or available water capacity.

But the combination still delivered a major benefit: maize performance improved significantly with nitrogen fertilizer application, even at reduced levels.

“One of the most important outcomes is that maize responded strongly to nitrogen fertilizer, even at lower application rates,” Kareem stated. “This means farmers can achieve better yields without applying excessive fertilizer—saving costs and protecting the soil.”

Her data showed increases in plant height, stover production, and grain yield, with the highest performance observed at full nitrogen application levels. According to her, this suggests that nitrogen remains critical for maize productivity, but efficient use—especially alongside soil amendments—can reduce the overall burden on farmlands.

Kareem emphasized that while initial results are promising, long-term trials are essential for fully understanding how biochar may influence soil physical properties over time.

“Soil health is not restored in one season,” she explained. “We need multi-year studies to determine how biochar behaves in our soils and how it can support sustainable food production for the future.”
She called for increased investment in soil research, farmer education, and low-cost soil-building technologies to secure Nigeria’s agricultural resilience.

“If we are serious about food security,” Kareem said, “we must prioritize practices that rebuild soil, improve efficiency, and support farmers who carry the burden of feeding our growing population.”
Her study contributes to emerging evidence that strategic combinations of biochar and nitrogen fertilizer could help enhance global maize productivity while slowing soil degradation—an approach experts say is vital for sustaining agriculture in the decades ahead.