Africa’s projected population of 3.92 billion by 2100 presents significant challenges for food security. With climate change and soil degradation worsening, sustainable agricultural practices and soil health restoration are vital for long-term food security. The African Soil Health and Fertility Initiative (ASHFI), launched at the 2023 Africa Fertilizer and Soil Health Summit, aims to address these issues. While increasing mineral fertilizer use is key to revitalizing soil health, it is essential to consider its impact on soil organic carbon (SOC), a critical soil health indicator.
The Role of Mineral Fertilizers in Restoring SOC
SOC is crucial for soil structure, nutrient cycling, and resilience to drought. However, the use of mineral fertilizers in Africa is below the global average, limiting crop yields and biomass return to soil. While fertilizers can enhance biomass production and CO2 capture, they alone may not restore lost SOC. Long-term studies show that continuous fertilizer application may not improve SOC and could even reduce it, emphasizing the need for targeted management strategies.
Understanding How Mineral Fertilizers Affect SOC Dynamics
The balance between SOC accumulation and decomposition is vital for soil health. Mineral fertilizers can trigger a “priming effect,” increasing microbial decomposition of both plant residues and SOC. This can result in the rapid loss of plant residues as CO2, reducing SOC retention. Fertilizers may also shift microbial communities, favoring fast-growing microbes that decompose organic matter more quickly, further accelerating SOC loss.
SOC Loading and the Fate of Fresh Organic Matter
Soils with low initial organic carbon have a reduced capacity to retain additional carbon. Over-reliance on fertilizers may lead to a feedback loop that increases CO2 emissions while decreasing SOC. To break this cycle, it is essential to supplement mineral fertilizers with carbon-rich organic materials like compost and biochar, which help stabilize SOC and promote long-term soil health.
Future Steps: Applying High Rates of Organic Amendments
High rates of carbon-rich organic amendments, such as compost, should complement mineral fertilizer use. Studies show that a substantial one-time compost application can significantly improve soil properties and organic carbon levels. Combining compost with other amendments like biochar can further enhance soil health by promoting carbon sequestration and improving fertilizer efficiency.
Addressing Challenges and Limitations
Challenges in implementing these strategies include limited availability of organic materials, high costs, and competing resource demands. Solutions could include promoting local compost production, developing incentive programs for farmers, and exploring alternative organic amendment sources like agroforestry byproducts or municipal waste.
The Need for Long-Term Studies
Long-term studies across Africa’s diverse agroecological zones are crucial to understand how high carbon inputs and mineral fertilizers affect SOC and crop productivity. These studies can guide future agricultural practices to boost food security and climate resilience.
Conclusion
Revitalizing soil health in Africa is critical for sustainable development. While mineral fertilizers are essential for increasing yields, their effectiveness in restoring SOC is limited. Combining them with high rates of carbon-rich organic materials like compost and biochar will significantly improve soil health, boost crop productivity, and enhance nutrient use efficiency, ensuring long-term agricultural sustainability and climate resilience.
