Trash to Treasure? Increased Soil Phosphorus in Farmed Urban Soils
A survey of farmed soil from Kumasi, Ghana into the surrounding countryside reveals that long-term history of farming and proximity to the city leads to higher soil phosphorous availability.
A recent study in the Journal of Geophysical Research: Biogeosciences highlights how urbanization can lead to an increase in soil phosphorus levels, a critical nutrient for plant growth. Researchers Asabere and Sauer examined soil samples from farms near Kumasi, Ghana, which are surrounded by rapidly expanding cities. Tropical soils in this region are typically low in phosphorus, but the study found that farms with a long history of food production contained higher phosphorus concentrations.
The researchers discovered that as urban areas infiltrate these farmlands, waste materials such as broken cement, charcoal, ash, and wash-water gradually accumulate in the soil. These urban waste products contribute to a shift in phosphorus availability, transforming it from a form that is hard for plants to absorb (mineral-occluded) to a form that is readily taken up by plants (calcium-bound).
This transformation indicates that urban waste plays a significant role in enhancing the phosphorus content and diversifying its storage in these soils.
The findings underscore the importance of small-scale farming in local economies, particularly in regions where cities are expanding. The study emphasizes the need for further research into the soils that are often overlooked in environmental studies but are vital to regional food security and livelihoods. The paper, authored by Asabere and Sauer, is available in the Journal of Geophysical Research: Biogeosciences with the DOI 10.1029/2026JG009815.
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