African Farmers Could Optimize Crop Production with Phosphorous Fertilizers, but Cost will be Great

By the middle of the century, crop yields in Africa could be nearly 30 percent less than what's optimal because of the underuse of phosphorous-based fertilizer, according to a new study published in the journal Global Change Biology.

Africa's yield gap - the difference between how much crops could produce in ideal circumstances compared to actual yields - is currently around 10 percent for subsistence farmers, but that gap is poised to grow to 27 percent by 2050, according to researchers from the International Institute for Applied Systems Analysis (IIASA).

"This research shows that the imbalance between nitrogen and phosphorus applications has the potential to further limit food production for a growing population in Africa," said Marijn van der Velde, a researcher who led the study while working at IIASA.

Van der Velde said that farmers' limited financial resources play a large role in the current yield gap. Phosphorous-based fertilizers are more expensive than nitrogen-based ones.

"Farmers with limited money are more likely to buy and have access to cheaper nitrogen-based fertilizers," said van der Velde. "While this might work in the short term, in the longer term it has a negative effect on crop growth as soil nutrients become more imbalanced."

In addition to helping a current crop cycle grow, fertilizers impart nutrients in soils over time, providing a reserve of useful nutrients plants can use to grow.

Overall fertilizer use in Africa remains low, but it is wildly recognized that African farmers must increase their use of fertilizer to increase crop production, the IIASA said in a statement.

"And while nitrogen-based fertilizer usage has begun to increase in Africa in the last 10 years, the application of phosphorus to cropland has not kept pace, leading to a growing imbalance between nitrogen and phosphorus levels in soil," the IIASA wrote. "The new study shows that increases in nitrogen and phosphorus inputs must happen in a way that provides crops with the balanced nutrient input they need."

IIASA researcher Christian Folberth said that while previous African crop studies have looked at the effects of fertilizer use on a local scale, this work is the first to address the issue for the entire continent.

The researchers used data from the United Nations Food and Agriculture Organization (FAO) and a large-scale crop model to estimate how the soil nutrient imbalance affects current and future crop yields.

The study revealed the levels of phosphorous needed in African soils to make optimal use of current nitrogen levels in the soil, as well as what would be needed to close the current yield gap.

However, because of the cost of phosphorous, doing so will be a challenge.

"While much of the remaining phosphorus reserves are found in Morocco, on the African continent, we need to find better ways for African farmers to access this precious resource," van der Velde said, adding that the imbalance of soil nutrients is not isolated to Africa.

"The change in the stoichiometry of nitrogen and carbon from rising atmospheric CO2 concentrations relative to phosphorus has no equivalent in the Earth's history and the impacts will go beyond the agricultural sector," van der Velde said.