Soil nutrient loss due to heavy rainfall threatens agriculture 

Phosphorus, a crucial nutrient for soil fertility and life sustainability, is increasingly vanishing from U.S. farmland, washing into rivers and streams at alarming rates. 

A new study led by researchers at the Pennsylvania State University reveals that despite efforts to curb phosphorus loss, agricultural runoff has continued to rise over the past four decades, posing significant threats to food security and water quality.

Soil nutrient and phosphorus loss

Phosphorus is indispensable for life, playing a key role in DNA formation and cellular energy transfer. 

However, unlike nitrogen, it is a non-renewable resource with limited geological reserves. Once it is lost from soil and enters waterways, it cannot naturally replenish in agricultural lands.

“This is a problem for many reasons,” said Li Li, professor of civil and environmental engineering at Penn State and corresponding author of the study. 

“When it’s lost from farmland, it can reduce crop yields, potentially leading to higher food prices. Then, when phosphorus enters our waterways, it can cause harmful algal blooms that can make water unsafe for swimming and fishing – and can even reduce oxygen levels in water and kill fish and other aquatic life.”

Li also highlighted the economic impact of phosphorus depletion: “It makes it more expensive to treat drinking water, which means higher water bills for all of us.”

Rising phosphorus levels in rivers

Analyzing data from 430 U.S. rivers spanning 1980 to 2019, the research team used a deep learning model to uncover troubling trends. 

While phosphorus levels have declined in 60% of the studied rivers, overall phosphorus flowing into waterways has increased.

“Agricultural areas are the biggest contributors to the problem, with phosphorus levels increasing in most rivers near agricultural areas, even as they decline in rivers near urban areas,” Li explained. 

“This suggests that efforts to control phosphorus pollution from sources like agricultural runoff are not as effective as we thought.”

By contrast, targeted efforts to reduce phosphorus pollution from urban wastewater treatment plants appear to be succeeding. 

Soil nutrient loss is beyond local control

However, the researchers warn that the broader problem is worsening due to factors beyond local control, particularly the increased frequency of extreme weather events linked to climate change.

“This means that even though we’re doing a better job at limiting phosphorus pollution from urban areas, the problem is getting worse overall, due to factors largely beyond the control of just one region,” Li said.

The role of climate change

Extreme weather events, such as heavier rainfall and flooding, have amplified phosphorus runoff into waterways. As storms grow wetter and more frequent due to climate change, the volume of water flowing through rivers increases, pulling more phosphorus from the soil.

“We’ve seen from recent weather events that water quantity, the amount of water that storms and waterways carry, can lead to dangerous flooding and mudslides,” Li said. 

“What we wanted to understand is what happens to the land when these storms pull the subsurface of the soil into rivers and streams. What we found is an alarming loss of this finite element that lets soil sustain life.”

Innovative solutions are needed

To combat this escalating issue, the researchers emphasize the need for innovation and changes in agricultural practices. One promising development is a technology invented at Penn State by alumnus Hunter Swisher.

Swisher, founder and CEO of Phospholutions, has developed a fertilizer designed to improve phosphorus efficiency in soil. “We are advocating for more innovation, more creativity and more urgency,” Li said.

The company’s product has shown remarkable results, reducing phosphorus runoff potential by 78% compared to conventional fertilizers. 

Phospholutions is now expanding its technology across the Americas, Europe, and India, aiming to address phosphorus pollution on a global scale.

Addressing soil nutrient loss

The study highlights the urgent need for comprehensive strategies to address phosphorus loss. 

With climate change exacerbating the problem, researchers call for a combination of advanced technologies and sustainable farming practices to mitigate the impacts on both agriculture and aquatic ecosystems.

“The connection between water and land is essential, and that balance is growing increasingly fragile,” Li concluded.

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