In many parts of the world, including China, soil acidification is reducing agricultural yields. Recycling animal manure can help counteract this acidification and is therefore a key component of circular agriculture. However, this approach also has a downside.
New research by Wageningen University & Research (WUR), published in Nature Food, shows that large-scale manure use can lead to the accumulation of cadmium (Cd) in soils, and ultimately in rice, exceeding food quality criteria. It highlights the need to consider the entire system: from soils and fertilisation practices to industrial emissions and the food chain.
"What benefits the soil in the short term may pose risks to food safety in the long run," says Dr Donghao Xu. "This trade-off cannot be resolved by looking at agricultural practices alone."
Using coupled models of soil processes and metal transport, the researchers simulated the long-term effects of different nutrient management and liming strategies over several decades to reduce soil acidification and thereby Cd uptake by crops. The results show that relying solely on either manure or even lime to enhance soil pH is insufficient to avoid long-term adverse Cd impacts. Instead, a combination of management: maintaining soil pH levels while simultaneously reducing cadmium deposition by stricter control of industrial emissions, is required to avoid Cd levels in rice that exceed the quality criteria.
"This research shows that circularity cannot be considered in isolation from its wider environmental context," adds Prof Wim de Vries. "If we want to close nutrient cycles, we also need to ensure the quality of the material that is used to close those cycles."
The findings are relevant far beyond rice production systems in Asia. Across the globe, similar challenges are emerging around manure management, soil quality and contamination risks. Policy decisions in agriculture, industry and environmental protection are closely interconnected. This study underlines that effective pathways towards sustainable agriculture require integrated industrial and agricultural policies that balance food production, environmental quality and public health. No single measure will suffice; a combination of targeted interventions is needed to achieve a safe and truly circular food system.
Read the article in Nature Food: Nutrient management modulates acidification-induced risks to yield and cadmium contents in paddy rice
