In a five-year trial reported in 2025, scientists mixed discarded oyster shells into acidic farmland; peanut yields rose by up to 37%

Somewhere in a coastal Chinese province, a pile of shells that would otherwise rot in a landfill just helped repair a stretch of tired, sour farmland. In a five-year field trial published in Frontiers in Plant Science in February 2025, researchers ground up leftover oyster shells and mixed the powder into acidic red soil on peanut farms in Jiangxi Province, China. The study found peanut yields increased up to 37% compared to untreated plots, and the soil itself became measurably healthier.

Why farmland keeps getting sour

Soil acidity is a slow, quiet issue. The excessive use of nitrogen fertilizers, together with season-after-season cropping, depletes the nutrients needed to maintain the correct pH. This is not an issue limited to any particular area. The Science study ‘Significant Acidification in Major Chinese Croplands’ found a significant drop in soil pH in key crop-producing areas in China from the 1980s through the 2000s, linked to increased nitrogen fertilizer use and intensive cropping. Acidic soils contain fewer nutrients, inhibit root development, and increase uptake of toxic substances such as aluminum and cadmium. The red soil commonly found in southern China is especially susceptible to acidification. Red soil is naturally acidic, and farmers in the region are seeing lower yields each year.

The experiment: Five years, four treatments, one crop

The team carried out a field trial in Jinxian County, Jiangxi Province, from 2013 to 2018. Peanuts were grown each year in initially acidic soil with a pH of 4.54; neutral soil has a pH of 7. Some plots received only regular chemical fertilizer, the study’s control group. Others received the same fertilizer but with oyster shell powder at three rates: 750, 1500, and 2250 kilograms per hectare. The shells were cleaned and ground into a fine powder, made up of roughly 95% calcium carbonate, and mixed into the soil alongside regular fertilizer.

What actually happened to the peanuts

Yields declined in all plots over the five years, which the authors say is common in continuously cultivated land without crop rotation. However, there was a much slower reduction in the yield in the plots where shells were added compared to the plots that had not been amended with shells. The data showed that yields were higher by an estimated 5.5% to 37%, relative to the control. This is also seen from the soil chemistry. Soil pH increased up to 0.65 units in the plots treated with shells as opposed to the control. This might seem insignificant; however, even a slight change in the pH influences how much the plant absorbs. With reduced acidity, aluminum and hydrogen ions decreased significantly, reaching up to 67% for aluminum.

A side effect worth noting: Less cadmium

The acidic soil makes it easier for crops to absorb cadmium, a toxic heavy metal. The oyster shell powder increased the soil pH and also helped bind cadmium in the soil, so that the amount that can be taken up by plants decreased by as much as about 35% compared to the control, according to the researchers. However, the same treatment that boosted peanut yields also appeared to make the crop safer.

Why this matters beyond one province in China

Soil degradation is a serious issue. The UN Food and Agriculture Organization has warned that land degradation, including acidification, is a growing threat to global food production, one that often drives farmers to even heavier fertilizer use just to hold yields steady, an expensive fix that can worsen the soil problem over time. The utilization of discarded oyster shells can be seen as a means to overcome these challenges. Oyster shells are often discarded without recycling and can become pollutants in coastal areas. Turning them into a soil amendment addresses two problems at once: less waste and healthier farmland.

The takeaway

That does not mean sprinkling shells from a seafood dinner onto a houseplant would do much. The powder in this study was processed before use, and the results were tested in only one soil type in one area. Still, it offers an example of the kind of low-cost, circular thinking farming needs more of. It's not flashy, but it's the kind of low-cost, circular fix agriculture needs more of as farmland keeps wearing thin.