Researchers identify low-cost method to remove heavy metals from soil while increasing rice yields

Yaser Rebukh, Associate Professor at the Patrice Lumumba Peoples' Friendship University of Russia (RUDN University), together with colleagues from Tanta University in Egypt, has demonstrated that the aquatic fern Azolla can simultaneously improve soil fertility, reduce toxic heavy metal content and increase rice yields. This was reported on the website of the RUDN University, a partner of TV BRICS.

Azolla is a small aquatic fern that floats on the surface of freshwater bodies. Living in symbiosis with microscopic algae, it absorbs nitrogen from the atmosphere and rapidly accumulates biomass. This ability makes it an ideal natural fertiliser. Another valuable property of Azolla is its capacity to extract heavy metals from the soil.

The researchers planted rice in pots containing soil contaminated with copper, zinc and lead. During the experiment, they applied different amounts of fresh Azolla used as green manure, Azolla compost and mineral fertilisers. As a result, the concentrations of bioavailable zinc and copper in the soil fell to safe levels.

The study found that rice yields increased by almost 64 per cent compared with the control pots where Azolla had not been applied. In addition, the organic matter content increased (by up to 33 per cent under the best treatment), the soil's cation exchange capacity – its ability to retain nutrients – improved, and the supply of nitrogen, phosphorus and potassium to the plants increased. A reduction in soil acidity was also observed.

"We have shown that the simple and readily available aquatic fern Azolla can solve several problems at once: increasing rice yields, improving soil health and reducing heavy metal contamination. This is particularly important for developing countries, where farmers cannot afford expensive soil remediation methods. Our work supports the principles of the green economy and circular agriculture – we take waste (Azolla biomass) and turn it into a valuable fertiliser and phytoremediation agent," Rebukh said.

According to the researchers, the use of Azolla is a natural, safe and low-cost way to produce clean rice without harming the environment. In addition, Azolla helps reduce the greenhouse effect by capturing carbon and lowering methane emissions from rice fields.

The scientists plan to continue combining Azolla with other hyperaccumulator plants or microorganisms in an effort to remove lead from the soil, which could not be eliminated during the experiment.