Don’t burn straw, feed it to earthworms

A woman pounds rice stalks at Ahero Irrigation scheme in Kisumu on January 22,2019. Researchers say that instead of burning the stalks, which take long to decompose, they should be fed to earthworms. PHOTO | ONDARI OGEGA

When rice is harvested, the straw left behind is usually burnt, causing the emission of greenhouse gases (carbon dioxide and methane) and black carbon, which has a negative effect on climate.

Instead of burning, scientists say that the straw could be fed to earthworms, helping decompose it faster, and enriching the soil with organic matter to increase its fertility in the process.

In a study described in the European Journal of Soil Biology, researchers collected soil samples in three rice-growing regions, which lacked earthworms, in Russia.

The researchers introduced earthworms in confined settings mimicking natural conditions and studied the ratio between the emission of carbon dioxide, methane and organic carbon, and the type of soil, presence of straw and the number of earthworms in it.

The researchers found that rice straw increased carbon dioxide emissions by a factor of three, but the ratio between emitted carbon dioxide and the number of earthworms varied depending on the type of soil collected from the different regions.

When bound with the soil, organic carbon improves fertility and erosion resistance, but when burnt, it produces carbon dioxide or black carbon.

“We’ve found a way to efficiently process rice straw instead of burning it which is currently the most common practice worldwide.

“Along with increasing sustainability and climate safety of rice growing, it reduces the risks (for the environment and mankind) associated with agricultural burns as causes of fires and atmospheric pollution, including with carcinogenic substances,” said researcher Andrey Zaitsev.

“Moreover, adding earthworms to soils will increase the quality, fertility, and soil health of the fields and reduce the risk of erosion due to binding with organic substances,” he added.