Researchers at Cornell University are looking at ways to help breed better cover crops, also known as green manures, that could help farmers in their quest to grow crops in the most sustainable way. Their results were published in Crop Science, a publication of the Crop Science Society of America.

Katherine Muller and her team are working on strategies to measure nitrogen fixation in breeding programs for two common cover crops: crimson clover and hairy vetch. Both crops can pull nitrogen from the air to help them grow. This is called nitrogen fixation.

"Green manures are crops used to improve soil fertility," says Muller. "They help the soil by adding nutrients. We look at legumes, which bring nitrogen into the soil due to their symbiotic relationship with bacteria."

The use of legume green manures has been around for thousands of years. However, after the 1950s, chemical fertilizers became the main nitrogen source for farmers in developed countries. This is because two scientists, Haber and Bosch, found a way to pull nitrogen from the air, and make chemical fertilizer.