Alfalfa and grass (IMAGE) American Society of Agronomy Caption Some of the research pastures included warm-season old world bluestem grass (left) mixed with legumes including alfalfa (purple blooms, center) and yellow sweetclover (yellow blooms, lower left). The legumes provide an organic source of nitrogen to the grasses and microbes, as well as a source of protein for grazing cattle in the pastures. Credit Lindsey Slaughter Usage Restrictions For use with this story only. License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.