Adding legumes to grassland mixtures can boost biomass production and soil fertility by providing nitrogen through a process called N2-fixation. A study looked at seven different grass-legume combinations and found that red clover and alfalfa were the best at fixing nitrogen, while bird's-foot trefoil and white clover also contributed. The type of grass paired with the legume affected the amount of nitrogen fixed. Fertilization had varying effects on nitrogen fixation among the legumes, and also impacted white clover's nitrogen fixation depending on the grass it was mixed with.