Why harvest index is more in cereals than legumes?

The harvest index, which is the ratio of grain yield to total biomass, is typically higher in cereals than in legumes due to the inherent growth strategies and resource allocation of these plants. Cereals, such as wheat and rice, are bred for high grain production, resulting in a greater proportion of their biomass being allocated to grain. In contrast, legumes invest more in vegetative growth and nitrogen-fixing nodules, which can lead to lower grain yields relative to their total biomass. Additionally, the reproductive strategies of cereals favor the production of larger amounts of grain, further enhancing their harvest index.