How do legumes contribute to nutrient cycling in pastures?

Legumes play a significant role in nutrient cycling in pastures primarily through the process of nitrogen fixation. This occurs when legumes, such as clover or alfalfa, form a symbiotic relationship with specific bacteria present in their root nodules. These bacteria convert atmospheric nitrogen, which is abundant but not directly usable by plants, into a form that can be absorbed by plants—ammonium or nitrate.

By fixing nitrogen in the soil, legumes enrich the nutrient content, making it available to themselves and other plants in the pasture. This process enhances soil fertility and improves the overall health and productivity of the pasture ecosystem. When legumes die or are grazed, the nitrogen they have fixed is returned to the soil, further contributing to nutrient cycling.

Other options do not correctly describe the primary function of legumes in this context. In particular, while competition with grasses and rapid decomposition can impact pasture dynamics, they do not directly relate to the nutrient cycling mechanism that legumes provide through nitrogen fixation. Additionally, while legumes can have some effects on other nutrients, such as phosphorus, their most significant contribution is related to nitrogen, making them crucial for sustainable pasture management.