The name of the cycle that describes the conversion of nitrogen in the soil is called the nitrogen cycle. This cycle involves several processes, including nitrogen fixation, nitrification, and denitrification. Nitrogen-fixing bacteria convert atmospheric nitrogen into forms usable by plants, while nitrification involves the conversion of ammonia to nitrates. Ultimately, denitrifying bacteria reduce nitrates back to atmospheric nitrogen, completing the cycle. The nitrogen cycle is essential for maintaining soil fertility and supporting plant growth, hence playing a critical role in ecosystems.