The correct answer to this question is option 3: legumes. Legumes are plants that belong to the family Fabaceae, which includes plants like peas, beans, lentils, and peanuts. These plants have a unique ability to host beneficial bacteria called Rhizobia in their root nodules. Rhizobia have a symbiotic relationship with legumes, where they provide the plants with nitrogen through a process called nitrogen fixation.

Nitrogen is an essential nutrient for plant growth, and legumes can help increase soil fertility by capturing atmospheric nitrogen and converting it into a form that plants can use. This process not only provides nitrogen for the legume itself but also enriches the soil with excess nitrogen, which can benefit other plants growing in the vicinity.

By growing legumes in a field or garden, the soil`s fertility can be enhanced over time. This is because the increased nitrogen levels in the soil promote healthy plant growth, improve soil structure, and provide nutrients for other plants in a crop rotation system.

Option 1 (cereals) refers to grasses like wheat, rice, and corn. While cereals are valuable food crops, they do not have the ability to fix atmospheric nitrogen like legumes.

Option 2 (fiber crops) refers to plants like cotton