The soil in question has been depleted of nitrogen due to the repeated growth of wheat. Nitrogen is an essential nutrient for plant growth and plays a vital role in the formation of proteins and DNA. When wheat is grown continuously on the same soil, it depletes the nitrogen levels because the plants take up the available nitrogen to support their growth.

To enrich the soil again with nitrogen, it is recommended to grow plants that have a high nitrogen-fixing capability. Nitrogen-fixing plants have a symbiotic relationship with certain bacteria in their root nodules, which convert atmospheric nitrogen into a form that can be utilized by plants.

Option 1 suggests growing soybean or alfalfa, both of which are leguminous crops known for their nitrogen-fixing ability. These plants have nodules on their roots that house nitrogen-fixing bacteria, allowing them to convert atmospheric nitrogen into a usable form for the plant.

Option 2 suggests growing soybean or eucalyptus, but eucalyptus is not known for nitrogen fixation, and therefore, it would not be the best choice for enriching the soil with nitrogen.

Option 3 suggests growing alfalfa or maize. While maize is a commonly grown cereal crop, it does not have the same nitrogen-fixing ability as