Carbon sequestration is the process of capturing and storing atmospheric carbon dioxide. It is one method of reducing the amount of carbon dioxide in the atmosphere with the goal of reducing global climate change.

Contour bunding is a method of farming that is practiced on the slopes of hills. It helps in reducing soil erosion and increasing the organic matter content in the soil. This in turn helps in carbon sequestration.

Relay cropping is a method where a second crop is sown before the first crop is harvested. While it helps in maintaining soil cover and can contribute to carbon sequestration, it is not as direct a method as contour bunding or zero tillage.

Zero tillage is a way of growing crops from year to year without disturbing the soil through tillage. It increases the amount of water that infiltrates into the soil and increases organic matter retention and cycling of nutrients in the soil. This helps in carbon sequestration.

Therefore, all three practices help in carbon sequestration/storage in the soil.