The removal of excess water from the sub-soil is known as

The correct answer is "drainage". Drainage is the removal of excess water from the sub-soil. Excess water in the sub-soil can be harmful to plant growth as it can cause waterlogging, which reduces the amount of oxygen available to the plant roots. Drainage is done by providing channels or outlets through which the excess water can flow out of the soil. This helps to improve soil aeration, soil structure, and root development, which ultimately leads to improved plant growth and higher yields. Drainage can be achieved through various methods, such as surface drainage, subsurface drainage, and vertical drainage.