The correct answer is: A. Khadar soil
Khadar soil is a type of alluvial soil that is found in the Indo-Gangetic plains. It is a light-textured soil that is rich in organic matter and nutrients. Khadar soil is well-drained and has a good water-holding capacity. It is suitable for growing a variety of crops, including rice, wheat, sugarcane, and vegetables.
Heavy and very heavy soil is a type of soil that is high in clay content. It is a dense soil that is difficult to work with. Heavy and very heavy soil is not well-drained and has a poor water-holding capacity. It is not suitable for growing most crops.
Bangar soil is a type of soil that is found in the semi-arid regions of India. It is a light-textured soil that is low in organic matter and nutrients. Bangar soil is poorly drained and has a poor water-holding capacity. It is not suitable for growing most crops.
Piedmont soil is a type of soil that is found in the foothills of the Himalayas. It is a well-drained soil that is rich in organic matter and nutrients. Piedmont soil is suitable for growing a variety of crops, including wheat, maize, and vegetables.
In conclusion, the fertility of Khadar soil can be increased by various organic and chemical fertilizers.