Fertile soil is one which

Fertile soil is soil that contains all the essential plant nutrients in suitable proportions to support good plant growth. These essential plant nutrients include nitrogen, phosphorus, potassium, calcium, magnesium, and sulfur, among others. When these nutrients are present in the soil in the right amounts, they help plants grow healthy and strong, producing high yields of crops. Therefore, fertile soil is necessary for successful agriculture and plant growth. The other options - well-aerated, easily drained, and capable of producing good cowpea harvests - are also important characteristics of fertile soil but do not fully capture the complete definition of fertile soil.