The black soils of Peninsular India, also known as regur or black cotton soils, are known for their fertility and agricultural productivity. Let`s dissect each option to understand why option 4 is incorrect.

Option 1: Black soils are indeed rich in iron, lime, and potash. These minerals contribute to the fertility of the soil and support the growth of crops.

Option 2: Black soils have a high retention capacity for moisture. They can retain water for extended periods, which is beneficial for crops during dry periods.

Option 3: Black soils are fertile and well-suited for growing numerous crops, including sugarcane. The deep and well-drained nature of the soil helps in the growth of sugarcane and other crops.

Option 4: This option is incorrect. Black soils are not naturally rich in phosphorus. While they are high in organic matter, phosphorus content is relatively low. However, farmers can address this deficiency by adding fertilizers that contain phosphorus to enhance agricultural productivity.

In conclusion, the correct answer is option 4 because black soils of Peninsular India are not naturally rich in phosphorus. Farmers need to supplement the soil with phosphorus-based fertilizers for optimum crop growth.