Question

why were the turnips and clovers grown by farmers ?

Answer 1

They believed planting crops like clover and turnips improves the soil and makes it more fertile. It is known to be a good fodder crop for cattle. They increase the nitrogen content in the soil which is important for the growth of the plants and crops. And when the nitrogen is restored turnip and clover make the soil fertile once again after the soil reduces its fertility by cultivation again and again. 

Answer 2

turnip and clovers were grown by farmers to increase the fertility of soil.