Why did farmers start growing turnip and clover in England?

The European peasants had discovered that planting crops like clover and turnip improved the soil and made it more fertile. Turnip was a good fodder crop for cattle. These crops had the capacity to increase the nitrogen content of the soil. Nitrogen was important for crop growth. Cultivation of the same soil over a few years depleted the nitrogen in the soil and reduced its fertility. By restoring nitrogen, turnip and clover made the soil fertile once again.