What change in agricultural practice allowed a family to leave serfdom and become tenant farmer instead?

Families were aloud to leave serfdom and become tenant farmers because of the large improvements made in agricultural production. Farmers gradually started to consolidate their small strips of land into one larger field, allowing them to produce larger harvest. Instead of growing a small amount of many different kinds of crops, they concentrated on what they could best grow. Farmers also began to improve the soil. They also benefited from the new products from the Americas