Making the Crusades possible: the agricultural revolution
The soil of northern Europe was too dense and damp to be plowed efficiently with the scratch plows of the day to produce much past subsistence. In order to cut the heavy soil, the heavy plow was invented which included a cutter, plowshare, and wheels and was initially drawn by oxen. The need for speed and horse power, as horses pulled two hours longer and faster, lead to the invention of the horse collar which solved the problem of the oxen yoke which choked the horse. The hooves of horses did not fare well in the damp earth, unlike oxen, which lead to the use of horse shoes.
Oxen could survive largely on hay, but horses needed vegetable protein such as from grain and legumes (beans). The additional protein in farmers diets lead to increased energy in the people in the area. Since legumes contain symbiotic bacteria called Rhizobia, they were found to restore nitrogen to farmland. Crop rotations changed from fallow and wheat to fallow, wheat, and legumes, a change to three crop rotation which also extended the productive use of the land.
This text consists of slightly edited quotes from the blog The Cistercian Connection by Gordon S Fowkes. The illustration is from the same source.