From my post some time ago I summarized the 1000-year medieval period marked by revolutions in agriculture, including:

• invention of mortar board plow

• inventions in animal harnessing leading to productivity leaps

• shift to 3 field tillage

• development of varied cereal crop types

• expansion of water-driven mills

• expansion and enforcement of exclusive rights of nobility to hunt

• development of fish ponds

(In fact all of the above were achieved by 1200 CE if not earlier.)

I then expanded on some for a followup question:

invention of mortarboard plow

Roman sole plows were effective at turning light mediterranean soils that needed only shallow planting - these plows were not very productive in the hard, dense clay soils of the north. The mortarboard plow invented in the early middle ages dug and turned soil deeper, allowing nutrients to be turned over for productive planting over generations instead of rapid exhaustion of topsoil.

inventions in animal harnessing leading to productivity leaps

The regular horse collar harness only allows lightweight pulling as it compresses windpipe. The chest harness is said to have come from the Asia to Europe by the 9th c - it allowed different distribution of load on the horse which made it easier to pull heavier loads under more resistance. This lead to increased efficiencies in plow-based production (horses are faster than oxen, and thus more field could be put to cultivation with the same power input) and to the movement of agricultural products via heavier wagons (commodities could be transported further, faster)

shift to 3 field tillage

Three field rotation tillage, evidenced as developing in the Carolingian period, allowed one field to go fallow every three years while the other two fields maintained crops. In effect this was letting the fields regenerate nutrients instead of exhausting them - this was possible because of expansion of agriculture use of the landscape (turning forests and rock strewn landscapes into productive crop lands)

development of varied cereal crop types

With the 3 field rotation tillage, different crops could be planted, and experimentation with different season crops could occur (ie winter grains)

expansion of water-driven mills

The tremendous amount of non-mountainous rivers and streams in the UK and western Europe allowed very fast expansion of water-driven technology by 1000; this contrasts to Byzantine lands at the time which, although they did have water mills, they just weren't as common - apparently because rivers and streams tended to be in mountainous areas with less crop land.

The water driven mills were used for milling grain, and also fulling wool - which became an economy-catalyzing industry by the high middle ages.

See also this thread for more facets of changes in medieval agriculture.