Linked from
The 7 pages that link to Threshing, each with the reason it gives.
HarvestRelated: Grain harvest often requires separating kernels from the cut plants.
StrawRelated: Threshing frees grain from the crop material that becomes straw.
SwatherRelated: Swathed grain is later picked up and threshed, often by a combine.
Reaper-binderRelated: The sheaves produced by the binder are gathered for threshing.