"Knifed hay" typically refers to a method of harvesting hay using a piece of equipment known as a hay cutter or hay knife. This equipment has sharp blades that cut through the standing hay, effectively harvesting it. The cut hay is then typically left in the field to dry and cure before being collected and baled for storage or livestock feed.
The term "knifed hay" is often used to describe this process and the result of using a hay cutter to harvest hay. It's a common method in agriculture, especially in areas where hay is a significant part of livestock feed.