Browning in our hay fields
First thing is to determine if plants from brown areas are alive or dead. If dead, then it is possible to have insect damage or acid soil issues but the acidity would have to be pretty low. Have you dug up any plants to look at the crowns and roots? There has been a lot of winter cutworm damage so that might be a possibility.
See my web page for info on the cutworm,
You can contact me via phone at 503-931-5163