I am curious. I have been doing the Equi Tech 601 test for my hay analysis. It does not measure nitrates. I live in South Central Ky and we too have Johnson Grass in every hay field. We try and bale 1st cutting before it really starts growing but it's impossible to guarantee. We lost half our 1st cutting this past season and had to bale 2nd cutting which had a lot of Johnson Grass in it since it thrives in the warmer months. 

I have NOT had issues with my IR mare since tightening up her diet  (knock on wood)  but now I am wondering if in 2020 should I begin to add a nitrate test for that? I was initially concerned of being higher in sugar and starch because it is in the sorghum family.