I will NOT accept, as some sort of proof, assumptions about IR radiation (Infra = "unperceivable") based on VISUAL PERCEPTION.
"Something known ..." (deleted).
Grass doesn't "emit", anyway. It only reflects... and if there is not much IR to start with, not much will be reflected.
What purposee would this "evening out" serve? You are close to Extended Red IR film.... "Evening out" would only be useful if you are to use conventional black and white, or color film.Yes, and using a complementary colored filter to "even out" the red-leaning response would be a good idea, but I don't know where to find color gels or information on their transmission spectra.
As I've said, try the Tiffen or B&W (preferred) catalogs.