A few years ago we rented some irrigated corn stalks from a weekend farmer who did things half-a$$ed.  After about a week we found 10 head dead on top of a rocky knob where the corn was not much.  Vet confirmed it was nitrate poisoning.  Come to find out that he accidently double fertilized in that area.  Since there was not much corn there on the hill what was there had absorbed an excess amount of fertilizer.  It had snowed the night before so the cows had gone to the hill to graze as the wind had blown the snow off in that area.  After that we get stalks tested if we are not sure of the history and in particular get the stalks from a poor spot in the field.  On our own land we variable rate fertilizer so no concern about this situation.  Regardless it is not a bad idea to get the stalks tested for nitrates just to be safe.  Fraction of the cost of a bunch of cows.