nitrate, weeds, toxicity
Weeds as well as certain crop plants may accumulate higher level of nitrates. Under drought conditions livestock may graze week plants that normally would be avoided. Frequently, weeds like kochia, pigweed, or lamsquarters may be a significant part of forage harvested where precipitation has limited normal forage production. Some weeds are harvested for emergency forage; i.e., kochia has acceptable feed value if harvested early and properly handled. However, frequently weeds in these situations are considerably too mature, unpalatable, and often difficult to cure properly.
Wrage, Leon J. and Deneke, Darrell L., "Nitrate Toxicity from Weeds" (2003). SDSU Extension Extra Archives. 347.