Methemoglobin has a chocolate brown color, which is a telltale sign of acute nitrate poisoning in cattle. By blocking the transport of oxygen to peripheral tissue, acute nitrate poisoning results in suffocation. Plants take up nitrate in normal growth and developmental processes. During photosynthesis the plant converts nitrates into amino acids and proteins. Nitrate accumulation will occur most readily in the structural components of the plant closest to the ground.
Plant leaves are usually low in nitrate.
Nitrate problems are most common in young growing plants, which are rapidly taking up nitrate to fuel growth. Problems with excess nitrate accumulation may be most common in soils heavily fertilized with poultry or livestock manure. Typically, commercial fertilizers applied at recommended rates are not contributors to excessive nitrate accumulation. Drought stressed plants will rapidly accumulate nitrate after a rainfall. In these situations, the harvesting of suspect pastures should be delayed by several days.