Nitrate levels are therefore highest in plants at night and early morning when the nitrate-reducing enzymes are least active. Cool, cloudy days enhance nitrate formation in plants because these conditions inhibit the enzyme nitrate reductase, allowing nitrate to accumulate in the plant. Drought conditions, acidic soils, and soils deficient in sulfur, phosphorus, and molybdenum result in accumulation of nitrate in plants. Nitrate levels can vary considerably in plants depending on the plant species, stage of growth, water and organic matter content of the soil, and the application of nitrate fertilizers. Many common weeds and crops have the potential to accumulate nitrate under specific growing conditions.

When consumed, these nitrate fertilizers cause severe gastrointestinal irritation, colic, and diarrhea. Nitrate fertilizers are highly toxic chemicals capable of causing fatal poisoning in ruminants and horses when accidentally eaten. The potential for nitrate poisoning increases when the drinking water also contains high levels of nitrates. Plant nitrates are rarely a problem for horses because their digestive system does not readily convert nitrate to toxic nitrite. This greatly reduces the oxygen-carrying capacity of blood, and the animal suffers from oxygen starvation of the tissues. Consequently, when ruminants consume plants high in nitrate, excess nitrite formed in the rumen enters the bloodstream where it converts blood hemoglobin to methemoglobin.

The reduction of nitrate to nitrite occurs much more rapidly in the rumen than the reduction of nitrite to ammonia. In the rumen, ingested nitrate is broken down to nitrite and then undergoes further degradation to ammonia, which is used to form microbial proteins. (Print Friendly PDF)Īlthough poisoning from the various forms of nitrate is referred to as nitrate poisoning, the nitrate ion itself is relatively nontoxic. Respectively, Rangeland Scientist, Linebery Policy Center for Natural Resource Management and Extension Veterinarian, Department of Extension Animal Sciences and Natural Resources, New Mexico State University. Allison and John WenzelĬollege of Agricultural, Consumer and Environmental Sciences, New Mexico State University

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