Drought increases forage nitrate and cyanide

Abstract

To investigate drought-associated increases in concentrations of nitrate and cyanide in animal forage, we compared forage nitrate and cyanide in 1986-87 (annual rainfall 33 in) to nitrate and cyanide in a drought (1988 and 1989; annual rainfall 20 and 27 in, respectively). Fifteen to 20% of the nitrate and cyanide samples from 1986-1987 had sufficiently high concentrations to be of concern (3000 ppm nitrate, 20 ppm cyanide as submitted). Only 4-6% of the 1986-1987 samples had concentrations sufficiently high to produce acute respiratory distress (13,000 ppm nitrate, 50 ppm cyanide as submitted). During 1988 sample numbers had more than doubled, suggesting increased concern for the possibility of nitrate or cyanide intoxication and yielding parallel increases in the number of samples with elevated nitrates or cyanides. By 1989, 25-33% of the samples had concentrations of health concern with respect to either nitrate or cyanide, while 14-19% had concentrations sufficiently high to produce acute respiratory signs. Shortages of forage caused by a 2-y drought were further exacerbated by nitrate and cyanide increases in that feed. Future efforts should concentrate on controlling groundwater nitrate and delivery of nitrate to the plant root-systems.