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Hydrocyanic Acid Potential in Several Sorghum Breeding Lines as Affected by Nitrogen Fertilization and Variable Harvests¹

Many sorghum (Sorghum bicolor (L.) Moench) breeding lines have not been evaluated for inherent potential hydrocyanic acid (HCN-p) levels under field conditions. Additionally, levels of HCN-p remaining in sorghum stover used for animal grazing after grain harvest needs elucidation as well as N effects on lines shown to be inherently low in HCN-p.

Fifteen entries, including 13 sorghum lines, one sweet sorghum, and one sudangrass (Sorghum sudanense (Piper) Stapf), were evaluated for differences in HCN-p, influence of N fertilization, and date of harvest. The entry Tx7000 was consistently low in HCN-p at all harvest dates and only exceeded the "threshold of danger" (200 ppm) at the preboot stage. This level is considered to be an approximate value at which HCN may become toxic to ruminant animals. The highest ranking entry was SC0599-6, a Rio selection, which exceeded the 200 ppm level at all stages of harvest employed. Even in entries inherently low, added N increased HCN-p, which supports the theory that caution must be exercised when growing cultivars reportedly low in HCN-p, especially when N fertilizer is applied.

As expected, HCN-p tended to decrease with plant maturity. After physiological maturity of the grain, panicles were removed and leaf blades sampled 8 days later. Two of the entries still retained HCN-p in excess of 200 ppm, indicating a need to exercise caution with some cultivars when allowing cattle to graze stover after grain harvest.

Key Words: Prussic acid • Sorghum stover • Dhurrin • Sudangrass • Sorghum bicolor • S. sudanense

² Professor and associate professor, respectively, Dep. of Soil and Crop Sciences, Texas A&M Univ., College Station.

Received for publication May 29, 1979.