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Root Temperature and Calcium Level Effects on Winter Wheat Forage: II. Nutrient Composition and Tetany Potential

Univ. of Hawaii Branch Stn., 461 W. Lanikaula St., Hilo, HI 96720
U.S. Plant, Soil & Nutrition Lab., Tower Rd., Ithaca, NY 14853

^* Corresponding author.

Wheat pasture poisoning is a metabolic deficiency of Ca, and sometimes Mg, in ruminants. It occurs particularly in the spring, when K and N concentrations in the shoots, and the equivalent ratio of K/(Ca+Mg) in the forages, increase suddenly. To determine the effects of an increased root temperature and four Ca levels on the forage quality of winter wheat (Triticum aestivum L. ‘Centurk’), seedlings were grown under three root temperature regimes (constant 8 °C, constant 16 °C, and increasing from 8–16 °C), in nutrient solutions with four Ca levels (0.2, 0.6, 2.0, and 5.0 mM). Plants grown at 8 °C root temperature had significantly lower Ca, Mg, K, and N concentrations in the shoots, and a significantly lower equivalent ratio of K/(Ca + Mg), compared to those grown at 16 °C. Plants transferred from 8 to 16 °C had significantly increased Ca, Mg, K, and N concentrations in the shoots over time, as levels changed from those characteristic of low root temperature plants to those characteristic of high root temperature plants. Plants transferred from 8 to 16 °C also had an equivalent ratio of K/(Ca + Mg) that increased 1 wk after the transfer, indicating a greater tetany hazard. The doubling in forage K and N concentrations, and the increase in the equivalent ratio of K/(Ca+Mg) as root temperatures increased from 8 to 16 °C, are similar to those found in field-grown plants at the time of tetany for grazing beef cattle. Thus, root temperature could be a key environmental factor involved in tetany, modifying the nutritional quality of winter wheat.

Received for publication October 24, 1988.