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Mineral Concentration of Tall Fescue Genotypes Grown under Controlled Conditions¹

Grass tetany is a disease affecting cattle, sheep, and goats when limited amounts of ultilizable Mg are available. Genetic and environmental considerations on forage Mg are critical if agronomists are to provide forages with low tetany potential. Two genotypes of tall fescue (Festuca arundinacea Schreb.) that differed in inherent Mg concentration were grown in controlled environments to determine if growth temperature and interval between harvests could overcome genetic influences on Mg concentration. Vegetative herbage of genotype B5-62 had Mg concentrations of 0.38 and 0.290%, at the high (25/20 C day/night) and low (17/12 C day/night) temperature, respectively. Genotype B17-42 was inherently low in Mg concentration, and had values of 0.22 and 0.14% for the high and low temperature, respectively. Calcium concentration and the K/(Ca+Mg) ratio were little influenced by the two temperature treatments. Genotype B5-62 was well below the 2.2 (meq/100 g dry matter) critical level for the K/(Ca+Mg) ratio, while B17-42 was above for most treatments. Interval of harvest significantly altered onlv the concentration of K and the K/(Ca+Mg) ratio, with both being the lowest from treatments that were harvested less frequently. It was concluded that genetic control for Mg concentration in these genotypes was sufficiently strong so that genotypes selected for high and low Mg remained relative over two growth temperatures and three harvest intervals.

Key Words: Festuca arundinacea Schreb • Grass tetany • Hypomagnesaemia • Forage quality • Mg • Ca • K

² Associate professor of agronomy, professor of biochemistry, professor of agronomy, and former Agric. Exp. Stn. statistician and presently statistician with USDA/SEA, Univ. of Missouri, Columbia, MO 65211.

Received for publication October 24, 1979.