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Soil and Plant Parameters Associated with Grass Tetany of Cattle in Kansas¹

Few researchers in the United States have attempted to correlate the soil and plant parameters related to the grass tetany problem. To investigate those correlations, we identified areas in Kansas where outbreaks of grass tetany had been diagnosed, and collected forage and soil samples from fields where grass tetany had occurred in grazing cattle. Forage samples were analyzed for K, Ca, and Mg; soil samples were analyzed for pH, exchangeable K, Ca, and Mg, cation exchange capacity and cation activities. Forage K, Ca, and Mg concentrations and equivalent ratios (Mg/K) were correlated with soil-test parameters and soil exchangeable Mg/K ratios. Chemical analyses indicated forage samples had enough K and Ca for proper nutrition of lactating beef cows, but Mg concentrations were generally less than the 0.2% level essential to maintain normal blood serum Mg concentrations. Low Mg concentrations in the forage resulted in the equivalent ratios [K/(Ca+Mg)] that exceeded 2.2. The soil was fairly high in K and adequate in Ca. Magnesium saturation of the surface and the subsoils ranged from 3 to 45% and, except in a few locations, a response to fertilizer Mg would be highly unlikely. Ion activities showed that Ca was the predominant cation in the soil; Mg activity was about one-third that of Ca and twice that of K. Potassium activity was most closely correlated to the forage K concentration in wheat (Triticum aestivum L.), whereas, Mg concentrations in wheat forage were most highly correlated with the subsoil Mg saturation percentages and the subsoil exchangeable Mg/K ratio. Magnesium concentrations in fescue (Festuca arundinacea Schreb.) and bromegrass (Bromus inermis Leyss.) correlated most highly with surface soil Mg activity and exchangeable Mg measurements. The correlation coefficients indicated that none of the soil-test parameters were entirely successful in identifying soil characteristics important in the tetany syndrome. We feel that in Kansas, environmental and management factors are more important in the incidence of grass tetany than the soil's characteristics.

Key Words: Hypomagnesaemia • Forage quality • Soil-test correlations • K • Ca • Mg • Bromus inermis Leyss. • Festuca arundinacea Schreb.

² Soil scientist, Coastal Plains Soil and Water Conserv. Res. Ctr., USDA-SEA-AR, Florence, SC 29502, (formerly research assistant, Dep. of Agronomy, Kansas State Univ.) research soil chemist; soil fertility research agronomist, Dep. of Agronomy, Kansas State Univ.; and soil scientist, U. S. Plant, Soil, and Nutrition Laboratory, USDA-SEA-AR, Ithaca, NY 14853, respectively.

Received for publication January 26, 1979.