Influence of Soil Moisture and Plant Cultivar on Cation Uptake by Wheat with Respect to Grass Tetany

Several researchers' report that the incidence of grass tetany is most severe when soils are nearly water-saturated. This report prompted three growth-chamber studies to determine the influence of soil moisture and wheat cultivar on K⁺, Ca⁺⁺, and Mg⁺⁺ ion uptake and the estimated tetany potential of wheat forage. Hard red winter wheat (Triticttm aestivum L. ‘Centurk’, ‘Eagle’, and ‘Newton’) was grown in pots containing 2 kg ofEudora loam (Fluventic Hapludoll) soil. Two soil moisture levels (13 and 27 volume %) were maintained by weighing the pots and watering daily. Final pot weights were increased periodically to account for plant growth. In samplings where cation concentrations were significantly different, K concentrations in leaf, crown, and root tissue from plants grown at 27% moisture decreased 0.10%, increased 0.29%, and increased 0.58% respectively; Ca concentrations decreased 0.12To, 0.05%, and 0.35%, respectively; Mg concentrations decreased 0.01%, 0.02%, and 0.06%, respectively. The equivalent ratio K/(Ca + Mg) in the three plant parts increased 0.49, 0.53, and 0.92, respectively. The average Mg concentration in the root tissue (0.22%) was higher than in either the crown (0.16%) or leaf (0.18%) tissue, indicating that among other factors contributing tO low forage Mg, there might be translocation mechanisms that limit the taovement of Mg into leaf tissue. Analysis of non-vernalized wheat tissue showed significant cultivar differences. Average K concentrations in Eagle wheat 16.29%) were greater than in either Newton or Centurk wheat (5.94 and 5.52%, respectively); Ca and Mg concentrations in Eagle wheat (0.823 and 0.193%) were lower than Ca and Mg concentrations in Newton and Centurk wheat (0.980 and 0.222%; 0.940 and 0.217%, respectively). These differences in cation composition resulted in an average equivalent ratio in Eagle wheat of 2.80 compared to 2.27 and 2.28 in Newton and Centurk wheat, respectively. Cation concentrations in the samplings of vernalized wheat showed no significant cultivar differences; however, average equivalent ratios for Newton, Centurk, and Eagle wheat (2.56, 3.00, and 3.47, respectively) were significantly different. This result indicated that Eagle wheat would be a more tetany-prone forage than either Newton or Centurk wheat. These studies have shown that soil moisture content, cultivar, and possibly translocation mechanisms influence the cation concentrations of wheat forage. They also indicate that perhaps a breeding program could be developed to produce wheat cultivars that have a more balanced cation composition and a lower potential for inducing grass tetany in grazing cattle than those now grown.