Abstract
Magnet Italian ryegrass (Lolium multiflorum L.), HiMag tall fescue (Festuca arundinacea Schreb.), and Mgwell orchardgrass (Dactylis glomerata L.) are the first cultivars bred for higher magnesium uptake (high-Mg) to reduce grass tetany risk for ruminants. The experiment was conducted to evaluate whether magnesium (Mg) uptake efficiency by high-Mg cultivars is limited to specific phosphorus (P) levels, and to optimize P level for individual selections of high-Mg grasses in nutrient culture. The high-Mg cultivars were compared with two existing commercial cultivars viz., Tachiwase and Waseyutaka, of Italian ryegrass, Kentucky-31 (Ky-31) and Fawn of tall fescue, and Akimidori and Okamidori of orchardgrass, respectively. One-month aged seedlings were grown in controlled conditions with three P treatments of 0.1, 1, and 5 mM for 10 days and nutrient contents were determined. Increasing P fertilization increased shoot weights of the grasses. Shoot potassium (K) content of the high-Mg cultivars was lower than the commercial cultivars. In contrast, the high-Mg cultivars were consistently higher in shoot calcium (Ca) and Mg contents when compared to the commercial cultivars, irrespective of species, over P fertilization. While the shoot Mg and Ca contents increased, the K content and K/(Ca + Mg) decreased with increasing P fertilization, regardless of cultivars. Across the P levels, the high-Mg cultivars always showed a K/(Ca + Mg) value lower than 2.2, a safer value for grass tetany in ruminants. Irrespective of grass species, increasing P level reduced the K/(Ca + Mg) and the value became lowest at 5 mM P level. The highest relative range for shoot Mg content was obtained in 5 mM P level for Italian ryegrass (37.6%), tall fescue (30.1%), and orchardgrass (47.9%). Our results indicate the effectiveness of using 5 mM P level for screening high-Mg cool-season grass seedlings.
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