Phosphorus fertilization affects cation balance in cool-season grasses associated with grass tetany

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.