Effect of basic cation saturation ratios on the Mg, K and Ca content of annual ryegrass (Lolium multiflorum L.)

A pot experiment was carried out in a greenhouse to determine the optimal percentage of exchangeable Ca, Mg, and K in the CEC for improving the yield and favourable mineral composition of annual ryegrass plants. The experiment comprised 13 fertilization treatments with various basic cation saturation ratios in soil. Correlation and regression analyses revealed that the K content of ryegrass was influenced mainly by the percentage of K in the soil’s exchange complex, but was far less affected by the percentage of saturation with Ca and Mg. Higher saturation of the CEC with Mg and Ca had a negligent effect on limiting the “luxury” uptake of K by grasses. The Mg content of plants grown for green forage was significantly more influenced by the Mg : K ratio in soil than by saturation levels of Mg, which suggests that K has a strong antagonistic effect on the Mg uptake. An increase in the percentage of saturation with Ca led to a progressive increase in the Ca content of ryegrass. An increase in the percentage of saturation with Mg or K had the opposite effect. The K : (Ca+Mg) ratio in ryegrass was most highly correlated with the percentage of the CEC occupied by K. When the percentage of the CEC occupied by K exceeded 5%, the K : (Ca+Mg) ratio of the first cut was higher than 2.0, which points to undesirable proportions of those cations in ryegrass forage. To maximize the yield of annual ryegrass with optimal mineral composition, the soil exchange complex should be occupied by 50-60% Ca, 8-12% Mg and 4-5% K, and the Mg : K ratio in soil should be maintained at 2-3 : 1.