Differences in mineral concentration among diploid and tetraploid cultivars of rhodesgrass (Chloris gayana)

Abstract

Mineral composition of a range of rhodesgrass cultivars was measured to assess if levels were suitable for cattle growth. Leafy regrowth of 11 rhodesgrass cultivars and lines was analysed for a range of elements in 2 replicated field experiments near Gympie in southern Queensland. Experiment 1 comprised 2 diploid and 2 tetraploid cultivars, while 7 diploids and 3 tetraploids were compared in experiment 2.Overall, the tetraploids had higher nitrogen (N), potassium (K), calcium (Ca), and magnesium (Mg) concentrations but lower sodium (Na) and boron (B) concentrations than the diploids. Concentrations of potassium (P), copper (Cu) and aluminium (Al) for the 2 groups were similar and showed no significant cultivar differences. Results for sulfur (S), zinc (Zn) and iron (Fe) varied between experiments, either with no significant ploidy and cultivar differences or with higher concentrations in the tetraploids (S in experiment 2, Zn in experiment 1). The tetraploids had significantly higher concentrations of Mn in experiment 2. The Na concentration found in cultivar Boma was lower (0.02%) than the other cultivars in experiment 2. Similarly, cultivar Samford in experiment 1 had a lower Na concentration than the other 3 cultivars. Both Boma and Samford, however, had the highest Mg concentrations in their respective experiments. K/(Ca+ Mg) equivalent ratios in the 2 experiments were in the range 0.40-1.50. This is well below the accepted critical value of 2.2 above which grass tetany in ruminants could become a problem.