Case Study: Regional assessment of mineral element concentrations in Idaho forage and range grasses

The objective was to quantify forage mineral concentrations in Idaho and evaluate changes due to seasonality and irrigation. Forage was sampled on rangeland and irrigated pastures in summer and fall from 35 locations in 9 counties and analyzed for Ca, P, K, Mg, S, Na, Zn, Fe, Mn, Cu, Mo, Co, and Se. Statistical analysis was by pasture type using mixed model repeated measures with fixed effects being county, season, and county × season. Location within county was a random effect. Samples were also analyzed by soil type with type of forage, season, and type × season as fixed effects and location within soil type as the repeated random effect. The macrominerals P, Mg, and Na were deficient in rangeland forage, and Na was deficient in irrigated forage. Potassium was deficient on fall rangeland. Deficient trace minerals for both pasture types were Cu, Se, and Zn. Cobalt was deficient on both types of summer pasture. Antagonistic minerals were Mo and Fe. Forage macromineral concentrations declined (P < 0.05) from summer to fall for P and K on irrigated pasture and for P, K, and S on rangeland. Iron increased (P < 0.0005) from summer to fall on both types of pasture. Clay loam soils had greater (P < 0.05) Fe and Co and less Se than did sandy loam soils. Forage sampling confirmed the importance of obtaining duplicate samples for laboratory analyses, especially for Se. Pairing a customized mineral mix to forage deficits is a plausible management option for beef cattle operations in Idaho.