Factors affecting the concentration of Zn, Fe and Mn in herbage from organic farms and in relation to dietary requirements of ruminants

Summary

To obtain a general picture of the herbage zinc, iron and manganese concentrations and their relation to dietary requirements of ruminants on organic farms, we analysed soil and herbage samples from four regions in Norway. The soil median Zn, Fe and Mn concentrations were 0.18, 13 and 0.84 mg/L, respectively. The herbage median (10th-90th percentile) Zn, Fe and Mn concentrations (mg/kg) in herbage in the first cut were 19 (14-34), 50 (36-88), 34 (22-86) and in the second cut 21 (16-37), 84 (52-171) and 66 (36-205), respectively. The results of mixed model analysis of herbage Zn, Fe and Mn indicate that soil pH, soil texture, soil mineral concentration and botanical composition are the most influencing factors. We conclude that Zn, Fe and Mn did not limit plant growth, and that the herbage concentrations except for Zn, were sufficient to meet the dietary needs of ruminants on organic dairy farms.