Status of Iron, Manganese, Copper, and Zinc of Soils and Plants and Their Requirement for Ruminants in Inner Mongolia Steppes of China

Abstract

The availability of heavy metal micronutrients and their distribution in soils and plants as well as their requirements for grazing animals are important when assessing the environmental quality and nutritive status for ruminants of a given area. The mean available copper (Cu), zinc (Zn), and manganese (Mn) contents of all soils were respectively 1.20, 1.60, and 3.38 g kg−1 of calcareous soils in the Inner Mongolia steppe of China. The heavy metals content of the chernozem soil were usually greater than those of other soils, whereas their contents in plants, however, were usually smaller than those in plants from other soils. It means that the heavy metal bioavailability in the chernozem soil is relative low. Positive significant correlations between available Cu, Zn, and Mn and organic carbon, total nitrogen and clay contents, and between available Cu and Zn and between available Zn and Mn in soils were observed. On the other hand, negative significant correlations between heavy metals and pH were found. The results of stepwise regression analysis showed that the parameter organic carbon and clay are the most important variables. Available Cu, Zn, and Mn contents increased with increasing organic carbon and clay. Means and ranges of iron (Fe), Mn, Cu, and Zn in plants of the five soils were 14.6–91.5, 3.1–5.4, 0.8–2.3, and 1.5–2.2, respectively. Therefore, all plant samples were considered severely deficient in Fe, Mn, Cu and Zn for all ruminants. The availability of micronutrient heavy metals in soils to plants and to grazing animals in plants deserves further studies in this region. The Fe, Mn, Cu and Zn contents in feces of grazing sheep averaged 125.3, 16.4, 4.8 and 6.2 mg kg−1. In the natural grassland, animal manures, therefore, may be an important heavy metals source.