高等植物生长和繁殖所必需的十六种元素中有七种是微量元素:铁、铜、锌、硼、钼、锰和氯。土壤中微量元素亏缺的一个显而易见的原因是土壤由之演化而来的岩石或者土壤母质中缺乏营养物质。所以土壤类型常可指出潜在缺素的可能性。海洋沉积土含有足够浓度的可用硼,而在有机质含量很低的粗质土壤中却常常缺硼。碱质土壤时常缺铁,土壤 pH 为8或8以上时尤其严重。由于世界上多达三分之一土壤 Seven of the sixteen elements necessary for the growth and reproduction of higher plants are trace elements: iron, copper, zinc, boron, molybdenum, manganese and chlorine. One of the obvious causes of trace element deficiency in soils is the lack of nutrients in the rock or soil parent material from which the soil evolved. So the type of soil can often point out the possibility of potential deficiency. Marine sediments contain sufficient concentrations of available boron, while boron is often deficient in coarse soils with low organic matter content. Alkaline soils are often deficient in iron, especially when soil pH is 8 or above. As much as a third of the world soil