The essential nature of certain minor elements for plant nutrition

The available evidence makes it quite clear that small amounts of boron and manganese are essential to the growth and health of many, if not all, species of plants. Copper and zinc have also been found to be necessary in many cases, though up to the present it is uncertain whether this need is universal. Apart from these four elements, isolated cases only of improvement due to traces of other minor elements have as yet been established. It may be, however, that specific elements are necessary for specific plants, and it is possible that the conclusive evidence already obtained with boron and manganese may further the opening of a wide field of investigation which may lead to results of far-reaching importance from scientific and economic standpoints