Response of plants to boron, copper, and manganese

Studies were made of the influences of boron on the growth and boron content of lettuce; of kaolin on the growth and manganese content of buckwheat in quartz sand cultures; of copper, manganese, and zinc on onions and sweet clover grown on peat in pot cultures; and of the influence of these elements on onions and potatoes grown on peat soils in the field. The plants grown on peat soils, as well as the soils themselves, were analyzed for manganese. The results obtained may be summarized as follows: 1. In quartz sand cultures, lettuce was unable to continue normal growth or produce a second growth of leaves unless boron was added. Plants showing the typical boron-deficiency symptoms produced new leaves and resumed normal growth after boron was supplied. Milorganite (activated sludge containing some boron) made possible nearly normal growth and increased the boron content of the lettuce Boric acid prevented the appearance of all deficiency symptoms and doubled the boron content of the plants. Pyrex glass was also a good source of boron. 2. The application of kaolin to quartz sand cultures stimulated the growth of buckwheat and increased its content of manganese, but it inhibited seed production. Extraction of the sand and kaolin with dilute acid indicated that the manganese was obtained from the sand and not from the kaolin. The kaolin probably stimulated the feeding power of the buckwheat. The addition of manganese to the sand increased the yields appreciably. 3. Applications of copper and manganese to peat soils in pot cultures increased the growth of onions and sweet clover and the manganese content of the leaves. Some evidence was obtained that copper and manganese affected the relative growth of bulbs and tops and the maturation of the plants as well as the rate of growth 4. Applications of copper, manganese, and zinc increased the yield of potatoes grown on peat soils in the field. The tubers of potatoes and the bulbs of onions grown on peat treated with copper appeared to be considerably better in quality than those not so treated. 5. Extraction of the soils with dilute acid showed that the peats studied had not more than one-third as much readily soluble manganese per acre as mineral soils. One peat, on which applications of manganese gave no increase in yield, contained more manganese than other peats from the same tract on which onions and potatoes responded to manganese. These results suggest that manganese-deficient soils may be identified by means of chemical soil analysis.