| OCR Text |
Show A Manganese Nutrition Problem 43 The only tions on leaves and soil are summarized in Table 4. consistent result of the leaf analysis data was that the diseased leaves were considerably lower in manganese than the normal leaves. Soil from near the diseased trees was slightly lower in exchangeable manganese than that from near normal trees, but there was no consistent difference in the amount of manganese reduced in the soils by hydroquinone. DISCUSSION Data obtained on the disease investigated indicate that it is caused by a deficiency of available manganese in the soil and that the disease can be controlled by injecting manganese salts into the two pounds of manganese sulfate to the soil trees or by adding about each tree. The evidence supporting the conclusion that the disease is the result of a manganese deficiency can be summarized as fol lows: (1) Disease symptoms disappeared upon injecting the trees with manganese sulfate or after adding manganese sulfate to the soil. (2) The disease was not controlled by treatment with any of a number of essential nutrient elements other than manganese. (3) Leaves from diseased trees contained much less manganese than leaves from nearby normal trees. (4) The severity of the disease symptoms was generally increased by tree injection with soluble iron phosphate. The nature of the evidence in the fourth point depends upon the intimate relationships between iron and manganese in plant nutrition. Both elements are apparently absorbed and are active in plants in the reduced, bivalent forms. High manganese in plants results in the iron being oxidized to the relatively inactive ferric form so that the resulting leaf chlorosis can be termed either iron deficiency or manganese toxicity. Conversely, if manganese is low and iron is plentiful an excess of iron becomes active in plant tissues and the resulting leaf disease symptoms can be termed either manganese deficiency or iron toxicity. These relationships between iron and manganese have been shown in a number of publications, but especially in the report by Somers and Shive". Since in the present investigations injection of affected trees with iron tended to increase the disease symptoms, additional evidence is obtained that the manganese supply in the plants is very low. In terms of the possible distribution of the manganese de ficiency disease, the soil characteristics are of interest. The soil in the east part of Bountiful where this occurrence of the disease was studied is a non-calcareous coarse sandy loam formed principally |
