1968 Volume 37 Issue 1 Pages 51-56
Satsuma orange trees which would be induced abnormal defoliation showed two different types of characteristic spots on the leaves during fall to winter. One is light brown small spot and another is reddish brown spot. These affected leaves were abscissed from winter to spring. It was also found that the roots of these trees were falling into decay.
The leaves of the affected tree were containing much manganese, in almost all cases, having high level of more than 100ppm of manganese in dry matter basis. Soil pH was low and water soluble manganese content was high. It may be said that the remarkable increase of water soluble manganese in the soil is related to the decrease of soil pH.
Furthermore, manganese contents in the leaves may be related to water soluble manganese in the soil. In our observations, when water soluble man ganese in the soil was over 10ppm, manganese content in leaves was over 100ppm.
From the viewpoint of mentioned avove, it seemed that the“Abnormal defoliation”would be induced by manganese toxicity.
One of the main causes of it may be the increase of soluble soil manganese which due to the increase of soil acidity.
And, the increase of soil acidity may be caused by heavy application of fertilizers and insufficient application of liming materials.