Results of further investigation on Satsuma orange orchards which were suffering from the“Abnormal defoliation”

Abstract

In 1961, the authors have made investigations on a number of Satsuma orange orchards which were attacked by the so-called“Abnormal defoliation.” And the present study was carried out in 1966 with some of those orchards examined formerly to make clear the recent situation of the orchards which have hitherto experienced certain recovery measures for such disorder.1. Since 1964, those orchards attacked by“Abnormal defoliation”became getting somewhat better in condition, revealing that the occurrences of defoliation, brown spots on leaves and of decay of fibrous fine roots were remarkably infrequent2. In the orchards which were still suffering “Abnormal defoliation”it was observed that both the manganese content in leaves and the soil acidity showed definite decline as compared with the results of former survey, although those soils showed always much higher levels of manganese content and of acidity than those of the intact healthy orchard soils.3. In the orchards examined there could be noticed that the decreasing supply of nitrogen, and, in turn, the increasing use of lime, revealing that such practical measures might be duly appreciated to be somewhat effective for recovering from this disorder.4. Negative correlation was obtained between the content of water soluble manganese and pH level in the soil. The more higher correlation was met with the more higher level of easily reducible manganese in the soil5. In the former survey in 1961, a close relationship was obtained among the“Abnormal defoliation, ” manganese content in leaves, soil acidity and the water soluble manganese content in the soil. But, on the contrary, the result of present examination could not reveal clearly so much closer relationship as above stated. Therefore, it may be suggested that the period of surveying would have a no less important bearing on the result obtained.