2023 Volume 15 Issue 2 Pages 51-65
Because of the low organic soybean yield in Japan, we investigated the technical factors affecting the organic soybean cultivation system in 11 associations of organic soybean growers in the Tohoku, Kanto, and Hokuriku regions. Three associations (A, B and C) showed possible mineral deficiency-related physiological problems in soybeans.
The veins of the leaves in the fields of the A and B associations showed interveinal chlorosis, while the leaves stayed green. In contrast, leaves showed yellowing on the edge of the blade and curving inward or outward in the field of the C association. This study aimed to identify the physiological disorders observed and clarify the factors that induced symptoms. Plant analyses of normal and disordered blades and soil tests around the bases of normal and disordered plants were conducted.
In the field of the A association, the manganese concentration of the blade and exchangeable manganese in the soil (Ex-Mn) were lower in disorder plants that exhibited the deficient level. Soil pH was over 7. The more severe the disorder, the lower the concentration of manganese in the blade. Based on the normal visual appearance of symptoms and these results, we concluded that manganese insufficiency is the cause of this physiological disorder. Sulfur or sulfur+manganese fertilizer application decreased soil pH while increasing manganese concentrations in grass blades and Ex-Mn concentrations in soil. Thus, the symptoms disappeared and soybean yield increased with these applications. These findings support the hypothesis that the physiological problem was caused by a manganese deficiency induced by the increased pH of the soil. Only sulfur application is probably enough to prevent these symptoms. The insolubilization of manganese due to high soil pH induced by long-term excessive application of chicken and rice hull manure, whose pH was 8.5, is deemed the main cause of manganese deficiency.
In the fields of the B association, judging from the typical visual appearance of symptoms and low concentration of manganese in the blade and Ex-Mn, which showed deficiency levels, we have concluded that this disorder is diagnosed with manganese deficiency. Manganese insufficiency seems to be caused by an inadequate quantity of manganese supplied to the soil via organic fertilizer, which has more readily leaching properties.
In the fields of the C association, judging from the typical visual appearance of symptoms and low concentration of potassium in the blade and the exchangeable potassium (Ex-K2O) concentrations in the soil, which showed deficiency levels, we have determined that this disorder is diagnosed with potassium deficiency. Low soil Ex-K2O concentrations and lack of potassium fertilization may have contributed to the potassium deficiency.
