Indigenous natural enemies of Orius sauteri and Orius strigicollis can suppress the population density of Thrips palmi which is the most severe insect pest on eggplants. When eggplant fields are surrounded by sorghums for windbreak, these windbreak sorghums protect the eggplants from being damaged by the thrips flying from outside the fields. Moreover, the sorghums are useful as insectary plants for indigenous natural enemies against major insect pest Aphis gossypii on eggplant. This IPM program for eggplants cultivated in open fields was named ‘Roji Nasu Shoheki Saibai: Cultivation system of eggplants in open fields surrounded by windbreak sorghum’, and this cultivation method has been in practical use for about 20 years ago. Management of the surrounding vegetation is an important technology to enhance the activity of the natural enemies. Therefore, we studied on cultivation characteristics of many horticultural wildflower species and selected some candidate species for insectary plants. About ten years ago, an IPM program for greenhouse eggplant in Okayama Prefecture was proposed based on the results of our studies, and the successful IPM program of greenhouse eggplant in Kochi Prefecture using indigenous natural enemy Nesidiocoris tenuis with its insectary plants. Recently, this IPM program has been implemented for all greenhouse eggplants in our prefecture. Through these IPM programs, the amount of chemical pesticides used in both open field and greenhouse eggplant cultivations has been greatly reduced.

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.

The use of floating plants with shading effect as living mulch for weed control in organic paddy rice farming was considered, and a comparative study was conducted focusing on Spirodela polyrhiza and Lemna aoukikusa. The shading rate of Spirodela polyrhiza is higher than that of Lemna aoukikusa. It was found that Spirodela polyrhiza has a higher light shading rate than Lemna aoukikusa, and more effectively shaded a specific wavelength range that promotes weed germination. This result suggests that Spirodela polyrhiza is a more effective floating plant for weed control than Lemna aoukikusa. The weed control effect of the mulch was verified by pot tests, and it was confirmed that the mulch suppressed the germination and growth of weeds, including the weed, Monochoria vaginalis which is considered to be difficult to control. The results of the rice field trials showed that the mulch suppressed the increase in daily maximum water temperature, which resulted in lower average water temperature until the panicle formation stage of rice plants, but had no effect on daily minimum water temperature, floodwater of dissolved oxygen concentration, pH, electrical conductivity, and redox potential. The weed control effect of the duckweed mulching was confirmed in the field, suppressing weeds, including Monochoria vaginalis, and the nitrogen produced by the decomposition of duckweed mulching increased the inorganic nitrogen concentration in the surface soil. The nitrogen produced by the decomposition of the duckweed mulching increased the concentration of inorganic nitrogen in the surface soil, which may have contributed to the growth and yield improvement of rice plants. These results suggest that organic farming of paddy rice using living mulch with duckweed may be an effective technology because it suppresses weed germination and provides nitrogen to rice plants, which may contribute to the growth and yield improvement of paddy rice.