The causes and prevention of the leaf dying symptom of the melon was investigated which had broken out in the calcareous soils of Kikaijima Island, Kagoshima Prefecture. The results obtained are summarized as follows : 1) The competitive inhibition of magnesium absorption by the excess absorption of calcium, which was characteristic in the calcareous soils, was considered to be the cause of the leaf dying symptom. 2) The leaf dying symptom was prevented through the foliar spraying of magnesium solution at the beginning of the outbreak. 3) The leaf dying symptom was also prevented through the application of MgSO_4 which decreased the Ca/Mg ratio of the soils to 6. 4) The excess application of potassium increased the leaf dying symptom. We consider that this was because potassium in the soil enhanced the competitive inhibition of magnesium absorption by calcium.

View full abstract

Seasonal changes of water-insoluble, soluble and gaseous F concentrations of aerosols in day and night times from June, 1988 to April, 1989 in a non-industrial area, were investigated in Morioka, Northeast Japan. The water-insoluble and soluble F concentrations were higher from November to April than from June to October. On the contrary, the gaseous F concentration was high in summer, probably because of influences of the steel industrial area in the Pacific coast region and wind-blown sea salt from the Pacific Ocean. The water-soluble F concentration of aerosols from Changchun, Northeast China in March and July to December, 1991,which are mainly due to coal soot, was extremely high in the winter season and was 116 times higher than that from Morioka. In addition, Holocene, Malan and Lishi Loesses, loess-derived soils, and saline soils from Xinjian Uygur Zizhiqu, the Loess Plateau, and Northeast China, where there is a high incidence of endemic fluorosis, contained a considerable amount of water-soluble F. However, the amount of water-soluble F in loess-derived soils from Korea and Japan was very low, indicating that F was leached out by heavy rainfall. The aerosols collected at Morioka from winter to spring contained a significant amount of coal soot and eolian dust. The F concentration of aerosols in Japan, therefore, could be influenced by coal soot and eolian dust transported from the Asian continent. These airborne particles could affect the water-insoluble and soluble F concentrations of aerosols in Japan.

View full abstract

Yacon (Polymnia sonchifolia), a perennial plant of the family Compositae, accumulates a large amount of fructans with relatively low DP in the tubers and tuberous roots. We investigated the seasonal growth and fluctuations of the water soluble carbohydrate content in each part of the yacon during the growth and dormancy periods. The most vigorous growth of the aerial parts and tuberous roots was observed in September. The tubers swelled rapidly in November. Thereafter the leaves and stems completely died due to the frost in the middle of December. Fructans were the predominant water-soluble carbohydrate in the tubers and tuberous roots throughout the growth period. The amount of fructans in the tubers increased rapidly in November and remained constant during the dormancy. While the amount of fructans in the tuberous roots increased dramatically in September, there was a significant decrease in fructan content during the period between October and March.

View full abstract

Spinach and komatsuna were cultivated with 0,10,15 and 30g N m^<-2> applications in an Ando soil, and the changes of the contents of sugars, ascorbic acid, nitrate and oxalic acid which are the constituents related with the quality of the vegetables, and the relations between the growth (fresh weight), nitrogen status and the contents of these constituents were investigated. Ascorbic acid is contained both in spinach and komatsuna, but oxalic acid is contained at a high level in spinach and at trace levels in komatsuna. Nitrate nitrogen contents increased along with the increase of applied nitrogen, and reached 1.14g (kg FW)^<-1> in spinach leaf petiole and 1.26g (kg FW)^<-1> in komatsuna leaf petiole at harvest with the application of 30g N m^<-2>. In both crops, sucrose content was highest in the plot of 0g N m^<-2>, glucose content was highest in the plot of 10g N m^<-2>, and they were lowered with increased application of nitrogen. Total ascorbic acid (ASA+DHA) content was decreased by increasing the nitrogen application : from 0.74g (kg FW)^<-1> at the plot of 0g N m^<-2> to 0.51g (kg FW)^<-1> at the plot of 30g N m^<-2> in spinach and from 1.00g (kg FW)^<-1> at the plot of 0g N m^<-2> to 0.48g (kg FW)^<-1> at the plot of 30g N m^<-2> in komatsuna. In spinach, the total (water-soluble plus-insoluble) oxalic acid content was increased in the leaf blades and decreased in the leaf petioles along with the increase of nitrogen application, and there was no difference in the whole leaves with the treatments. The contents of sucrose and ascorbic acid were high in the plants in which yield and nitrogen content were low and dry matter content was high. In view of the quality of spinach and komatsuna, the low nitrogen application is better, but the amount of nitrogen application must be determined considering the maintenance of growth and yield.

View full abstract

Coating resin chemical fertilizer using alkyd resin and polyethylene resin is added into soils, and it is a problem that these resins remain in the soils. Therefore, we investigated the degradation of these resins in the soils. The results obtained were as follows. 1) The dergradation ratio of alkyd resin was higher than polyethylene resin. Three month later, the former was 4.5% and the latter was below 0.5%. The result that the degradation ratio of alkyd resin was higher in soil with a high humus content suggested that the degradation of the coating material is microbiological. 2) There were no differences between alkyd and polyethylene resins in the number of microorganisms on the coating membrane surface and in the soil around the coating membrane, but the number of fungi in the former was about 100 times higher in the coating membrane and was about 10 times higher in the soil around the coating membrane than in the latter. In addition, using the trial box for the measurement of enzymatic activity, soil enzymatic activity concerned with the degradation of alkyd resin membrane was measured, and the results showed that the activity of the soil enzymes was high nearer the membrane. 3) Under field conditions, we took the buried membrane out of soils and observed its surface by electron microscopy. It was observed that the surface of the alkyd resin membrane was consequently degraded than the surface of polyethylene resin. These results definitely show that the alkyd resin membrane was degraded faster than the polyethylene resin membrane by the microorganisms in soils, and it thus appears to be a good material for use in coated fertilizer.

View full abstract

It is thought that using slow-release fertilizer is one way of reducing groundwater pollution from intensive fertilizer application. We confirmed the effective use of coating fertilizer, which is one of the slow-release fertilizers, in two experiments. The first experiment was eluviation under controlled conditions, and the second was a pot experiment using cucumbers with coating fertilizer marked with heavy nitrogen. The results are summarized as follows. 1. Experimental eluviation 1) Eluviation quantity from readily available fertilizer is greater than from coating fertilizer. 2) Nitrogen quantity in soil of coating fertilizer is greater than of readily available fertilizer. 2. Pot experiment using cucumbers 1) Eluviation quantity from readily available fertilizer is greater than from coating fertilizer. This result is the same as the experimental eluviation. 2) Nitrogen recovery rate to plants for each period is higher in coating fertilizer than readily available fertilizer. 3) In upper soil, the residual quantity of applied nitrogen-fertilizer decreased quickly over time with readily available fertilizer, but it remained at high levels with coating fertilizer.

View full abstract

We investigated the effects of nitrogen on rice plant height, the number of tillers and ears, culm length and number of grains of different gibberellin levels following treatment with gibberellin (GA_3) and a gibberellin biosynthesis inhibitor (uniconazole-P). Nitrogen made the characteristics increase. GA_3 increased plant height, culm length and number of grains per ear and decreased other characteristics. GA_3 and uniconazole-P had the opposite effects. These results suggested that the increasing effect of nitrogen on plant height and number of grains per ear was connected with the increasing gibberellin level, however the effect of nitrogen on the number of tillers and ears was not caused by gibberellin, because the number of tillers and ears increased under the low gibberellin level by uniconazole-P treatment.

View full abstract