In our previous experiment, it was strongly suggested that the main contributing factor for induction of Magoyakesyo (a physiological disorder occurring in greenhouse cucumbers cultivated by the pinching technique in Miyazaki Prefecture) is a result of high zinc absorption. Its symptom is known as a suppression of new shoots. However, it was assumed to be a complex action with copper and/or spreading agent rather than zinc only. Therefore, the interactions among zinc, copper and spreading agent on Magoyakesho were investigated. Cucumber seedlings 23 days old after grafting were hydroponically cultured under various concentrations and combinations of zinc, copper and spreading agent. Zinc was added as zinc sulfate at 3 concentrations: 0.1, 2.5 and 20mg L^<-1>. Copper was sprayed on leaves as Bordeaux mixture or copper sulfate solution at 2 concentrations: 0 and 500mg L^<-1>. The usual and latest spreading agents were used when agrochemicals were being sprayed. The results showed that zinc concentrations in leaves and tips of new shoots distinctly increased proportionally with increasing zinc concentration in the hydroponic solution. Elongation of the main and lateral new shoots was considerably suppressed in high zinc concentration treatments and was more pronounced in treatments where the latest spreading agent was used. The influence of both copper agents such as Bordeaux mixture and copper sulfate solution on the elongation of lateral shoots could not be clearly distinguished.

View full abstract

This study was conducted to evaluate the effect of flooding in the latter growth stage (from the 15th day before heading to the 25th day after heading) on cadmium (Cd) uptake by lowland rice (Oryza sativa L. cv. Koshihikari) in a slightly polluted paddy field with Cd in the Jinzu River basin where the Cd content in brown rice was around 0.4mg kg^<-1>. With flooding in the latter growth stage Cd content in brown rice was 0.08mg kg^<-1> and as compared with a control plot managed by intermittent irrigation after midsummer drainage, percent of reduced Cd content was 84%. In addition, the probability that Cd content in brown rice would exceed 0.2mg kg^<-> was under 2%, taking annual change into consideration. With flooding in the latter growth stage Cd uptake by rice plants from the 15th day before heading to harvest time was reduced to 10% equivalency of the control plot. Considering changes of soil oxidation-reduction potential and pH, it was suggested that Cd in soil existed in insoluble form as sulfide in the flooding period. As to rice yield a clear influence from flooding was not found. Roots of the rice plants on the 20th day after heading were not injured under reductive soil conditions. Though trafficability of harvester on topsoil was degraded by flooding with a decrease of bulk density and hardness of surface soil, physical properties of the topsoil were improved by restricting the flooding period within the latter growth stage as compared with continued flooding from transplanting to the 25th day after heading. In conclusion, water management based on flooding for 40 days in the latter growth stage from the 15th day before heading to the 25th day after heading is efficient to decrease Cd content in brown rice as low as is reasonably achievable.

View full abstract

The effects of use of the phosphorus medium (P-medium) as nursery bed soil on the growth and nutrient uptake of rice seedlings (Oryza sativa cv. Hitomebore) were examined. The ratio of shoot dry weight to shoot length of rice seedlings was improved when treated with P-medium. Nitrogen, phosphorus and potassium contents of rice seedlings in the P-medium treatment plot were the same as those in the control plot. On the other hand, silicon content was increased with P-medium. The effects of co-situs application of the P-medium on the growth and phosphorus uptake of rice plants were also examined in pot experiments. Two types of soil were used in this experiment, subsoil from a Zao and subsurface soil from a Mouka paddy field. The dry weight, amount of phosphorus uptake and phosphorus recovery rate of rice plants with P-medium treatment were the same or more than those in the triple superphosphate treatment plots (side-dressing and broad casting) in both soil types. Rice plants were grown again without phosphorus application in the Zao soil after harvest of the first cultivation. The dry weight and amount of phosphorus uptake were highest in the P-medium treatment plot. The cumulative recovery rate of phosphorus fertilizer was also highest in the P-medium treatment plot (about 60%).

View full abstract

Large variations in the breaking stress of tofu from soybeans (var. Toyomusume) occurred in a region of central Hokkaido where soybeans were produced instead of paddy rice. The breaking stress of tofu had a significant positive correlation (r=0.85, p<0.01) with seed protein contents, but none with phytate or calcium contents. In fields where soybeans were cultivated after paddy rice for the first time, scarcely any nodules were formed on the soybean roots due to low soil Rhizobium concentration. Some of such soybean plants tended to have low leaf color values (measured by a SPAD chlorophyll meter) at the late flowering stage and also low seed protein contents at harvest. By contrast, a large number of nodules were found on their roots, the chlorophyll content of leaves was high, and then seed protein content was also high in fields where soybeans had been cultivated after paddy rice. We concluded that soybean cultivation history after paddy rice production was crucial in determining soybean seed protein contents and also textural properties of tofu in a paddy rice region of central Hokkaido.

View full abstract

Quantitative methods for analyzing about 9 kinds of isoflavones using HPLC were established for soybean seed. First, 8 kinds of isoflavones (daidzein, glycitein, daidzin, glycitin, genistin, malonyldaidzin, malonylglycitin and malonylgenistin) except for acetylglucoside and genistein were purified from hypocotyls of soybean to make standard material for the analysis. Because malonylglucosides among the purified isoflavones decomposed easily, malonyldaidzin, malonylglycitin and malonylgenistin were used only for the confirmation of these retention times. Using the change in glucoside to be decomposed from malonylglucoside as substrate, the solution of purified malonylglucoside fraction was analyzed by HPLC before and after being left for 10 weeks at room temperature in a dark place. The mass area ratio of each malonylglucoside based on the area of 1mg L^<-1> of daidzin on the chromatograph was calculated from both that peak area decreased in the 10-week period and the peak area and concentration of glucoside increased in that same period. It was guessed that a period of at least about five weeks would be necessary to calculate a mass area ratio in a similar experiment. The method was established to quantify each malonylglucosides from the mass area ratio and the ratio of the area of standard material daidzin against the area of malonyldaidzin, malonylglycitin and malonylgenistin on chromatographs.

View full abstract

A low fertilizer application technique was studied for summer welsh onion by applying a release-controlled fertilizer to substrate in chain pots. 1. The nitrogen release rate of a coated ammonium nitrate phosphate (2401-100S) of a 100-day sigmoid type for suppressed initial nitrogen release was 3.3% during the period of raising seedlings. No high-concentration damage was observed on welsh onion nursery plants, which grew as well as standard cultivation nursery plants. 2. Under a constant amount of top dressed nitrogen (standard application rate of nitrogen, 160kg ha^<-1>), the amount of nitrogen from 60kg ha^<-1> of the 100-day type coated ammonium nitrate phosphate by the application method in the chain pot system yielded an equivalent harvest to that from a standard application rate (basal dressing nitrogen, 80kg ha^<-1>). From the nitrogen release rate of this fertilizer, top dressing applied three times was judged adequate in contrast to four applications prescribed for the standard application rate. 3. When 60kg ha^<-1> of the 100-day type coated ammonium nitrate phosphate was applied in the chain pots, 90kg ha^<-1> of top dressed nitrogen resulted in an equivalent harvest to that from the standard application rate. The total amount of applied nitrogen was 150kg ha^<-1>, which was 38% lower than 240kg ha^<-1> from the standard application rate of nitrogen. The utilization ratio of applied nitrogen also increased to 43% in contrast to 25% for the standard application rate. 4. Soil nitrate in the soil after cultivation from the application method in the chain pot system was lower in all soil horizons ranging 0-60cm than that from the standard application rate.

View full abstract