A field experiment was conducted to study the effect of spacing (20×10cm, 25×15cm and 30×20cm) and nitrogen level (0, 40, 60, 80 and 100kg/ha) on weed infestation in transplanted rice. Transplanted rice was weeded twice—25 and 45 days after transplanting. Before each weeding, observations on weeds were made. Weed species growing in the experimental plots were identified, their number counted species-wise together with rice hills, and the relative density of each species at various spacings and nitrogen levels was analyzed. Results clearly revealed that the relative weed density of each species increased with the increase of the spacing or nitrogen level in transplanted rice. Weed densities were prominent particularly in rice grown at wider spacings, but decreased gradually with the increase of the rice population or decrease of spacing. The effect of the nitrogen level on each of the infesting nine weed species was investigated and attempts were made to quantify the effect using a linear regression model of the form y=mx+c. All the species showed a linear relationship and different behavior with the applied nitrogen. Equations obtained with a high r² value (ranging from 0.818-0.973) for each of the species were different from each other, reflecting the variations in the increasing rates of relative weed densities. With the increase in every kg of N/ha, increasing rate of Cyperus iria was highest (0.015% at W₁ and 0.017% at W₂) among the nine infesting species followed by Paspalum distichum and Scirpus mucronatus. Relative density of weed vegetation of each species associated with the nitrogen level in transplanted rice can be predicted using the equations obtained from the study. However, these results may vary in different agro-environmental areas.

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Sugar-containing sap obtained from Indonesian palm trees by traditional methods and brown sugar produced from it were analyzed for general, sugar and organic acid compositions. Fresh sap collected from sugar palm (Arenga pinnata Merr.; aren/enau in Indonesian), palmyra palm (Borassus flabellifer L.; siwalan/lontar), nipa palm (Nypa fruticans Wurmb.; nipah), and coconut palm (Cocos nucifera L.; kelapa) contained 10 to 13% of sugars which consisted mainly of sucrose. When fresh sap from sugar, palmyra and nipa palms was incubated, significant amounts of glucose and fructose and some amounts of oligosaccharides were generated by the action of microorganisms. The sap from palmyra, nipa and coconut palms contained succinic acid as a dominant organic acid while sugar palm contained malic acid. Incubation of the fresh sap from sugar and nipa palms for one day resulted in the increase in the content of lactic acid. The ratio of reducing sugar to total sugar in fresh sugar palm sap increased remarkably from 12.5 to 90.1% by incubation at 30°C for 16 hrs. Higher ratios ranging from 36.1 to 43.0% were recorded for brown sugar from sugar, palmyra and coconut palms.

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In a pot experiment with Ando Soil, the effect of compaction on three phase distribution of soil, and soybean (Glycine max L. cv. Suzuyutaka) growth at early blossom stage was studied in control conditions. Soil compaction significantly decreased total porosity, void ratio and air phase. On the other hand, degree of saturation, bulk density, and solid and liquid phases increased with increased levels of compaction. Soil compaction also significantly reduced the root weight, root volume, maximum root length, root density and root shoot ratio. However, the degree of soil compaction did not have a statistically significant effect on plant height, stem and petioles weight, and leaf weight of soybean after 42 days of growth. In this study it was observed that root development was affected by the levels of soil compaction but were not the plant shoot parameters.

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The rat's tail radish (Raphanus sativus) Pakki-hood is cultivated in northern Thailand. Pakki-hood produces inflorescences and a large number of young siliquas which are used as a vegetable. The response of Pakki-hood to low temperature was examined in order to determine its suitability for winter sowing cultivation in Japan. Though the germination rate decreased with the decrease of the temperature, a significant difference was found in the germination at 5°C between Pakki-hood and Japanese cultivars. Only Pakki-hood was able to germinate at this temperature. The critical temperature for the growth of Pakki-hood seedlings ranged from 5 to 10°C. The hypocotyls of Pakki-hood and ‘Shogoin’ grew spindly at above 15 and 20°C, respectively. When seedlings grown at a higher temperature (25/20°C) for 5 days were chilled for 3 days or more and returned to the 25/20°C regime, the hypocotyl growth of Pakki-hood was markedly inhibited. Seedlings showed distinct symptoms of chilling injury after 3 days of chilling treatment. Electrolyte leakage from chilled hypocotyl grown at higher temperature increased remarkably. It was shown that the cells of the hypocotyl were disrupted by chilling at 0°C for more than 2 days. As the rate of inhibition of photosynthesis of Pakki-hood at low temperatures was much lower than that of the other Japanese radish cultivars, Pakki-hood photosynthesis is considered to be resistant to low temperature.

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Rice (Oryza sativa L.) yield was considered to depend on dehydration tolerance in drought-prone lowland environments. This study was designed to analyze the relationship between dehydration tolerance and absolute and relative yield under drought conditions across genotypes. Ten and twenty-four genotypes differing in ecological adaptation in 1987 and 1988, respectively, were grown under two rain shelters. In one shelter plants were subjected to submerged conditions as control and in the other to drought conditions initiated at the booting stage in early genotypes and terminated by flooding the soil at the heading stage in late genotypes. Dehydration avoidance was determined based on cumulative water stress (integrated water stress with time) and dehydration tolerance was determined based on water stress susceptibility (fractional decrease of yield per unit change of cumulative water stress) . Although there was no relationship between dehydration avoidance and the plant developmental stages, dehydration tolerance and relative yield changed with the plant developmental stage when the plants were subjected to water stress. Generally, both tolerance and relative yield were lower in genotypes subjected to water stress at the early stage of grain filling than in those subjected to water stress at the late stage of grain filling. However, Guizhao2, IR36 and Milyang23 were dehydration-tolerant and produced higher relative yield among such genotypes when subjected to water stress at the early stage of grain filling. Since Guizhao2 produced the highest yield under the control conditions, it also produced the highest yield under drought conditions. These results suggest that dehydration tolerance can be improved for the breeding of drought-resistant rice varieties.

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The storage conditions under which mechanically injured sweet potato tuberous roots produce and accumulate ipomeamarone (Ip), a typical phytoalexin, were examined.
Sweet potato tuberous roots were injured by scratching over half of their sides under sterilized conditions and were kept under high humidity (“Wet”: RH 85-95%, 13°C or 25°C) or low humidity (“Dry”: RH 60-70%, 13°C or 25°C) conditions for 3, 7, 14 and 21 days, and then they were divided into two portions, injured and non injured sides for chemical and physical analyses.
Under high humidity conditions, no remarkable changes including darkening were observed in either portion and Ip was not detected.
In contrast, under low humidity conditions, weight loss, decrease in starch value, increase in the content of polyphenols (PP), etc. were clearly observed and the alterations were more severe on the injured side. Induction of Ip occurred on the injured side. The deterioration along with the induction of Ip was markedly promoted at 25°C.
Among the cultivars used in this experiment, i. e. Koganesengan, Shiroyutaka and Kokei-14, the former two were more susceptible to injury by scratching.
The intact sweet potato tuberous roots kept under low humidity conditions did not lose weight appreciably, and no Ip was detected.
These facts indicate that Ip induction in mechanically injured sweet potato tuberous roots was caused by subsequent storage under low humidity conditions. It is generally recognized that “wound healing” of cell layers beneath the wound surface is considerably slow and incomplete under unfavorable conditions such as low humidity. Accordingly, it is suggested that, under low humidity conditions, injury by scratching cannot be healed and continuously acts as a stress for the induction of Ip.

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