1. The experiments reported here are the summary of the results carried out to clarify seed behaviour in the field in relation to emergence of three representative weeds in Hokkaido.
2. Results of the field experiment showed that the seed dormancy of Chenopodium album and Echinochloa crus-galli var. praticola was broken more rapidily in the soil layer than on the soil surface, in the period from early November to early December before soil freezing occurred (Table 1.). The seeds which had lost the dormancy were supposedly remained in the field in the state of the enforced dormancy until soil temperature rises.
3. Percent germination of seeds which had lost the dormancy was considerably influenced by the temperature conditions in the dark (Fig. 2). In C. album, the germination rate was very low at any constant temperature, but it increased remarkably when 5°C was combined with higher temperature in the alternating temperature treatment: that of 5°/30°C gave the highest germination. In E. c. var. praticola, very low germination rate at constant temperature of 5°-20°C was increased by the combination with 25° and 30°C, and the increase was greater when lower temperature was combined with higher temperature, showing 100% germination at 5°/30°C. In P. lapathifolium, the reaction of seeds to temperature was similar to C. album at 15° and 20°C, and to E. c. var. praticola at 25° and 30°C respectively.
Pre-irradiated seeds showed a great increase in germination over the wide range of the temperature conditions examined (Fig. 2).
4. Some possible involvement of light in germination, after the seed dormancy was broken, was experimentally acertained. Most of seeds were stimulated in their germination when an ambient temperature was maintained at 20°C. The most effective wave length of light was 660-690nm for germination of C. album and E. c. var. praticola, while only weak stimulation by 490-660nm was found in P. lapathifolium seeds. And a brief irradiation such as 400μW at 660nm for 2 seconds was sufficient to elicit germination about 50% of the seeds, and that for 60 seconds was over 70% (Fig. 4).
5. It was demonstrated that the seasonal emergence patterns of these weeds during the time from spring to summer are controlled mainly by the diurnal soil temperature variation in the soil surface layer (Fig. 3). However, an apparent discrepancy between the actual pattern of emergence and the estimated curve of germination was recognized with P. lapathifolium from June onward, and with C. album in October. It was proved to be caused by the secondary dormancy occurring during the period from summer to autumn.
6. It seemed that the ungerminated seeds were in the state of thermodormancy; namely, they re-entered into a dormant state due to high temperature in the summer and the dormancy was terminated by the end of November as the temperature lowered. The seeds buried in shallow soil layer were exposed to the secondary dormancy faster than the deeply buried seeds (Table 2).
7. The population of seeds buried in the soil decreased exponentially, and the decreasing tendency of population in the disturbed soil was more noticeble as compared with seeds buried in the undisturbed soil.

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Biological activities of leachates from dried and decayed materials of several herbs were tested to survey the physiological effects of grass mulch in orchards. Peach seedlings were grown in the mixture of soil and cut foliage of Artemisia princeps, Rumex japonicus, Polygonum longisetum, Cyperus rotundus, Digitaria sanguinalis, Trifolium repens or Lolium multiflorum: Growth ratio of shoot/root increased in all the mixture treatments, though it varied depending on the treated species, showing lowest ratio in P. longisetum.
Aqueous extracts of ground foliage of D. sanguinalis, A. princeps, P. longisetum, R. japonicus, T. repens and Amaranthus viridis, and extract of ground rice-straw were assayed for their activities using lettuce: Promotion in shoot elongation and inhibition in root elongation were observed, though the rate varied with the concentration, in most of the extracts except for P. longisetum and rice-straw. P. longisetum decreased both shoot and root length of lettuce plants, whereas the rice-straw increased them. These original activities changed as the degradation in soil proceeded, exhibiting similar fluctuation pattern in each treatment.
The above results proved to be partially related to nitrogen levels of the extracts or he leachates, but participation of other factors was also suggested.

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This study showed that the growth in early stage of fourteen local populations of barnyardgrass (Echinochloa oryzicola Vasing) in seedlingcases had depended on different temperatures and light intensities.
Three levels of light intensity i. e. 100, 40, and 25% were provided by shading treatments during each of two seasons, when average air temperature was 33.3 or 24.3°C for the 23-day growth period.
Results of this study are summarized as follows;
1) Crop growth rate (CGR), leaf area (LA) and net assimilation rate (NAR) increased as light intensity approached the level of full sunshine, and under the same light intensity these parameters increased at the higher air temperature.
2) The differences among fourteen populations tested were recognized to be greater in CGR and LA than in NAR. Much higher significant correlation coefficient was obtained between CGR and LA than between CGR and NAR.
3) From data on individual variation within populations expressed by the coefficint of variance on plant height and number of leaves, the degrees of variation decreased as light intensity approached full sunshine, and these degrees, on the contrary, showed a tendency to increase under the lower light intensity.
4) The degrees of phenotypic plasticity expressed by the coefficient of variance of CGR, LA and NAR which were obtained under the six different environments decreased in the order of CGR, NAR and LA, and differences between populations were also revealed on these characters.
5) Significant negative correlation was attained between the degrees of phenotypic plasticity and the individual variations within populations tested in this trial.
According to these results, it is presumed that the complemental effects of the above two characters act mutually to the change of environment.

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Changes of Weed emergence and their growth were studied by applying a series of calcium carbonate dosages at an immature upland field. The weed species studied were Zoysia japonica Steud., Arthraxon hispidus Makino, Houttuynia cordata Thunb., Cassia minosoides L., Rumex Acetocella L., and Achyranthes japonica Nakai. All of these species were planted at the first year and then after only annuals were sowed in early December of the consecutive three years. During the period of four years, there were little trends of the changes in soil physical properties such as the hardness and percent aggregate between weed vegetation, amount of the carbonate applied and the order of year. Excluding in the first year, the six species of weeds emerging decreased in fresh weight as the soil pH decreased and the year progressed. Some of the experimental plots with high calcium carbonate dosages showed no or little emergence of the weeds in the third or fourth year. Lethal soil pH (KCl) was estimated at 5.40 for Zoysia japonica Steud., 5.60 for Arthraxon hispidus Makino, 5.65 for Houttuynia cordata Thunb., 5.25 for Rumex acetocella L. and 5.67 for Achyranthes japonica Nakai. The pH values for the above respective weeds had been 4.72, 5.33, 5.08, 5.25 and 5.25 according to the previous investigations. Thus, the pH ranges observed both by the present and previous investigations appear to be theindexes for an ecological control of these weeds by a soil pH aletrnation. Though a soil acidity changes a little depending upon enviromental conditions, the determination of lethal soil pH range for weeds is beneficial to establish an ecological control measure for the particular weeds in the processes of field maturation.

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The emergence of sprangletop, Leptochloa chinensis Nees was investigated under five levels of soil moisure and five times of soil cultivation.
1. Emerged number of the weed was little different from upland field condition to 10cm level of groundwater, but it decreased under the water-saturated condition by half.
2. The duration of emergence differed from time to time of soil cultivation. It was about 50 days in late May, about 30 days in the middle of June, and about 20 days in July-August. This change may be concerned with the dormancy of seeds.
3. The Weed scarcely emerged in the early autumn. This fact may be concerned with the secondary dormancy of seeds.

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In order to clearify the mechanism of phytotoxicity against rice plants caused by soil treatment of simetryne, the effects of several enviromental conditions, especially the air humidity, to the phytotoxic symptoms and to the content of simetryne in rice plants were investigated.
Simetryne was applied on the watersurface of submerged soil after transplanting the rice seedlings. The results are as follows.
1. Necrosis of lower leaves of main stem and of tiller leaves was the main symptom of simetryne phytotoxicity at the early stage, thereafter these symptoms were observed in upper leaves. Dry weights and number of tillers of rice plants reduced remarkably by simetryne application. The degree of those reduction showed good relation with the applied dose of simetryne and with the saturation deficit.
2. The content of simetryne in rice plants was higher at lower humidity and in lower leaves than at higher humidity and in upper leaves. The degree of phytotoxicity was closely related with the content of simetryne in rice plants, and the maximum content of simetryne was found at one or two days after treatment.
3. Detached leaves were dipped into dilute solution containing simetryne, and the amounts of simetryne found in the test leaves were compared with theoretical amounts translocated from solution. The ratio of these two amounts was postulated as the rate of metabolism of simetryne, which showed no difference among leaf positions of rice plants.
4. It is said that simetryne may move in rice plant along the apoplast system. The upper phytomer units of the rice plants treated with simetryne did not fully developed, and this phenomenon seems to suggest that simetryne phytotoxicity has a close relation with the development degree of phytomer units in rice plants.

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In order to investigate the seasonal change in Seed dormancy of main upland weeds, seeds of 10 species were buried in soil at 5cm depth on November 1979 and were exhumed in February, May, August and October, 1980. Germination of the seeds exhumed was tested in 30°C-20°C growth chamber.
(1) Porturaca oleracea and Amaranthus lividus showed high germination percentage just after harvesting seeds, and the other species showed high germination percentage on February and May after passing winter. Dormancy of all the species was broken considerably until Feburuary and May next year.
(2) As Digitaria adscendens, Echinochloa crus-galli var. praticola, Chenopodium album and Polygonum lapathifolium exhibited low germination percentage in summer season, it was recognized that they had secondary dormancy. Secondary dormancy was not recognized on Cyperus microiria, Porturaca oleracea, Amaranthus lividus and Fatoua villosa.
(3) Germination percentage of all the species was higher in light condition than in dark condition, and it was recognized that all the species had light requirement much or a little. Especialy, Cyperus microiria and Porturaca oleracea did not germinate at all in dark condition.

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