Growth of Sagittaria pygmaea Miq. and Cyperus serotinus Rottb., and their influences on rice were investigated in field experiments, in which each of three rice cultivars different in maturing time were transplanted at two different dates (early and normal planting). Sprouted tubers of each of the weeds were transplanted between rice rows at the density of 22.2 tubers per m².
In early planting of rice, S. pygmaea propagated most vigourously in early maturing cultivar of rice and reached to more than 1100 stands per m² by autumn. The number of formed tubers were almost proportional to the stands of S. pygmaea.
More aerial shoots of C. serotinus were emerged in early planting than in normal planting of rice, although there were not marked differences in propagation of C. serotinus between rice cultivars. Formation of tubers was influenced by harvesting time of rice.
While growth of rice infested with S. pygmaea was little affected, C. serotinus influenced seriously on LAI, dry matter production and CGR of rice since tillering stage and reduced panicle number and grain yield of rice in all plots.

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A study of weed community of sown grasslands was carried out in Hokkaido. The weeds most frequently observed were Taraxacum officinale, Rumex obtusifolius and Plantago asiatica. Local endemic weeds in Hokkaido were Taraxacum officinale, Artemisia montana and Geum aleppicum, etc.
Weed communities were classified as follows:
I. Chenopodium album-Polygonum longisetum type (Differential species; Chenopodiumn album, Stellaria neglecta and Capsella bursa-pastoris).
1. Amaranthus patulus-community (Differential species; Amaranthus patulus, Solanum photeinocarpum and Setaria faberi).
2. Poa annua-community (Differential species; Poa annua, Polygonum aviculare and P. aequale).
3. Typical community.
II. Typical type
4. Typical community
5. Hydrocotyle ramiflora-community (Differential species; Hydrocotyle ramiflora).
III. Plantago lanceolata type (Differential species: Plantago lanceolata, Oenothera biennis, Rumex acetosella, Equisetum aivtense and Geranium thunbergii)
6. Typical community
7. Hypochoeris radicata-community (Differential species; Hypochoeris radicata, Rubus parvifolius, Phragmites comnunis, Cynanchum caudatum and Spiranthes sinensis)

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Dynamics of weed communities of sown grasslands was analysed in the present report after having presented the classification of the weed community in a previous report.
Edaphic conditions and management of pastures such as fertilizing, mowing and grazing were most important factors in determining the dynamics of weed community. Chenopodium album-Polygonum longisetum type (Type I), which was found in the eutrophic site changed to Amaranthus patulus-community by heavy fertilization and as a result of the large amount of feces from grazing animals and changed to Poa annua-community as a result of overgrazing.
Typical type (Type II), observed in the mesotrophic site changed to Hydrocotyle ramiflora-community in areas with poor drainage. Plantago lanceolata type (Type III), which was observed in the oligotrophic site tended to shift to Hypochoeris radicata-community in sandy soil. Thus, it appears that weed communities can shift from one to another under the influence of changes in edaphic conditions and management.
These weed communities were also discussed in relation to P-A index and life form of composed weed species.

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Change in plant vegetation caused by the application of soilac on the newly cultivated field of fairly old volcanic ash soil was investigated.
1. Weed species that grew in the first year after the application of soilac were those of wild type. After 2 to 6 years, weeds of wild and farm types grew together. The major weed species observd were almost the same in each year in all the test plots and no significant differences were observed in weed vegetation.
2. In each year tested, no significant differences in weed population and total weight of weeds were observed in three test plots to which soilac was applied at the rate of 0, 50, and 100kg per 10a, respectively. However, weed population and total weight increased considerably at the plots of application of 200 and 400kg per 10a.
3. Anual change of the chemical properties of soil were almost the same in all the test plots. However, soil hardness were decreased and degree of aggregation were increased by the application of 200 or 400kg of soilac per 10a.
4. The threshold values at which increase of weed population and total weight occurrd were depression of 1.86-2.23kg/cm² in soil hardness, and increase of 3.18-5.54 percent for intact soil and 2.49-5.75 percent for air dried soil in content of soil particles over 0.5mm.
5. Effect of soilac to soil appeared to be maintained for about three years by the application of 200kg per 10a, and for five years by the application of 400kg per 10a, when soilac was applied evenly in the soil to the depth of 28cm.

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The efficacy of OM as an antidote for reducing the phytotoxic action of auxin type herbicides, especially, anti-curvature effect of soybean treated with chloramben was tested in a greenhouse.
(1) Fenac toxicity to wheat, rice and sawa millet was greatly diminished by the addition of OM. Similar result was recognized with butyl-2-(3, 4-dichlorophenoxy)-propionate toxicity.
(2) 1, 10-Decamethylenediamine (DM) possessed an effective antidotal activity for reducing chloramben injury (stem curvature) to soybean without top growth inhibition of soybean.
(3) OM was the most effective in promoting soybean top growth, among the α, ω-diaminoalkanes (DA) tested by foliar application.

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These studies were conducted to obtain some informations on the herbicidal properties of the two uracil derivatives, such as 5-bromo-3-n-butyl-6-methyluracil (S-113) and 5-bromo-3-iso-butyl-6-methyluracil (S-114).
(1) Both chemicals, S-113 and S-114, showed higher selectivity than bromacil for leguminous crops on pre-emergence treatment in green house. The descending order of the selectivity of S-113 among them was shown as pea=azuki bean>soy bean>kidney bean. And that of S-114 was shown as pea>azuki bean>soy bean>kidney bean.
(2) These chemicals showed low selectivity and phytotoxicity less than pre-emergence treatment on post-emergence treatment. The descending order of the selectivity of S-113 was shown as pea>kidney bean>azuki bean≥soy bean, and that of S-114 was shown as pea=kidney bean=soy bean>azuki bean.
(3) In the field test, high adaptability were recognized as the pre-emergence treatment under 5g per are for soy bean, azuki bean, peanut and pea. In case of S-114 it was only pea plant.
(4) The relation between soil humidity and selectivity for crops was found to be fairly important. The selectivity decreased according to increase of soil humidity. As usually soil humidity in bean fields is 65 to 75%, these chemicals keep their selectivity even such condition.
(5) The movement in soil of S-113 and S-114 were less than bromacil, and the downward movement was from 2.5 to 4.5cm in silty clay loam soil, and from 6.5 to 9.5cm in sandy clay soil.
(6) The persistence in soil, both S-113 and S-114, were much stable as same as bromacil. The day for 50% decomposition of these chemicals were 70 to 80 days in sandy clay soil.
(7) Both S-113 and S-114 were much stable as same as bromacil to the decomposition by ultraviolet rays.

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