We investigated the mechanism of weed control by carp and the effect in growth and yield of paddy rice. Carp ate the soil with food materials and as a results carp mixed and agitated the surface of the soil. By the agitation, roots of the weeds were cut so that the weeds died. And more carp seemed to eat directly a part of weeds. We suggested that weeds production was inhibited by reduction of light penetration into soil surface. Because the water of paddy field was muddied by the agitation as the relative illuminance reduced by about 50% of non-carp plot. The deep flood irrigation for carp suppressed weed growth. Weed control was effective when carp were introduced in the field at early season (10-20 days after transplanting), long carp (10-15cm) were used and much more carp (>0.5 carp m^<-2>) were input. Compared to plot of non-carp, soil temperature was lower (about-1℃), and the number of stem decreased during the early season in the carp plot. However, there was not a difference in fruitful culms between both plots. Although the number of grain per head and of spiklets per ground increased in the carp plot, the grain yield decreased by reduction of percentage of ripened grain. We concluded that a discharge of carp could be used as effective weed control in paddy field, if the several conditions were prepared.

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[in Japanese]

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[in Japanese]

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The effect of root pruning on Na^+ exclusion in rice plant under NaCl-stress condition was investigated. Top Na content of KR1 and IR28 was increasad by pruning the tips of crown roots or branched roots. Na^+ exclusion rate, expressed as the TSCFNa^+, was decreased by root pruning. From these results, it was suggested that treatment solution was taken up into xylem with massflow through the cut surface. These results support the possibility that the sites of ion exclusion in rice root were mainly the exodermis and endodermis. Top Na content of young leaf increased by pruning of young roots. It showed that leaf Na content was closely affected by the root which belong to the same phytomer under saline condition.

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To investigate the influence of water deficit on the diurnal changes of net photosynthetic rate, transpiration rate, stomatal conductance and its any correlation, two Korean cultivars and one Japanese cultivar were grown in Wagner pots in phytotron. Treatment of soil moisture deficit was carried out by stopping irrigation 30 days after germination. Under soil-water deficit conduction, net photosynthetic rate, transpiration rate and stomatal conductance of the soybean plants were higher in the morning, but they decreased very quickly in broad day. Similar patterns of the diurnal changes were found with lower values day by day in the proceeding soil-water deficit. Plant water status recoverd net photosynthetic rates, transpiration rates of next morning to some extent, but it was effective under relatively mild water deficit condition. The water use efficiency (WUE) increased with decreasing soil moisture to 34% soil moisture, showing maximum value of WUE and decreased at levels over this content.

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Three soybean cultivars, Ohgon, Tanyou and Enrei were planted under field conditions to investigate the after effect of shading (50% of sun light) on the photosynthetic activity at three period in growth stages, i. e., flowering (shading in 43-68 days after emergence); pod formation (shading in 68-88 days after emergence) and maturity stages (shading in 92-109 days after emergence). The shading brought an increase in the length of petiole and stem except cultivar of Tanyou, but had no effect on the fully developed leaflet area on the first day of shading. The specific leaf area was increased and more at lower leaves than upper leaves by the shading treatment. The shaded plants had a higher value in leaf area per root dry weight as compared with the non-shaded plants. Shading treatment at the flowering stage decreased the net photosynthetic rate under saturated light after shading treatment in cultivars of Enrei and Ohgon. But the shaded leaf with treatment at the pod formation stage, showed similar rates to the control in phytosynthesis under saturated light. Shading at the maturity stage increased photosynthetic rates of leaves positioned on each part of the stem as compared with the non-shaded plants.

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It was reported in previous papers that the effect of shading treatment on photosynthetic rate (Pn) showed a differentiated growth stage. The present study was carried out in multiple regression analysis in order to determine the cause. The multiple regresion analysis showed that SLA was highly negative and leaf N% was positive in the period of flowering. For shading treatment at the pod formation, N% in leaf, SLA and leaf water potential (Wp) showed a higher correlation coefficient at r=0.818^<**>. The Pn was significantly correlated with N% in leaf of shaded and non-shaded plant at all shading treatments. The Pn in the treated plant was higher than in the control plant due to higher N% in the leaf. The shading treatment at maturity, stomatal conductance (Sc) decreased by 0.5cm/sec. An increase of Sc and Pn due to higher N% in the leaf by shading treatment was observed.

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