The purpose of this experiment was to establish the spreading method of granular herbicides by boom-spreader with spout nozzles in paddy fields. The results obtained were as follows;
1. It influenced upon neither the efficacy of weed control nor the growth of rice plants to spread granular herbicides by this method.
2. This spreader could be used satisfactorily at less than three metres per second of wind velocity, when it was not rainy.
3. The shutter and the revolution of blower must be adjusted adequately according to the granule size of a herbicide, and the boom have to be carried at as constant a speed as possible in order to get uniform spreading.

View full abstract

Optimum conditions for germination of Amaranthus viridis seeds were studied.
1. With conc. sulfuric acid the treatment (about 2min.) of seeds raised the germination percentage to three times that of the untreated.
2. Optimum temperature for germination was 35°, and then it was about 100 percent. With the fall of temperature, the germination percentage was lower. Under optimum temperature the treatment with sulfuric acid was not effective but under the lower temperature its effect was remarkable.
3. Gibberellin was not effective on the germination of seeds.

View full abstract

Effect of the three principles of fertilizers and the amount of nitrogen on the growth and chlorophyll content of Amaranthus viridis during cultivation was examined.
1. Although the considerably worse effects of lack of nitrogen and phosphate were observed, the effects caused by potash in fertilizer seemed very slight.
2. With the increase of amount of nitrogen in fertilizer, the growth, the content of chlorophyll and the yield tended to become higher.

View full abstract

This study was conducted in an attempt to make clear the effect of temperature on emergence and growth of perennial weeds, Cyperus serotinus Rottb. and Sagittaria pygmaea Miq. in paddy field and to establish the way to control them effectively with chemicals. The results obtained are summarized as follows.
1) On Cyperus serotinus Rottb., it was able to presume the emergence time from the accumulated value of the daily mean air-temperature, when the mean-temperature at puddling time was above 15°C. That is, the value amounted to about 42°C at the time when the percentage of emergence was 20%, about 65°C at the time when it was 50%, and about 85°C at the end of emergence. However, on Sagittaria pygmaea Miq., the earlier the puddling time was, the slower the emergence rate was, and therefore, it was unable to presume it.
2) The earlier the puddling time was, the slacker the growth after the emergence of both plants was, and the longer the stagnated period of growth was.
3) It was recognized a certain relation between the number of days required for attaining to the fixed leaf stage after puddling and mean air-temperature in this period, within the limits of 14°-25°C on Cyperus serotinus Rottb., and 16°-24°C on Sagittaria pygmaea Miq.. These results will be useful to presume the variation of the leaf emergence rate at the different puddling time.
4) From the results above-mentioned, the effective period of treatment with herbicides after transplanting of rice plant was discussed.

View full abstract

The present investigation was undertaken to make clear the relation between seed development and germination behavior of Rumex obtusifolius L. during maturation in field. The following four developmental phases during seed maturation could be recognized by critical analysis of temperature range for germination, and dry weight increment and moisture loss of seed.
The first phase covered stage flowering to about one half of dry weight of mature seed. At this phase, seed showed high moisture content, above 70%, and was not viable. The second phase was characterized by linear increase in dry seed weight, reaching a maximum weight of seed at the end of the phase. The moisture content was still at high level of above 60%. During this phase, germination occurred within comparatively wide temperature range. The third phase was characterized by rapid decrease of moisture content of seed. During this period, germination percent at higher temperatures declined, resulting in a restricted temperature range for germination. The last fourth phase covered the remaining period after the third phase. The seed gradually recovered the ability to germinate at relatively high temperatures.

View full abstract

As to the secondary succession of weed vegetation in no-cultivated well-drained paddy fields, communities dominated by E. sumatrensis were established in the second year of no-cultivation. However, this species began to disappear rapidly in the third year. In order to elucidate the above mentioned phenomena, effects of the relative illuminance and dead roots of this species on the germination of seeds and the growth of seedlings were investigated.
(1) The relative illuminances (that is, 100, 15.5, 6.0, 2.5, 1.0 percent) did not affect in the germination but affected the growth of seedlings. The growth of seedlings was maximum under 15.5% illuminance. Thirty days after germination, seedlings under 15.5% and 100% illuminances developed into rosette type. Under the other illuminances, seedlings did not grow to rosette type but spindly growth type and they were stunted in growth extremely.
(2) There appear to be existed some phytotoxic substances in the roots or the root decompositing products of E. sumatrensis. These substances inhibited the growth of seedlings, especially radicles, of E. sumatrensis and E. linifolius, and induced the negative geotropism of radicles. The higher the concentration of these substances was, the stronger these effects were. Moreover, under the same concentration, the substances of adult plant roots included in soil showed the inhibitive effect on the growth more than the inductive effect of negative geotropism of radicles. The effects, however, were reverse in substances of rosette type plant roots. Therefore, these two effects may be controlled by two different substances. These substances did not affect in the germination. There found same effects above on the tests when added to the seeds with aqueous substances which extracted from the dead roots, E. linifolius also contained the same substances in its roots.
(3) Besides, when more than 4% of the dead roots were addes to soil weight, all the seeds (achenes) which germinated early in October developed into small seedlings with 2-3 leaves of non rosseted at the end of December, and then these individuals with 2-3 leaves had died outdoors in winter by the middle of February.
(4) In E. Sumatrensis-community which is established in the second year of no-cultivation, the relative illuminance decreases and its own roots accumulate at the time of germination of next generation. Therefore, the growth of seedlings of next generation is inhibited and the nagative geotropism is induced, then these seedlings die in winter. Therefore, E. sumatrensis begins to disappear rapidly from the third year of no-cultivation.

View full abstract