Masao Arai

On the Phytotoxicity of Several Herbicides to Young Seedlings and Weeds in Transplanting Rice Culture

水稲稚苗移植栽培の初期雑草対象除草剤を選定するために, ポット試験および圃場試験に各種除草剤を供試して殺草性について検討した。CNP粒剤およびNIP粒剤は, 田植前後の表面処理でマツバイに対する除草効果がやや劣るが, 一年生雑草には効果が大きい。稚苗に対する薬害はCNPおよびNIPとも比較的小さいが, 薬害発生の危険性は, NIPがCNPより大きい。CNPは適使用量幅が広く, 田植前土壌混層処理剤としても比較的安定している。TOPE粒剤は, 田植後処理でマツバイに効果がやや劣るが, 一年生雑草には除草効果が大きく, CNPやNIPよりも処理適期幅が広い。薬害発生の危険性はCNPよりさらに小さい。シメトリン粒剤は, 田植後処理で一年生雑草に除草効果が大きく, 残効期間も長いが, マツバイにはやや劣る。薬害は使用量が多いと発現するが, 水深・漏水条件によっても変動するおそれがある。TDW-43・シメトリンA粒剤は, 田植前・後の表面処理でマツバイ以外には除草効果が大きいが, シメトリンの薬害が発生する条件下では薬害発生の危険性がある。その他の供試除草剤については, 稚苗に対する薬害の面からさらに検討を要する。

Studies on Selective Toxicity of Soil-incorporated Swep [Methyl-N-(3, 4-dichlorophenyl) carbamate, MCC] to Rice Plant and Barnyardgrass at the Germinating Stage

水稲の乾田直播栽培の乾田期間・畑苗代および畑稲の雑草防除に極めて有効な除草剤MCCの土壌処理における適切な処理方法を明らかにするために, 発芽時地下部処理におけるタイヌビエ・水稲間の選択殺草性を究明する数多くの実験を行ない, 次の知見が得られた。MCCの発芽時地下部処理における水稲・タイヌビエに対する殺草力は根部より幼芽部において著しく大きい。 したがつて殺草作用部位は根部にもあるが幼芽部の方がより大きい。 しかも, 殺草力は幼芽部・根部ともに水稲よりタイヌビエに対して大きく, タイヌビエ>水稲の選択殺草性程度は中～大である。この選択殺草性の発現部位が幼芽部にあるか根部にあるかという, いわゆる選択殺草性の発現作用部位は, 根部にもあるがその程度は小さく, 主として幼芽部にある。 しかも同じ幼芽部でも, 発芽直後の幼芽より, ある程度伸長した幼芽に処理した方が選択殺草性は顕著である。以上の関係から, MCCは稲を播種し, 1.5-3.0cmに覆土して後に, 土壌表面に処理するのが最も安全効果的な使用法である。さらに前報で明らかにしたように, 本剤は土壌処理効果とともに雑草処理効果も極めて大きく, 反面1葉展開以後の稲には薬害が大きいので, その処理時期は播種直後から稲の出芽期までであるが, 本研究によつてこの期間中における土壌処理の安全性を立証した。

Optimum Application Time of MCC [Methyl-N-(3, 4-dichlorophenyl) carbamate; Swep] in Dry-seeded Rice Culture

水稲に対して, 播種後～1葉展開前の処理では薬害はない。2.0葉期・3.0葉期の処理では著しい薬害を生ずる。ノビエに対する土壌処理効果は, 発生抑制および生育抑制として現われ, 残効期間は50g/aで2～3週間程度とみられる。雑草処理では, 50g/a の薬量で3.5～4葉までのノビエをほぼ完全に枯殺する。ノビエ以外の一年生雑草にも, 全般に高い土壌処理効果・雑草処理効果を有する。乾田直播栽培におけるMCCの処理可能時期は, 水稲播種後～出芽期 (1葉展開前) である。雑草の発生期間が長いことを考慮に入れると, 出芽期の処理が最も合理的である。その場合, 40～50g/aの薬量で, 抑草期間は播種後25日前後とみられる。PCP, NIP などの播種後処理にくらべると, 処理適期幅の長いことや除草効果の高い点ですぐれている。しかし, 乾田期間の短いときや雑草の発生が初期に集中するときなどの場合を除いて, MCCのみで乾田期間発生雑草を防除することは難かしく, 一般的にはDCPAとの結合が必要である。

Studies on Chemicals Effective for Breaking Seed-dormancy and for Killing Dormant Seed of Barnyardgrass (Echinochloa Crus-galli Beauv. var. oryzicola Ohwi) : 3. Activity of several chemicals used in contact with soil

Effectiveness of four chemicals, NIP (2, 4-dichlorophenyl-4-nitrophenyl ether), 1-isothio-cyanato-2-bromopropene (U-3), 1-thiocyanato-2-bromopropene (U-4) and DNBP (4, 6-dinitro-o-sec-buthylphenol), which showed high activity in the soaking treatment, was examined under the presence of soil using petri-dishes or 1/5000 a pots. Three methods were used for the treatment: spraying of the chemical solution to the seeds placed on the surface of water-drained soil, applying of the chemical solution to the seeds placed on the surface of water-submerged soil, and incorporating of the chemical solution to the upper layer of water-drained soil with the seeds. The results obtained were as follows: 1. Effectiveness of each chemical varied according to the method of treatment. NTP, U-3 and U-4 were more effective in the following cases: in case the effect of breaking dormancy by the method of treatment itself was higher, or in case the concentration of chemical solution in contact with the seeds was higher. This fact was especially remakable in NIP. DNBP was most effective when it is sprayed directly to the seeds. 2. The effectiveness in these treatments in contact with soil, in general, was markedly less than in the soaking treatment. Therefore, it was assumed that the treatment given under the presence of soil might have several factors decreasing the activity such as the adsorption and decomposition by soil or the vaporization of chemicals. 3. Generally speaking, such dosages as above 400 g/a in NIP, 200 g/a in U-3 or U-4 and 400 g/a in DNBP were required for full activity. 4. In order to establish the technique for breaking the dormancy or for destroying the germinability of dormant barnyardgrass seeds in soil by chemicals, it is important to find out not only chemicals with higher activity but also methods or factors which will improve the permeability of such chemicals into the seeds.

Physiological and Ecological Studies on Barnyard Grass (Echinochloa crus-galli Beauv. var. oryzicola Ohwi) : V. On the germination of the seed.

The emergence of barnyard grass seeds is divided into two processes, that is, germination in soils and elongation of plumule through soils after germination. The former process was studied in the present report. 1) Maximum, optimum and minimum temperatures for germination were 45°C, 30°to 35°C and 10°C to 15°C respectively. The completely after-ripened seeds were not accelerated under the alternating temperature condition. 2) The seeds were able to germinate with pH ranging from 4.7 to 8.3. So, it was concluded that this plant was adaptable to soil acidity for the germination. 3) Oxygen tension of 20 per cent (air) was favorable for germination. But, germinaion percent was decreased in the oxygen tension below 1 per cent. 4) Germination did not occure in water contained 1×10-3M KCN and NaN3, while not affected DICA, MIA and 8-hydroxyquinoline. Therefore, we thought that cytochrome oxidase played an important role in the process of germination of barnyard grass seeds. 5) Soil water content influenced the germination of the seeds, and 70 to 95 per cent soil moisture content of field capacity was optimum for germination. 6) Germination per cent of the seeds in the submerged soil varied with Eh values of the soil. In the below 350 to 400 mV of Eh6 of the soil, germination per cent decreased according to the fall of Eh value, and hardly germinated in the soils below 100 mV of Eh6. 7) As the results of these findings, germination of seeds were good in the field of the wet upland condition (above 70 per cent soil moisture content of field capacity) in which Eh value was kept high. And, dry upland soil condition and submerged soil condition with low Eh value were unfavorable to germination.

Physiological and Ecological Studies on Barnyard Grass (Echinocloa crus-galli BEAUV. var. oryzicola OHWI) : II. On the primary dormancy of the seed. (2) On the dormancy broken of the seed in the soil.

The present report deals with the primary dormancy of seeds of barnyard grass in the soil, and the results are as follows: Under the room-temperature condition, the dormancy of the seeds were broken in a shorter period under storage in upland or submerged soil condition than on the dry or wet filter paper. The dormancy of the seeds stored in a paper bag at room temperature lasts about one year after harvest. The period of dormancy of seeds in the soil varied according to the temperature and moisture content of the soil. In the storage at lower temperature (3∼5°C) than germination temperature, process of the dormancy breaking progressed in all moisture content, and the speed of progress was faster at high moisture content. In the storage at optimum temperature for germination (20∼30°C), deep dormant seeds were awakened slowly in the air dry soil, but not awakened in submerged or upland soils untill about ten months after harvest. However, partially dormant seeds (no germination at germinator) were awakened from the dormancy rapidly by the storage in submerged soils, but were reinduced to dormancy by the storage in upland condition (soil moisture content 70 to 80 per cent of the field moisture capacity). Storage treatment in submerged soil was very effective to breaking the dormancy, if the seeds were already awakened from dormancy up to some degree by storage for 15 days or more at low temperature with wet condition. Optimum period and temperature for the storage treatment in submerged soil were varied with degree of dormancy. The shallower dormant seeds were awakened from dormancy with shorter period storage at various range of temperature (5°to 40°C), but in relatively deep dormant seeds the dormancy was broken after longer period storage at high temperature (30°C to 40°C). The cause of dormancy broken by storage treatment in submerged soil is the low oxygen content in the soil because the similar effects obtained from the storage treatment of seeds in nitrogen gas. Seeds that awakened from dormancy in the soils were reinduced to dormancy with air dry treatment. As the results of these findings, it was clarified that processes of the dormancy breaking were divided in five, and low temperature during from late autumn to early spring, alternating temperature in spring and submergence at the start of rice culture were important for breaking the primary dormancy of the seeds in paddy field.

Changes of Weed Communities by Methods of Cultivation in Winter Cropping on Drained Paddy Fields : (1) Influence of plowing time on the structure of weed communities and the quantity of weeds

1) The structure of weed community was changed with plowing time. The quantity of weeds decreased strikingly as the plowing time was delayed (Fig. 1). The relative intensity of influence of two factors (viable seeds population and emergence percentage) on the population of emergence was varied (Fig. 2). As the plowing is delayed, decrease in emergence percentage becomes more influencial in decreasing weed population, because the emergence percentage is closely related with air temperature (Fig. 3). 2) As the growth and yield of wheat are found to be scarcely effected by the delay of seeding time, it can be an effective method of weed control in wheat and barley cultivation in warm regions to regulate the seeding time according to the weed-density.