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Volume 46 (2001)
- Issue 4 Pages 261-
- Issue 3 Pages 169-
- Issue 2 Pages 91-
- Issue 1 Pages 3-
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Volume 46, Issue 4
Displaying 1-8 of 8 articles from this issue
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Hidehiro Inagaki, Yoko Oki2001 Volume 46 Issue 4 Pages 261-266
Published: January 30, 2002
Released on J-STAGE: December 17, 2009
JOURNAL FREE ACCESSWe examined experimentally the growth of corn and velvetleaf by changing the density of velvetleaf and obtained the following results.
1) We did not observe self-thinning of velvetleaf even at higher densities. At the highest velvetleaf density, 16 velvetleafs per corn plant (71.1 velvetleafs/m2), plant height of velvetleaf changed similarly to that of corn plant (Fig. 2). This suggested that light competition between corn and velvetleaf was intensified under this condition.
2) In the lowest density of velvetleaf, one velvetleaf plant per corn (4.4 velvetleaf/m2), the corn yield decreased about 20% compared to the control. The corn yield also decreased as the density of velvetleaf increased (Table 1).
3) The percentage of dry weight of velvetleaf per total dry weight of corn and velvetleaf had already been determined 40 days after corn sowing (Fig. 3) and seemed to be important in suppressing the growth of velvetleaf in early corn growth. Histograms of plant height overlapped between corn and velvetleaf at high densities (16 velvetleaf plants per corn plant). For low velvetleaf densities (one or four velvetleaf plants per corn plant), growth of velvetleaf was suppressed below the canopy layer of corn in spite of its density (Fig. 4).
4) For higher densities, velvetleaf capsules tended to be located in the upper layer of the community because of the mutual shielding. Therefore, the capsules produced per individual decreased (Table 2). Furthermore, under low-density conditions, the seed production per plant increased though the damage against the corn yield decreased (Table 2).View full abstractDownload PDF (586K) -
Ryuichi Sago, Hirokazu Takahashi, Shigeru Takayanagi2001 Volume 46 Issue 4 Pages 267-272
Published: January 30, 2002
Released on J-STAGE: December 17, 2009
JOURNAL FREE ACCESSDue to the increasing complexity of weed management, it is very important to develop a model for selecting the most effective weed management strategy. We established a method based on a weed seedbank and seedling density and estimated the thresholds of weed-seed density in which yield loss could be prevented.
The number of weed seeds and seedlings and the effect of weeds on rice yield were surveyed simultaneously at seven paddy rice fields in Ibaraki prefecture where the annual weeds dominated. The annual weeds that were found were primarily Lindernia spp., Cyperus spp., and Monochoria vaginalis (Burm. F) Kunth. The rates of established seedlings were 2.5% for Lindernia spp., 4.9% for Cyperus spp., 16.4% for Monochoria vaginalis and 5.2% for total weed seeds in 1.5cm/m2 of soil. However we could assume a seedling rate exceeding 3, 000 seeds in 1.5cm/m2 of soil. The loss of rice yield was negligible in rice paddy fields containing less than 3, 000 seeds in 1.5cm/m2 of soil.View full abstractDownload PDF (588K) -
T. Inamura, T. Yamamoto, H. Yoshida, T. Sugiyama, K. Nishio2001 Volume 46 Issue 4 Pages 273-281
Published: January 30, 2002
Released on J-STAGE: December 17, 2009
JOURNAL FREE ACCESSThe objective of this study was to investigate the effects of shading at several different stages of the tuber formation period on tuber production of Eleocharis kuroguwai Ohwi, a perennial paddy weed. In the experiment, plots with mixed planting of the weed and paddy rice were set in the paddy field. The plots were shaded at four different stages during the tuber formation period to control dry matter production and tuber production by suppressing the radiation absorbed by the weed.
After the shades were removed, the stem surface area (i. e., the assimilatory organ of the weed) did not increase during the rest of the tuber formation period (Fig. 3). The radiation absorbed by the weed was most conspicuously suppressed when the shading was conducted in the early tuber formation period (the first 15 days after the tuber initial stage) (Table 1). Therefore, tuber production was most severely suppressed by the shading in the early tuber formation period (Fig. 4). The tuber production was closely related to absorbed radiation during the early tuber formation period and through the tuber formation period (Table 3). The shortage of assimilated carbohydrates during the early tuber formation period reduced final tuber weight of the weed. These results suggest that a shortage of assimilated carbohydrates during the early tuber formation period defines potential tuber growth and determines final tuber weight.
We confirmed that shading in the early tuber formation period minimized tuber production and that the shortage of assimilated carbohydrates during the early tuber formation period was an effective control technique for suppressing the tuber reproduction of the perennial weed.View full abstractDownload PDF (1055K) -
Akira Koarai, Hidejiro Shibayama2001 Volume 46 Issue 4 Pages 282-290
Published: January 30, 2002
Released on J-STAGE: December 17, 2009
JOURNAL FREE ACCESSThe emergence of Monochoria vaginalis (Burm. f.) Kunth, Lindernia spp., Elatine triandra Schk. var. pedicellata Krylov, Rotala indica (Willd.) Koehne var. uliginosa (Miq.) Koehne, Ammannia multiflora Roxb., and Cyperus difformis L. was investigated in paddy soils kept under different moisture conditions before puddling and puddled in the middle of April, May, June and July in 1991 and 1992, respectively.
The number of emerged seedlings of weeds except for M. vaginalis and R. indica var. uliginosa increased in the soils under dry conditions from April to the puddling time, when the puddling time was delayed from April to July. The number of weeds remained almost constant in the soils under high moisture conditions from April to the puddling time, when the puddling time was delayed from April to July. The number was lower in soils under high moisture conditions during the ten-day period before puddling time than in the previous case. The number of M. vaginalis weeds was almost constant in paddy soils under different moisture conditions from April to the puddling time. The number of R. indica var. uliginosa decreased in paddy soils under different moisture conditions from April to the puddling time. Emergence pattern and emergence depth of the weeds were similar in paddy soils under different moisture conditions from April to the puddling time.View full abstractDownload PDF (835K) -
Hideaki Nakamura, Toshiyuki Kawamura, Masahiro Iwabuchi2001 Volume 46 Issue 4 Pages 291-295
Published: January 30, 2002
Released on J-STAGE: December 17, 2009
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2001 Volume 46 Issue 4 Pages 296-302
Published: January 30, 2002
Released on J-STAGE: December 17, 2009
JOURNAL FREE ACCESSDownload PDF (694K) -
Yasuhiro Yogo2001 Volume 46 Issue 4 Pages 303-307
Published: January 30, 2002
Released on J-STAGE: December 17, 2009
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Shinichi Shirakura, Hiroyuki Kobayashi, Akihide Fushimi, Akira Koarai2001 Volume 46 Issue 4 Pages 315-318
Published: January 30, 2002
Released on J-STAGE: December 17, 2009
JOURNAL FREE ACCESSDownload PDF (468K)
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