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Volume 58, Issue 4
Displaying 1-4 of 4 articles from this issue
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Serrie KAMARA, Tilack KURUPPUARACHCHI, Edmond Ranga RANATUNGE, Yousay ...2002 Volume 58 Issue 4 Pages 171-183
Published: December 10, 2002
Released on J-STAGE: February 25, 2010
JOURNAL FREE ACCESSA study of the seasonal structure of rainfall organization in a humid tropical mountain region of West Africa using multivariate classification techniques revealed considerable variations in rainfall regimes from ultra-humid to sub-humid conditions. Principal Component Analysis produced a three-component model which was used to characterize and explain the seasonal rainfall variations within the region. These are the Dry Season component which accounts for most of the variance in the rainfall data and represents the December-April period; the Wet Season component (June-September) and the Wet/Dry and Dry/Wet transitions component in October-November and May, respectively. Using the three components and a hierarchical clustering procedure, seven clusters representing the rainfall regimes were identified and characterized. A better understanding of the regional rainfall climate is important to West African countries whose economies depend largely on agriculture and related activities governed by the reliability of rainfall.View full abstractDownload PDF (3015K) -
Yasuyuki WAKIYAMA2002 Volume 58 Issue 4 Pages 185-194
Published: December 10, 2002
Released on J-STAGE: February 25, 2010
JOURNAL FREE ACCESSInfrared remote sensing is used for crop monitoring, for example evaluation of water stress, detection of infected crops and estimation of transpiration and photosynthetic rates. This study was conducted to show another application of remote sensing information. The relationship between rice leaf temperature and chlorophyll content in the leaf blade was investigated by using thermography during the ripening period. The canopy of a rice community fertilized by top dressing was cooler than that not fertilized in a 1999 field experiment. In an experiment using thermocouples to measure leaf temperature, a rice leaf with high chlorophyll content was also cooler than that with a low chlorophyll content. Transpiration resistance and transpiration rate were measured with a porometer. Transpiration rate was higher with increasing chlorophyll content in the leaf blade. Stomatal aperture is related to chlorophyll content in the leaf blade. High degree of stomatal aperture is caused by high chlorophyll content in the leaf blade. As degree of stomatal aperture increases, transpiration rate increases. Therefore the rice leaf got cooler with increasing chlorophyll content in leaf blade. Paddy rice communities with different chlorophyll contents were provided with fertilization of different nitrogen levels on basal and top dressing in a 2000 field experiment. Canopy temperature of the rice community with high chlorophyll content was 0.85°C cooler than that of the rice community with low chlorophyll content. Results of this study revealed that infrared remote sensing could detect difference in chlorophyll contents in rice communities and could be used in fertilizer management in paddy fields.View full abstractDownload PDF (1290K) -
Hitoshi YOKOYAMA, Masaaki KISO, Yoshinobu HARAZONO2002 Volume 58 Issue 4 Pages 195-206
Published: December 10, 2002
Released on J-STAGE: February 25, 2010
JOURNAL FREE ACCESSLeaves of leather fern are used as a foliage plant and Mottled Yellowing Syndrome (MYS) has been occurring on leaves cultivated in protected greenhouses at Hachijo Island since the 1990s. Experiments with different shading levels and soil moisture levels were carried out to develop cultivation methods that will prevent the occurrence of MYS. Relationships between the greenhouse environment and the occurrence of MYS were examined and the following results were obtained.
The temperature of air, the canopy surface, and soil in the greenhouses were affected not only by shading levels but also by the color of the shading net. Air and canopy surface temperature decreased with an increase of shading rate with blue nets, however, temperatures under black nets were quite high due to the high surface temperature of the nets, which caused a high occurrence of MYS.
Numbers of leaves decreased with an increase of shading level, but the leaf size increased. Chlorophyll content of the leaves increased with shading levels too.
An optimum greenhouse environment to increase leaf size, leaf number, and chlorophyll content was obtained by a using a blue net with a 55% shading rate and the soil water potential controlled to less than 0.016MPa.
MYS occurrence is increased by high temperature stress of the plant rather than high solar radiation in greenhouses. Also, MYS occurrence was decreased by frequent irrigation.
MYS occurrence (%) can be estimated by degree days over 34°C of maximum air temperature for well-irrigated greenhouses, and by 1.5 times the degree days over 32°C for less-irrigated greenhouses. Farmers can manage the greenhouse environment to reduce MYS damage by applying these results.
Greenhouses devoted to leather fern cultivation should be shaded (around half the amount of sunlight compared to outside) and should be controlled to keep good ventilation and soil moisture by frequent irrigation, which provides a desirable canopy surface-, air- and soil temperature, resulting in reduction of MYS damage and improvement in productivity and quality.View full abstractDownload PDF (5076K) -
Tatsuo HOSONO, Norio HOSOI2002 Volume 58 Issue 4 Pages 207-216
Published: December 10, 2002
Released on J-STAGE: February 25, 2010
JOURNAL FREE ACCESSInformation on water uptake by plants is useful for management in greenhouse cultivation (e.g. irrigation control). In this paper, we continuously measured water uptake by long-term tomatoes grown in a re-circulating hydroponic system in a glasshouse through two entire cultivation periods (Each cultivation period was 9-10 months long, from mid-winter to mid-summer). Amount of water uptake by plants was measured by monitoring the amount of water supplied to the hydroponic system. Over 95% of total water uptake by the plants throughout cultivation period was passed through the plants as transpiration. Daily amount of water uptake increased with the increase of leaf area until LAI reached 1.5, then was not significantly affected by LAI. Day-by-day change of daily water uptake amount was primarily associated with change of daily-accumulated solar radiation. Daily water uptake amount by long-term tomatoes was well estimated by a multiple regression equation including daily-averaged air temperature and water vapor pressure deficit in glasshouse in addition to daily-accumulated solar radiation as independent variables.View full abstractDownload PDF (1331K)
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