Research for Tropical Agriculture
Online ISSN : 2187-2414
Print ISSN : 1882-8434
ISSN-L : 1882-8434
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Original Article
  • Koji UCHINO, Koji IWATA, Hitoshi KUKITA, Osamu KUMAMOTO
    2019 Volume 12 Issue 2 Pages 59-64
    Published: 2019
    Released: July 02, 2020

    In order to obtain large size fruit, the relationship between fruit weight and flowering date, and number of fruit per cluster and cumulative temperature in ‘Natsutayori’ loquat (Eriobotrya japonica (Thunb.) Lindl.) were investigated. The mean fruit weight exceeded 60g when flowering from mid-November to the beginning of January, but took place at its smallest when it occurred in mid-January. The fruit weight was slightly larger in the two fruit per cluster than in the 3 and 4 fruit per cluster. As the flowering date became later, the fruit shape index increased, and consequently the shape of its longitudinal section became circular from a short oval one. Both the number of days to ripening and the cumulative temperature, based on 0℃ from flowering to ripening quadratically, correlated with the fruit weight, which was at its largest, when the number of days to ripening and the cumulative temperature, based on 0℃, was 145-160 days and 1,750-1,900℃・day, respectively. When the threshold temperature of the cumulative temperature was changed from 0 to 13℃, the coefficient of variance was the smallest at 10℃, with a cumulative temperature of 532℃・day.

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    2019 Volume 12 Issue 2 Pages 65-72
    Published: 2019
    Released: July 02, 2020

    Saline irrigation water is a stress factor that can reduce crop productivity; yet, limited information regarding water salinity in sugarcane production areas and its effects on sugarcane is available in Japan. Therefore, we first analyzed water samples collected from 54 locations on six islands and found that Cl- and Na+ were the primary ions in irrigation water. The ion concentrations varied depending on the sampling locations and the types of water source: most reservoirs showed total ion concentrations below 500 mg L-1, while the highest exceeding 2500 mg L-1 was obtained in a natural swamp on Minamidaitoujima, where brine was considered to merge underground. Secondary, sugarcane was cultivated with water containing up to 3000 mg NaCl L-1. The saline waters tended to decrease sugarcane height and leaf number; however, no harmful effects were observed at harvest when the NaCl levels were up to 500 mg L-1. Meanwhile, the saline waters with 1000 mg NaCl L-1 or higher resulted in significant reductions in stem and leaf dry weights as well as sugars in juice. A regression analysis using data sets of total ion concentration and electrical conductivity (EC) from the survey as independent and dependent variables, respectively, revealed the coefficient of determination being 0.995, suggesting the possibility to accurately grasp water salinities through easy EC measurements. Taken together, it was concluded that sugarcane could be damaged by salt stress in fields where EC of irrigation water is over 250 mS m-1.

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  • A comparison of Ahero irrigation scheme and out-growers
    Yuko YAMANE, Yoko ICHIJO, Syuichi ASANUMA
    2019 Volume 12 Issue 2 Pages 73-91
    Published: 2019
    Released: July 02, 2020

    In this study, we analyzed the rice cultivation and management in the irrigation schemes of the National Irrigation Board (NIB) and in three small schemes managed by local farmers so called outgrowers, which are distributed near the Lake Victoria in Western Kenya. As a result, we found big differences between NIB schemes and outgrowers’ schemes in their farm size and production. In NIB scheme, the average farm size per household was approximately one hector and their yield was 4.5 kg ha-1 which is double size and 1.5 times higher yield comparing outgrowers. Our survey suggests that this higher yield is brought by large amount of fertilizer and pesticide input and also appropriate frequency and timing of weeding. Necessarily, total production of NIB farmers is bigger, and they succeeded to sale about 3.5 ton per household, whereas outgrowers achieved only around 30% of it. The expenditure for rice cultivation of NIB farmers was about twice as large as outgrowers, but due to their big sales volume, their cash income from rice production after removing production cost at least 5 times and at most 26 times of outgrowers’. In all schemes, labor costs was the major component of management expenses. Outgrowers spent for wage labors, while they paid small cost for fertilizer and agricultural chemicals. Additionally, to meet this cash demand, many of them sold their livestock which was their important assets.

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  • Haruyuki DAN, Yoko OKI, Shinji HIROUCHI
    2019 Volume 12 Issue 2 Pages 92-99
    Published: 2019
    Released: July 02, 2020

    In the inland valleys of Ghana, where a great deal of research and development towards boosting rice production is being promoted, the low ratio of irrigated rice fields and the aging of existing irrigation facilities pose problems for rice production. In developing reinforcement technology, using cover plants for irrigation facilities in paddy fields, it is a requisite to establish control methods against the overgrowth and invasion of introduced-plant communities. Some expriments on slashing by cutlass, focusing on weed suppression and eradication methods and making it easier for farmers to practice this themselves, were conducted. There was no difference in herbicidal effects between treatments with or without such slashing before herbicide application with 200mL m-2 in a 50-time dilution of glyphosate, propanil and butachlor. An application of these three herbicides suppressed only the parts of the following three test plants above ground from 2 weeks to 4 months, so falling short of eradicating them completely. It was found that by putting the test plants in a flooded environment for two months immediately after slashing, Cynodon dactylon was unable to regrow healthily within 2 weeks, and both Chrysopogon aciculatus and Stenotaphrum secundatum were able to be eradicated all together. Moreover, slashing by cutlass is effective as a weed control technology if the plant height was at 1 cm. In addition, the eradication of these plants is possible by this method several times on the ground surface within 2 months of establishment.

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