Tropical Agriculture and Development
Online ISSN : 1882-8469
Print ISSN : 1882-8450
ISSN-L : 1882-8450
58 巻 , 1 号
選択された号の論文の7件中1~7を表示しています
Original Article
  • David MAGUMBA, Atsushi MARUYAMA, Akira KATO, Michiko TAKAGAKI, Masao K ...
    2014 年 58 巻 1 号 p. 1-7
    発行日: 2014年
    公開日: 2014/04/09
    ジャーナル フリー
    In this paper, we estimate and identify, for Entebbe and Kampala areas on the northern shore of Lake Victoria as study areas, the present extent of Cyperus papyrus (papyrus) wetland and its change over time, using RapidEye (5 m resolution) and Landsat (30 m resolution) satellite images. We first estimated land cover for Entebbe area in 2010/2011 by using both RapidEye and Landsat images, second, the performance of Landsat in land cover classification was compared with that of RapidEye, and third, we identified changes in land cover in the last 15 years for the study areas by using Landsat images. The results of GIS analysis of RapidEye revealed that in 2011, 30% of Entebbe area was occupied by wetland, of which 70% was papyrus-covered. Between 1995 and 2010, the share of wetland decreased from 38% to 32% for Entebbe and from 15% to 11% for Kampala, but for both areas, the most decreases occurred in the last 5 years. Urban land use increased in Kampala from 17% to 64%, and from 9% to 23% for Entebbe, but for both areas, the type of land encroached first by the expanding urban land use was non-wetland vegetation, such as crop land, forest and green space, with relatively low encroachment on wetlands until the mid-2000s. However, urban expansion in recent years has reached a stage to encroach wetlands.
  • Soh SUGIHARA, Shinya FUNAKAWA, Kenta IKAZAKI, Hitoshi SHINJO, Takashi ...
    2014 年 58 巻 1 号 p. 8-17
    発行日: 2014年
    公開日: 2014/04/09
    ジャーナル フリー
    Soil carbon (C) and nitrogen (N) dynamics in the Sahel are primarily driven by intermittent rainfall, causing the wet-dry cycles of soil. We analyzed the relationship between in situ short-term C and N dynamics and hourly soil microbial dynamics during a wet-dry cycle in Niger cropland, in order to evaluate the effect of re-wetting of dry soil on soil C and N dynamics by conducting a field experiment in cropland. To reveal the local land management effect, we conducted the experiment in low C level croplands caused by the removal of plant residue for three years. Soil CO2 efflux and inorganic nitrogen were measured hourly and fluctuations in in situ microbial biomass and activity were measured using a simulated rainfall event (W plot) and a rainfall/glucose (WG plot) treatment. The rewetting of a dry soil did not clearly stimulate soil microbial dynamics, resulting in an unclear C flush (1.5 g C m–2 100h–1) and N mineralization in the W plot. This is possibly because the lack of plant residue application for three years caused a depletion of C substrate which should limit soil microbial biomass and activity during a wet-dry cycle. On the other hand, rainfall/glucose treatment had led to a clear C flush (3.6 g C m–2 100h–1) and distinct N immobilization mainly caused by increased microbial biomass after the treatment. Our results suggest the plant residue removal treatment easily degraded soil C levels, resulting in limited soil microbial dynamics during a wet-dry cycle, and a three-year period seemed to be long enough to cause this type of critical situation in this Sahel region.
  • Hirokazu HIGUCHI, Morio TSUKADA, Tomoko NINOMIYA, Takayuki FURUKAWA, A ...
    2014 年 58 巻 1 号 p. 18-25
    発行日: 2014年
    公開日: 2014/04/09
    ジャーナル フリー
    Insect pollination of cherimoya (Annona cherimola Mill.) was evaluated using artificially propagated Haptoncus ocularis, Mimemodes monstrosus, and Carpophilus marginellus beetles, which are some of the main insect visitors to cherimoya grown on the Japanese mainland. Among these species, both H. ocularis and C. marginellus proved to be good pollinators leading to more seed formation and better fruit set. The harvested fruits obtained following the release of either of these two species were similar in size to hand-pollinated fruits, although the release of C. marginellus led to a better fruit set than the release of H. ocularis. The release of these species at about five individuals per flower, or possibly less for C. marginellus, under ideal cool and humid environmental conditions may be sufficient for the effective pollination of cherimoya.
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