Kyushu University Academic Staff Educational and Research Activities Database
List of Papers
Yuichiro Fujioka Last modified date:2020.03.17

Lecturer / Department of Environmental Changes / Faculty of Social and Cultural Studies

1. Yoshinori Watanabe, Fisseha Itanna, Yasuhiro Izumi, Simon K. Awala, Yuichiro Fujioka, Kenta Tsuchiya, Morio Iijima, Cattle manure and intercropping effects on soil properties and growth and yield of pearl millet and cowpea in Namibia, Journal of Crop Improvement,, 33, 3, 395-409, 2019.04.
2. Yuichiro Fujioka,Yoshinori Watanabe,Hiroki Mizuochi,Fisseha Itanna,Shou Ruben,Morio Iijima, Classification of Small Seasonal Ponds Based on Soil–Water Environments in the Cuvelai Seasonal Wetland System, North-Central Namibia, Wetlands, 10.1007/s13157-018-1073-y, 38, (5), 1045-1057, 2018.11, The objectives of this study were to classify the small seasonal ponds that develop in the Cuvelai Seasonal Wetland System in north-central Namibia based on soil physicochemical properties so that potential agricultural uses of the ponds could be assessed. Satellite imagery was used to examine the relationships between soil characteristics and the probability of water presence in the region. Soil samples were collected from 66 ponds at three sites and their physicochemical properties and levels of salt accumulation were investigated. Soil data were analyzed by using principal component analysis and cluster analysis. The ponds were classified into four types based on soil properties. Type A accounted for 20% of the ponds and was characterized by high levels of clay, silt, total N, and exchangeable Ca, Mg, and K. Type B accounted for 14% of the ponds and was characterized by high values of organic C, C/N ratios, and available P. Type C accounted for 20% of the ponds, and this type featured high levels of salinity and sodicity. The remaining ponds were classified as Type D. If these seasonal ponds are to be considered for crop production, Type C should be avoided and Type D would require soil fertility improvements..
3. Hiroki Mizuochi, Tetsuya Hiyama, Takeshi Ohta, Yuichiro Fujioka, Jack R. Kambatuku, Morio Iijima, Kenlo N. Nasahara, Development and evaluation of a lookup-table-based approach to data fusion for seasonal wetlands monitoring
An integrated use of AMSR series, MODIS, and Landsat, Remote Sensing of Environment, 10.1016/j.rse.2017.07.026, 199, 370-388, 2017.09, Broad scale monitoring of inland waters is essential to research on carbon and water cycles, and for application in the monitoring of disasters including floods and droughts on various spatial and temporal scales. Satellite remote sensing using spatiotemporal data fusion (STF) has recently attracted attention as a way of simultaneously describing spatial heterogeneity and tracking the temporal variability of inland waters. However, existing STF approaches have limitations in describing abrupt temporal changes, integrating “dissimilar” datasets (i.e., fusions between microwave and optical data), and compiling long-term, frequent STF datasets. To overcome these limitations, in this study we developed and evaluated a lookup table (LUT)-based STF, termed database unmixing (DBUX), using multiple types of satellite data (AMSR series, MODIS, and Landsat), and applied it to semi-arid seasonal wetlands in Namibia. The results show that DBUX is: 1) flexible in integrating optical data (MODIS or Landsat) with microwave (AMSR series) and seasonal (day of year) information; 2) able to generate long-term, frequent Landsat-like datasets; and 3) more reliable than an existing approach (spatial and temporal adaptive reflectance fusion model; STARFM) for tracking dynamic temporal variations in seasonal wetlands. Water maps retrieved from the resulting STF dataset for the wetlands had a 30-m spatial resolution and a temporal frequency of 1 or 2 days, and the dataset covered from 2002 to 2015. The time series water maps accurately described both seasonal and interannual changes in the wetlands, and could act as a basis for understanding the hydrological features of the region. Further studies are required to enable application of DBUX in other regions, and for other landscapes with different satellite sensor combinations..
4. Tetsuya Hiyama, Hironari Kanamori, Jack Kambatuku, Ayumi Kotani, Kazuyoshi Asai, Hiroki Mizuochi, Yuichiro Fujioka, Morio Iijima, Analysing the origin of rain- and subsurface water in seasonal wetlands of north-central Namibia, Environmental Research Letters, 10.1088/1748-9326/aa5bc8, 12, 034012, 2017.03, We investigated the origins of rain- and subsurface waters of north-central Namibia's seasonal wetlands, which are critical to the region's water and food security. The region includes the southern part of the Cuvelai system seasonal wetlands (CSSWs) of the Cuvelai Basin, a transboundary river basin covering southern Angola and northern Namibia. We analysed stable water isotopes (SWIs) of hydrogen (HDO) and oxygen (H2 18O) in rainwater, surface water and shallow groundwater. Rainwater samples were collected during every rainfall event of the rainy season from October 2013 to April 2014. The isotopic ratios of HDO (δD) and oxygen H2 18O (δ 18O) were analysed in each rainwater sample and then used to derive the annual mean value of (δD, δ 18O) in precipitation weighted by each rainfall volume. Using delta diagrams (plotting δD vs. δ 18O), we showed that the annual mean value was a good indicator for determining the origins of subsurface waters in the CSSWs. To confirm the origins of rainwater and to explain the variations in isotopic ratios, we conducted atmospheric water budget analysis using Tropical Rainfall Measuring Mission (TRMM) multi-satellite precipitation analysis (TMPA) data and ERA-Interim atmospheric reanalysis data. The results showed that around three-fourths of rainwater was derived from recycled water at local–regional scales. Satellite-observed outgoing longwave radiation (OLR) and complementary satellite data from MODerate-resolution Imaging Spectroradiometer (MODIS) and Advanced Microwave Scanning Radiometer (AMSR) series implied that the isotopic ratios in rainwater were affected by evaporation of raindrops falling from convective clouds. Consequently, integrated SWI analysis of rain-, surface and subsurface waters, together with the atmospheric water budget analysis, revealed that shallow groundwater of small wetlands in this region was very likely to be recharged from surface waters originating from local rainfall, which was temporarily pooled in small wetlands. This was also supported by tritium (3H) counting of the current rain- and subsurface waters in the region. We highly recommend that shallow groundwater not be pumped intensively to conserve surface and subsurface waters, both of which are important water resources in the region..
5. Koki Teshirogi, Chisato Yamashina, Yuichiro Fujioka, Variations in mopane vegetation and its use by local people: Comparison of four sites in northern Namibia, African Study Monographs, 10.14989/218898, 38, 1, 5-25, 2017.03.
6. Yoshinori Watanabe, Fisseha Itanna, Yuichiro Fujioka, Shou Ruben, Morio Iijima, Soil fertility status of seasonally closed wetland ecosystem (ondombe) in north-central Namibia, African Journal of Agricultural Research, 10.5897/AJAR2017.12235, 12, 18, 1538-1546, 2017.02, [URL], In the Cuvelai Seasonal Wetland System (CSWS) of North-central Namibia, there are widespread manifestations of seasonally flooded river and seasonally closed wetland ecosystems (ponds). These wetlands are called oshana (seasonally flooded river wetland) and ondombe (seasonally closed wetland) according to the local language. This study was initiated to find out the soil fertility status of ondombes and whether they could be utilized for agricultural purposes unlike the present situation. Soil salinity and sodicity were determined to find out impact of such adverse conditions on possibility of food production. A total of 70 representative ondombes were identified from three selected villages. A total of 210 soil samples were collected from upper, middle and lower positions adjacent to ondombes, and 15 soil samples from each 5 upland fields in the three villages and 102 soil samples from different spots of the flood plain in the three oshanas for comparison. The results indicated that the mean soil pH (H2O) in ondombe was 6.3, the means of organic C and total N were 6.28 and 0.41 g kg-1; respectively, the mean of available P was 4.81 mg P kg-1. The means of exchangeable Ca, Mg, K, and Na in ondombe were 2.31, 1.44, 0.21, and 0.61 cmolc kg-1, respectively. Most soil nutrients were higher in lower ondombe positions than on upper and middle positions. Organic C, exchangeable Mg, and clay at the ondombe soils were significantly higher than those at the croplands. The means of electrical conductivity of saturation extract (ECe) and sodium adsorption ratio (SAR) in ondombe soils were 0.62 ds m-1 and 7.32, respectively; even though most of the ondombe soils did not exhibit salinity and sodicity problems. Hence, one can conclude that an ondombe soil has an appropriate condition for agriculture, and may
only be prone to sodicity whenever the sodium content is high, as sometimes observed..
7. Yoshinori Watanabe, Fisseha Itanna, Yuichiro Fujioka, Ausiku Petrus, Morio Iijima, Characteristics of soils under seasonally flooded wetlands (oshanas) in north-central Namibia, African Journal of Agricultural Research, 10.5897/AJAR2016.11758, 11, 46, 4786-4795, 2016.09, Lowland wetlands generally have a high agricultural production potential and can be local hot-spots for
biodiversity. Specific seasonal wetland system is largely distributed in north-central Namibia. Seasonal
wetlands consist of seasonal river wetlands (locally known as oshanas). However, studies on soil
fertility, salinity and sodicity in seasonal river wetlands are still limited in this area. The objective of this
study was hence to investigate the soil fertility status of seasonal wetlands and evaluate their potential
for agricultural production and consider sustainability of the land use system. Soil samples were
collected from 102 different spots of the flood plain within 3 major seasonal rivers, and analyzed for
their physico-chemical properties and salinity and sodicity. The findings for average soil organic carbon
(1.94 g kg-1) and average clay contents (102.3 g kg-1) of seasonal rivers were drastically lower than the
wetland of semi-arid Africa regions (organic carbon, 5.8 g kg-1; clay contents, 340 g kg-1), and organic
carbon and clay content significantly (p<0.05) decreased at the lower part of each seasonal river. Most
of the seasonal river soil’s’ electrical conductivity of saturated paste extract (ECe) and the sodium
adsorption ratio of the saturated paste extract (SAR) were more than 4 dS m-1 and 13, respectively.
However, there were large differences in electrical conductivity of saturated paste extract (ECe) and the
sodium adsorption ratio of the saturated paste extract (SAR) values among the sampling spots. These
findings suggest the high agricultural importance to improve the soil organic matter and clay contents,
and land selection to avoid the strongly high saline-sodic soil sites in seasonal river. .
8. Yoshiaki Nishikawa, Ottilie Shivolo, Martin Angula, Benisiu Thomas, Martha Hangula, Tula Maharero, Yuichiro Fujioka, Village monograph of an agro-pastoral society in north-central Namibia, Journal of Ryukoku Economics, 56, 1, 13-29, 2016.09.
9. Simon K. Awala, Koji Yamane, Yasuhiro Izumi, Yuichiro Fujioka, Yoshinori Watanabe, Kaede C. Wada, Yoshimasa Kawato, Osmund D. Mwandemele, Morio Iijima, Field evaluation of mixed-seedlings with rice to alleviate flood stress for semi-arid cereals, European Journal of Agronomy, 10.1016/j.eja.2016.07.003, 80, 105-112, 2016.07, Flash floods, erratically striking semi-arid regions, often cause field flooding and soil anoxia, resulting in crop losses on food staples, typically pearl millet (Pennisetum glaucum L.) and sorghum (Sorghum bicolor (L.) Moench). Recent glasshouse studies have indicated that rice (Oryza spp.) can enhance flood stress tolerance of co-growing dryland cereals by modifying their rhizosphere microenvironments via the oxygen released from its roots into the aqueous rhizosphere. We tested whether this phenomenon would be expressed under field flood conditions. The effects of mix-planting of pearl millet and sorghum with rice on their survival, growth and grain yields were evaluated under controlled field flooding in semi-arid Namibia during 2014/2015–2015/2016. Single-stand and mixed plant treatments were subjected to 11–22 day flood stress at the vegetative growth stage. Mixed planting increased plant survival rates in both pearl millet and sorghum. Grain yields of pearl millet and sorghum were reduced by flooding, in both the single-stand and mixed plant treatments, relative to the non-flooded upland yields, but the reduction was lower in the mixed plant treatments. In contrast, flooding increased rice yields. Both pearl millet–rice and sorghum–rice mixtures demonstrated higher land equivalent ratios, indicating a mixed planting advantage under flood conditions. These results indicate that mix-planting pearl millet and sorghum with rice could alleviate flood stress on dryland cereals. The results also suggest that with this cropping technique, rice could compensate for the dryland cereal yield losses due to field flooding..
10. Morio Iijima, Simon K. Awala, Yoshinori Watanabe, Yoshimasa Kawato, Yuichiro Fujioka, Koji Yamane, Kaede C. Wada, Mixed cropping has the potential to enhance flood tolerance of drought-adapted grain crops, Journal of Plant Physiology, 10.1016/j.jplph.2016.01.004, 192, 21-25, 2016.01, Recently, the occurrences of extreme flooding and drought, often in the same areas, have increased due to climate change. Wetland plant species are known to oxygenate their rhizospheres by releasing oxygen (O2) from their roots. We tested the hypothesis that wetland species could help upland species under flood conditions; that is, O2 released from the wetland crop roots would ameliorate rhizosphere O2-deficient stress and hence facilitate upland crop root function. Flooding tolerance of upland-adapted staple crops—pearl millet (Pennisetum glaucum) and sorghum (Sorghum bicolor) mix-cropped with rice (Oryza spp.) was investigated in glasshouse and laboratory. We found a phenomenon that strengthens the flood tolerance of upland crops when two species—one wetland and one drought tolerant—were grown using the mixed cropping technique that results in close tangling of their root systems. This technique improved the photosynthetic and transpiration rates of upland crops subjected to flood stress (O2-deficient nutrient culture). Shoot relative growth rates during the flooding period (24 days) tended to be higher under mixed cropping compared with single cropping. Radial oxygen loss from the wetland crop roots might be contributed to the phenomenon observed. Mixed cropping of wet and dryland crops is a new concept that has the potential to overcome flood stress under variable environmental conditions..
11. Yuichiro Fujioka, Rural entrepreneurs and social connections: The management of cattle posts and interactions among farmers in north-central Namibia, MILA Special Issue on Exploring African Potentials: The Dynamics of Action, Living Strategy and Social Order in Southern Africa, 12, 25-38, 2014.03.
12. Yuichiro Fujioka, Vegetation changes and use of palms as a building material by Ovambo agro-pastoralists in North-Central Namibia., African Study Monographs, Supplementary Issue, 10.14989/68458, 30, 89-105, 2005.03.
13. Yuichiro Fujioka, Changes in natural resource use among Owambo agro-pastoralists of north-central Namibia resulting from the enclosure of local frontiers, African Study Monographs Supplementary Issue, 10.14989/96292, 40, 129-154, 2010.03.