Yuichiro Fujioka

Mixed cropping has the potential to enhance flood tolerance of drought-adapted grain crops

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.

VEGETATION CHANGES AND USE OF PALMS AS A BUILDING MATERIAL BY OVAMBO AGRO-PASTORALISTS IN NORTH-CENTRAL NAMIBIA

This paper focuses on the mutual transition between vegetation and timber use by the Ovambo people in north-central Namibia and their use of palms for timber in recent years. The vegetation around the research area was characterized as Mopane savanna, dominated by Colophospermum mopane. Historically, the Ovambo used mainly Mopane trunks for timber. However, as bush encroachment advanced in some parts of north-central Namibia, residents were forced to collect Mopane timber from the south. Since the 1970s, however, collecting Mopane has become diffi cult, and the inhabitants have therefore begun to use palm petioles for timber. Because the use of this resource requires many palm petioles, an environment conducive to grow many palms is required to make this option feasible. The vegetation confi guration of this environment was formed mainly by three factors: (1) the unique fl ood terrain initially dispersed palm seeds over a wide area, (2) humans involuntarily dispersed seeds after eating, (3) palms were conserved by the residents. Thus, the increased use of palms emerged at a point of intersection between a change in vegetation patterns and a change in plant use by humans. The critical points of this use are its sustainability and the maintenance of traditional building complexity.

Classification of Small Seasonal Ponds Based on Soil–Water Environments in the Cuvelai Seasonal Wetland System, North-Central Namibia

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.

Variations in Mopane Vegetation and its Use by Local People: Comparison of Four Sites in Northern Namibia

The aim of this study was to clarify variation in mopane (Colophospermum mopane) vegetation in northern Namibia, focusing on the differences and commonalities in vegetation structure and tree uses by local people. Four study sites representing different land units classified by landscape, land use patterns, and its use by different ethnic groups were selected. Vegetation surveys at each site found mopane as the dominant species at all sites, although mopane density ranged from 217.1 to 868.7 individual trees/ha among the sites/land units. There were four types of mopane tree shape by tree height and stem number. The ratios of other tree species to mopane differed much among land units and sites. Interviews with the local people on mopane utilization found that they were highly dependent on trees as a resource for fuel and building material, and commonly used mopane at all sites. Although the mopane utilization was similar among all four sites, the non-mopane tree utilization depended on the characteristics of the tree species composition at specific sites. Mopane vegetation was naturally characterised by the dominance of mopane, but the sites were heterogeneous in species composition, mopane tree shape, and its use by local people, which were mutually interrelated.