Abstract
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. Key words: Soil fertility, seasonal wetland, soil salinity, sodicity, Cuvelai Seasonal Wetland System (CSWS).
Highlights
Semi-arid ecosystems in tropical regions exhibit high climatic variability, where food security is threatened by frequent drought (Steiner and Rockström, 2003)
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 sand, silt, and clay in ondombe were 864, 53 and 83 g kg-1, respectively. These results show that ondombe soils are sandy with little clay contents
Summary
Semi-arid ecosystems in tropical regions exhibit high climatic variability, where food security is threatened by frequent drought (Steiner and Rockström, 2003). In north-central Namibia, during the rainy period, a specific seasonal wetland system is usually experienced, which is commonly referred to as Cuvelai Seasonal Wetland System (CSWS). In the CSWS, 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 (Figure 1). Efficient utilization of oshanas and ondombes during rainy seasons, may alleviate problems associated with drought and food production in Namibia. Ondombes are usually situated on a gentle slope having some vegetation. Closer examination has revealed the prevalence of different soil types at different slope positions
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