Abstract
Abstract. Sandy soils with fragipans are usually considered poorly suited for agriculture. However, these soils are cultivated in Namibia as they can secure a minimum harvest during droughts. In order to understand the hydrological influence of fragipans in these soils, Ehenge, their soil moisture content was measured for 4 months. These data were then compared to a deep soil without fragipan, Omutunda, which is more productive during normal years but less productive during droughts. The results illustrate that the combination of sandy topsoil and shallow fragipan has beneficial effects on plant-available water during dry periods. Three reasons can be determined: (i) high infiltration rate in the sandy topsoil, (ii) prevention of deep drainage by the fragipan, and (iii) limitation of evaporation losses through the sand. Consequently, transferring these findings to other dry, sandy areas with fragipans, with respective consequences on farming practices, crop productivity, and food security, should be possible.
Highlights
Droughts or sustained dry periods are a common feature in semi-arid regions of Namibia and can occur more or less every other year (Keyler, 1995)
Maximum ranges of 315 % occurred at a depth of 45 cm, which indicates that the underlying fragipan has a significant influence on soil hydrology, by preventing deep drainage and storing of water above
The measurement period can, be considered a regular year in terms of rainfall. This rainfall amount limits an assessment of moisture dynamics in years of drought, the positive effect of the fragipan in Ehenge on soil hydrology and water availability for plants is clearly visible in the higher relative available soil water (RASW) values in comparison to the reference soil Omutunda
Summary
Droughts or sustained dry periods are a common feature in semi-arid regions of Namibia and can occur more or less every other year (Keyler, 1995) They are often accompanied by significant crop failures and pose a threat to local food security. The impact on the population was strong in the north-central regions, where many people still rely on subsistence crop production Such droughts with all their negative implications will most likely increase in frequency as a result of climate change (IPCC, 2021). In addition to these extreme drought events, plant water availability in north-central Namibia is in general highly variable over the cultivation season and from one year to another (Rockström and De Rouw, 1997). If occurring during the flowering and grain filling period, strongly reduces crop yield (Vadez, 2014; Vereecken et al, 2008), while crops have better capacity to compensate for water shortage during their early growth phases (Rockström and De Rouw, 1997)
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