Epsilon Archive for Student Projects

Abstract

Farming in Sub-Saharan Africa is expected to be faced with more frequent droughts and storms. Most farming systems lack the infrastructure to cope with such extreme events, and rely on soil water retention and soil hydraulic conductivity to store water while allowing stormwater to infiltrate. However, research on improving soil hydraulic properties in this region has been limited due to scarce funding and resources. Pedotransfer functions (PTFs), which use easily measurable and more often readily available parameters to predict hydraulic characteristics, offer potential solutions, but only limited numbers of PTF have been developed or tested for Sub-Saharan Africa specifically. This study aims to evaluate soil hydraulic properties of agricultural soils using PTFs in Zambia (southern Africa). Twelve existing PTFs were tested on their accuracy to predict field-saturated hydraulic conductivity (Kfs) and water retention. Therefore, 32 fields in 3 districts and 2 farming systems (small-scale and commercial farms) were sampled for soil texture, organic matter, bulk density, water retention and Kfs in top and subsoil.
The results revealed higher and more spatially varying infiltration rates on commercial farms (about twice the rate), while showing signigficantly higher clay content (mean= 40%). A reason might be the formation of cracks and different soil management practices like tillage, impacting soil structure and determining Kfs. Further robust driving factors were difficult to determine. PTFs predicting Kfs were scarce and the ones existing failed to adequately predict Kfs. Obtained agreements of PTF estimated and field measured field capacity (-10kPa) ranged between -0.21 <R<0.41 (top-soil) and -0.71<R<0.40 (sub-soil), while permanent wilting point (-1500kPa) varied within ranges of -0.45<R<0.49 (top-soil) and -0.69<R<0.42 (sub-soil). Notably, permanent wilting points at >0.15 vol% were performing poorly possibly due to lab analysis errors at high pressures. My results highlight the need to go beyond basic soil parameters for determining hydraulic soil properties, and a need to further build soil data from field sampling to improve PTFs applicability for agricultural soils in Zambia.