Thesis (M.Sc. Agriculture (Soil Science)) -- University of Limpopo, 2021 / Woody plant encroachment results in the degradation of grasslands. It is defined here
as the increase in density, cover and biomass of woody plants into formerly open
grasslands, reducing grassland productivity. Globally, many arid and semi-arid
savanna grasslands are affected by this land cover transformation which changes the
vegetation structure by altering the ratio of woody plants relative to grass species and
influences soil hydrology. In the existing literature there is limited information on the
effects of woody plant encroachment on soil physical and hydrological properties,
especially in savanna grasslands. This study quantified and compared the soil physical
and hydrological properties in the topsoil and subsoil of open and woody plant
encroached grassland sites located on two contrasting soil forms, namely Bainsvlei
and Rensburg. To achieve this objective, the two soils were sampled at various depth
intervals from dug soil profiles at both sites at Towoomba Research Station in Bela Bela, Limpopo Province, South Africa. Soil physical properties including bulk density,
porosity and aggregate stability as well as hydrological properties (water retention and
hydraulic conductivity) were determined from collected samples. Compared to open
grassland, soil bulk density was 11% and 10% greater in the topsoil and subsoil, while
porosity was respectively 6% and 9% lower in the topsoil and subsoil of woody plant
encroached grassland for Rensburg soils. In Bainsvlei soil, there was a minimal
increase and decrease in the soil bulk density and porosity, respectively. Soil
aggregate stability increased by 38% in the subsoil of woody plant encroached
grasslands in Rensburg soil, due to increasing clay content with depth. In Bainsvlei
soil, the soil aggregate stability was 9% and 13% lower in the topsoil and subsoil of
the woody plant encroached grasslands compared to open grassland. Furthermore,
the results revealed that in both soils, there was lower soil water retention and
hydraulic conductivity in the topsoil and subsoil layers of woody plant encroached
grassland than in open grasslands. There were no significant differences observed for
soil hydraulic conductivity in the Bainsvlei and Rensburg topsoil. The subsoil hydraulic
conductivity decreased by 24% in Bainsvlei and 44% in Rensburg soils in the woody
plant encroached grassland. The soil water retention (SWR) decreased with an
increase in woody plants. Specifically, there was 25% and 42% decrease in SWR with
woody plant encroachment in the topsoil and subsoil of Bainsvlei soil, respectively.
The same trend was observed in the Rensburg soils with 50% and 19% decrease in SWR in the topsoil and subsoil, respectively. Overall, the results revealed that soil type
and depth influenced soil physical and hydrological properties in the studied woody
plant encroached savanna grassland. As such, interventions aimed at controlling
woody plant encroachment need to factor in soil type and depth in the development of
management practices tailored to improve the soil hydrology of savanna grasslands
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:ul/oai:ulspace.ul.ac.za:10386/3480 |
| Date | January 2021 |
| Creators | Mashapa, Rebone Euthine |
| Contributors | Dlamini, P.E., Mthimkhulu, S. S. |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | xi, 57 leaves |
| Relation |
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