Thesis (MScAgric (Soil Science)--University of Stellenbosch, 2009. / ENGLISH ABSTRACT: A number of chemical and physical features of Namibian soils in a 22 790 km2, two degree-square block
between 17 – 19 oE and 22 – 23 oS in eastern central Namibia, had been investigated, and the fertility
status established.
In 80 % of samples the nitrate, nitrite, and sulfate concentrations of the saturated paste extract are 0 – 54.6
mg l-1 NO3
-, 0 – 24.7 mg l-1 NO2
-, and 5.4 – 20.9 mg l-1 SO4
2- respectively. In 90 % of samples the plantavailable
phosphorus is below 12 mg kg-1, which is low for a soil under natural grassland, but in line with the
prevailing semi-arid climate and low biomass production of the study area. In 80 % of samples the
extractable calcium, magnesium, potassium, and sodium concentrations are 0.61 – 5.73 cmolckg-1 Ca (122 –
1 146 mg kg-1 Ca), 0.12 – 2.28 cmolckg-1 Mg (15 – 278 mg kg-1 Mg), 0.13 – 0.54 cmolckg-1 K (51 – 213 mg
kg-1 K) and 0.05 – 0.38 cmolckg-1 Na (11 – 87 mg kg-1 Na) respectively, while the exchangeable calcium,
magnesium, potassium, and sodium concentrations are 0.21 – 6.02 cmolckg-1 Ca, 0.12 – 2.01 cmolckg-1 Mg,
0.12 – 0.49 cmolckg-1 K and 0 – 0.13 cmolckg-1 Na respectively. The mean ± 1 standard deviation is 3.57 ±
3.57 cmolckg-1 for cation exchange capacity, 3.48 ± 3.61 for sum of exchangeable bases and 4.53 ± 4.39 for
sum of extractable bases. The cation exchange capacity and the sum of exchangeable bases are virtually
identical, which indicate the almost complete absence of exchangeable H+ and Al3+ in the soils of the study
area, as expected from a semi-arid climate. None of the profiles were classified as saline or sodic. In 80 % of
samples the plant-available iron, manganese, zinc and copper concentrations are 7.2 – 32.8 mg kg-1 Fe, 13.6
– 207.5 mg kg-1 Mn, 0 – 1.80 mg kg-1 Zn and 0 – 4.0 mg kg-1 Cu respectively. Soil organic matter content of
the study area soils ranges between 0.05 – 2.00 %, with most (80 % of samples) containing 0.25 – 1.20 %
organic matter. This is considerably lower than values reported in literature, even for other southern African
countries. The reason lies with the hot, semi-arid climate. The pH distribution is close to normal, with 80 % of
samples having pH (H2O) of 5.54 – 8.18, namely moderately acid to moderately alkaline. Sand, silt and clay
content of most (80 %) samples varies between 60.3 – 89.7 % sand, 4.6 – 25.2 % silt and 3.5 – 19.1 % clay.
The soils of the study area are mainly sandy, sandy loam and loamy sand. In 80 % of samples the coarse
sand fraction ranges from 3.5 – 34.5 %, the medium sand fraction from 20.5 – 37.3 %, the fine sand fraction
from 38.7 – 54.5 % and the very fine sand fraction from 0.0 – 12.9 % of all sand. The fine sand fraction, thus,
dominates, with very fine sand being least abundant. The topsoil contains relatively more coarse sand and
less very fine sand than the subsoil. Instances of sealing, crusting and hardening occur sporadically in the
study area. Cracking is only found in pans, while self-mulching is not evident. No highly instable soils were
encountered in the study area. The water-holding capacity is generally low, with depth limitations in the
western highlands, the Khomas Hochland, and texture limitations in the eastern Kalahari sands. The central
area has soils with a somewhat better water-holding capacity, but it is still very low when compared to arable
soils of temperate, sub-humid and humid zones elsewhere in southern Africa.
Soil characteristics are perceptibly correlated with climate, parent material, topography, degree of dissection
of the landscape and position in the landscape. The most obvious differences are between soils formed in
schistose parent material of the Khomas Hochland in the west and those of the Kalahari sands in the east.
The soils of the study area are unsuitable to marginally suitable for rainfed crop production, due to low
iv
fertility. The study area is climatologically unsuited for rainfed crop production, so the present major land use
is extensive livestock production on large farms. The natural vegetation is well adapted to the prevailing
conditions.
The methodology followed to delineate terrain units, with a combination of procedures involving digital
elevation data and satellite imagery, seems to work well in the Namibian landscape. This study thus served
as a successful proof-of-concept for the methodology, which can in future be rolled out for the remainder of
the country. The site and analytical information is available in digital format as spreadsheets and in a
geographical information system, as well as in a variety of digital and printed maps. / AFRIKAANSE OPSOMMING: ‘n Aantal chemiese en fisiese eienskappe van Namibiese gronde in ‘n 22 790 km2, 1o x 2o blok tussen 17 –
19 o Oos en 22– 23 o Suid in oostelike sentraal-Namibië is ondersoek en die grondvrugbaarheidstatus
bepaal.
In 80 % van monsters is die nitraat-, nitriet- en sulfaatkonsentrasies van die versadigde pasta ekstrak 0.0 –
54.6 mg l-1 NO3
-, 0.0 – 24.7 mg l-1 NO2
-, en 5.4 – 20.9 mg l-1 SO4
2-onderskeidelik. In 90 % van monsters is die
plant-beskikbare fosfor minder as 12 mg kg-1, wat laag is vir gronde onder natuurlike grasveld, maar dit is
verklaarbaar deur die heersende semi-ariede klimaat en lae biomassa produksie in die studiegebied. In 80 %
van monsters is die konsentrasies van ekstraheerbare kalsium, magnesium, kalium en natrium 0.61 – 5.73
cmolckg-1 Ca (122 – 1 146 mg kg-1 Ca), 0.12 – 2.28 cmolckg-1 Mg (15 – 278 mg kg-1 Mg), 0.13 – 0.54 cmolc
kg-1 K (51 – 213 mg kg-1 K) en 0.05 – 0.38 cmolckg-1 Na (11 – 87 mg kg-1 Na) onderskeidelik, terwyl die
uitruilbare kalsium, magnesium, kalium en natrium konsentrasies onderskeidelik 0.21 – 6.02 cmolckg-1 Ca,
0.12 – 2.01 cmolckg-1 Mg, 0.12 – 0.49 cmolckg-1 K and 0.0 – 0.13 cmolckg-1 Na is. Die gemiddelde ± 1
standaardafwyking is 3.57 ± 3.57 cmolckg-1 vir katioonuitruilvermoë, 3.48 ± 3.61 vir die som van uitruilbare
basisse en 4.53 ± 4.39 vir die som van ekstraheerbare basisse. Die katioonuitruilvermoë en som van
uitruilbare basisse is feitlik identies, wat ‘n feitlik algehele afwesigheid van uitruilbare H+ and Al3+ in die
gronde van die studiegebied aandui, soos verwag word weens die semi-ariede klimaat. Geeneen van die
profiele is geklassifiseer as soutbrak of natriumbrak nie. In 80 % van monsters is die plant-beskikbare yster,
mangaan, sink en koper konsentrasies onderskeidelik 7.2 – 32.8 mg kg-1 Fe, 13.6 – 207.5 mg kg-1 Mn, 0.0 –
1.80 mg kg-1 Zn en 0.0 – 4.0 mg kg-1 Cu. Grond organiese material inhoud in die studiegebied wissel tussen
0.05 – 2.00 %, met 80 % van monsters wat 0.25 – 1.20 % organiese material bevat. Dit is aansienlik laer as
die waardes gevind in literatuur, selfs vir ander Suider-Afrikaanse lande. Die oorsaak is die warm, semiariede
klimaat. Die pH verspreiding is feitlik normaal, met 80 % van monsters wat pH (H2O) van 5.54 – 8.18
het, met ander woorde matig suur tot matig alkalies. Sand, slik en klei inhoud van die meeste (80 %)
monsters varieer tussen 60.3 – 89.7 % sand, 4.6 – 25.2 % slik en 3.5 – 19.1 % klei. Die gronde van die
studiegebied is hoofsaaklik sand, sand-leem en leem-sand. In 80 % van monsters beslaan die growwe
sandfraksie 3.5 – 34.5 %, die medium sandfraksie 20.5 – 37.3 %, die fyn sandfraksie 38.7 – 54.5 % en die
baie fyn sandfraksie 0.0 – 12.9 % van die totale sandfraksie. Die fyn sandfraksie is dus dominant, terwyl die
baie fyn sandfraksie die skaarsste is. Die bogronde bevat relatief meer growwe sand en minder baie fyn
sand as die ondergronde. Gevalle van verseëling, korsvorming en verharding kom sporadies in die
studiegebied voor. Krake kom net in panne voor en self-omkering is nie opgemerk nie. Geen hoogsonstabiele
gronde is in die studiegebied gevind nie. Die waterhouvermoë is in die algemeen laag, met
dieptebeperkinge in die westelike hooglande, die Khomas Hochland, en tekstuurbeperkinge in die oostelike
Kalahari sande. Die sentrale gedeelte het gronde met ‘n ietwat beter waterhouvermoë, maar dis steeds baie
laag in vergelyking met akkerbougronde van gematigde, sub-humiede en humiede sones elders in Suider-
Afrika.
Grondeienskappe is ooglopend verwant aan klimaat, moedermateriale, topografie, graad van gebrokenheid
van die landskap en posisie in die landskap. Die duidelikste verskille kom voor in die gronde wat van
vi
skisagtige moedermateriaal van die Khomas Hochland in die weste en dié wat in die Kalahari sande in die
ooste gevorm het. Die gronde van die studiegebied is ongeskik tot marginaal geskik vir droëland akkerbou,
weens die lae vrugbaarheid. Aangesien die studiegebied klimatologies ongeskik is vir droëland akkerbou, is
die huidige hoof landgebruik ekstensiewe veeproduksie op groot plase. Die natuurlike plantegroei is goed by
die heersende omstandighede aangepas.
Die metodiek wat gevolg is om terreineenhede af te baken, wat ‘n kombinasie van prosedures met digitale
hoogtedata en satellietbeelde is, blyk goed te werk vir die Namibiese landskap. Hierdie studie dien dus as ‘n
suksesvolle bewys-van-konsep van die metodiek, wat in die toekoms uitgebrei kan word na die res van die
land. Die veld- en ontledingsinligting is beskikbaar in digitale formaat, in ‘n geografiese inligtingstelsel en ‘n
verskeidenheid digitale- en gedrukte kaarte.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/4068 |
| Date | 03 1900 |
| Creators | Coetzee, Marina Elda |
| Contributors | Ellis, F., University of Stellenbosch. Faculty of Agrisciences. Dept. of Soil Science. |
| Publisher | Stellenbosch : University of Stellenbosch |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | Various pagings : ill., maps. |
| Rights | University of Stellenbosch |
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