The influence of land use on humic substances in three semi-arid agro-ecosystems in the Free State
| dc.contributor.advisor | Du Preez, C. C. | |
| dc.contributor.advisor | Kotze, E. | |
| dc.contributor.author | Akhosi-Setaka, Makuena Cynthia | |
| dc.date.accessioned | 2018-01-24T08:34:36Z | |
| dc.date.available | 2018-01-24T08:34:36Z | |
| dc.date.issued | 2009-05 | |
| dc.description.abstract | English: This study was initiated to complement earlier investigations into soil organic matter degradation and restoration on account of agricultural land use in the Free State Province of South Africa. In these studies no attention was given to the response of humic substances which represent the most active fraction of organic matter. The aim with this study was therefore to quantify the influence of agricultural land use on humic substances in soils of semi-arid regions. Topsoil (0-200 mm) samples from distinctive agro-ecosystems at Harrismith (Mean annual rainfall, MAR = 624 mm and Mean annual temperature, Ta = 13.8°C), Tweespruit (MAR = 544 mm and Ta = 14.8°C) and Kroonstad (MAR = 566 mm and Ta = 16.6°C) were selected for use in this study. An agroecosystem implies a region where the three environmental factors affecting yield, namely climate, slope and soil are for practical purposes homogeneous. The selected samples represent a virgin (grassland soil never cultivated before), cultivated (formerly grassland soil cultivated for at least 20 years) and restored (formerly cultivated soil converted to perennial pasture for at least 15 years) Plinthustalfs (10.6 to 13.5% clay) at every agro-ecosystem. Parameters quantified comprise crude soil, extractable soil, humic acid and fulvic acid C contents, N contents and C/N ratios. Concerning these parameters, cultivated soil was compared with virgin soil and restored soil with cultivated soil. The crude soil C content of the virgin soils varied from 7.3 g C kg-1 soil in the warmer, drier Kroonstad agro-ecosystem to 21.6 g C kg-1 soil in the cooler, wetter Harrismith agro-ecosystem. Across agro-ecosystems the contribution of extractable to crude soil C was almost constant, namely 47.1 to 48.4%. The contribution of humic acid C to extractable soil C decreased and that of fulvic acid C to extractable soil C increased from the Kroonstad to Harrismith agroecosystem. Cultivation reduced crude soil C in the three agro-ecosystems with 50.2 to 51.8%. This is equivalent to absolute losses of 3.8, 8.2 and 10.8 g C kg-1 soil at Kroonstad, Tweespruit and Harrismith agro-ecosystems respectively. Loss of extractable soil C was more variable ranging from 36.7% or 1.3 g C kg-1 soil in the warmer, drier Kroonstad agro-ecosystem to 48.2% or 5.1 g C kg-1 soil in the cooler, wetter Harrismith agro-ecosystem. Trends of this nature were nonexistent for either humic or fulvic acid C losses. Gains of crude soil C ranged from 5.4 g C kg-1 soil in the warmer, drier Kroonstad agro-ecosystem to 8.0 g C kg-1 soil in the cooler, wetter Harrismith agroecosystem. This trend manifested also in extractable soil C gains which were lowest at Kroonstad (1.5 g C kg-1 soil) and highest at Harrismith (2.8 g C kg-1 soil). Neither humic acid C nor fulvic acid C showed trends of this nature. The N contents although more variable than the C contents are to a large extent supportive concerning organic matter in the virgin, cultivated and restored soils of the three agro-ecosystems. Further elaboration on the N contents is therefore not justified here. Based on both C and N indices, it can be stated that humic substances did not show explicit trends on account of land use as was the case with organic matter per se. This phenomenon warrants further investigation since humic substances are regarded as the most reactive fraction of organic matter. | en_ZA |
| dc.description.abstract | Afrikaans: Die studie is geïnisieer om vorige ondersoeke oor die degradasie en restourasie van organiese materiaal weens landboukundige landgebruik in die Vrystaat Provinsie van Suid-Afrika te komplementeer. In hierdie studies is geen aandag aan die reaksie van humiese stowwe, wat die mees reaktiewe fraksie van organiese materiaal verteenwoordig, gegee nie. Die doel met hierdie studie was dus om die invloed van landboukundige landgebruik op humiese stowwe in gronde van halfdroë gebiede te kwantifiseer. Bogrondmonsters (0-200 mm) vanaf onderskeibare agro-ekosisteme by Harrismith (Gemiddelde jaarlikse reënval, GJR = 624 mm en Gemiddelde jaarlikse temperatuur, Tj = 13.8°C), Tweespruit (GJR = 544 mm en Tj = 14.8°C) en Kroonstad (GJR = 566 mm en Tj = 16.6°C) is vir die studie geselekteer. ‘n Agro-ekosisteem impliseer ‘n gebied waar die drie omgewingsfaktore wat opbrengs beïnvloed, naamlik klimaat, helling en grond vir alle praktiese doeleindes homogeen is. Die geselekteerde monsters verteenwoordig ‘n onversteurde (graslandgrond wat nooit voorheen bewerk is), bewerkte (vroeër graslandgrond wat vir ten minste 20 jaar bewerk is) en gerestoureerde (vroeër bewerkte grond wat vir ten minste 15 jaar na aangeplante weiding omgeskakel is) Plinthustalfs (10.6 tot 13.5% klei) by elke agro-ekosisteem. Parameters wat gekwantifiseer is sluit in rugrond, ekstraheerbare grond, humiensuur en fulviensuur C-inhoude, N-inhoude en C/N-verhoudings. Die rugrond C-inhoud van die onversteurde gronde varieer van 7.3 g C kg-1 grond in die warmer, droër Kroonstad agro-ekosisteem tot 21.6 g C kg-1 grond in die koeler, natter Harrismith agro-ekosisteem. Oor agro-ekosisteme was die bydrae van ekstraheerbare tot rugrond C bykans konstant, naamlik 47.1 tot 48.4%. Die bydrae van humiensuur C tot ekstraheerbare grond C het afgeneem en die van fulviensuur C tot ekstraheerbare grond C het toegeneem van die Kroonstad tot Harrismith agro-ekosisteem. Bewerking het die rugrond C in die drie agro-ekosisteme met 50.2 tot 51.8% verlaag. Die is ekwivalent aan absolute verliese van 3.8, 8.2 en 10.8 g C kg-1 grond by Kroonstad, Tweespruit en Harrismith agro-ekosisteme respektiewelik. Verlies van ekstraheerbare grond C was meer varieerbaar en varieer van 36.7% of 1.3 g C kg-1 grond in die warmer, droër Kroonstad agro-ekosisteem tot 48.2% of 5.1 g C kg-1 grond in die koeler, natter Harrismith agro-ekosisteem. Neigings van die aard bestaan nie vir humien- of fulviensuur C verliese nie. Winste van rugrond C varieer van 5.4 g C kg-1 grond in die warmer, droër Kroonstad agro-ekosisteem to 8.0 g C kg-1 grond in die koeler, natter Harrismith agro-ekosisteem. Die neiging het ook in die ekstraheerbare grond C gemanifesteer waar winste die laagste by Kroonstad (1.5 g C kg-1 grond) en hoogste by Harrismith (2.8 g C kg-1 grond) was. Beide humiensuur C en fulviensuur C het geen neigings van die aard getoon nie. Die N-inhoude was, alhoewel meer varieerbaar as die C-inhoud tot ‘n groot mate ondersteunend betreffende organiese materiaal in die onversteurde, bewerkte en gerestoureerde gronde van die drie agro-ekosisteme. Verdere uitbreiding oor die N-inhoude is daarom hier nie geregverdig nie. Gebaseer op beide die C- en N-indekse kan dit gestel word dat humiese stowwe nie sulke duidelike neigings toon weens landgebruik as wat die geval met organiese materiaal was nie. Die verskynsel regverdig verdere navorsing omdat humiese stowwe as die mees reaktiewe fraksie van organiese materiaal beskou word. | af |
| dc.identifier.uri | http://hdl.handle.net/11660/7695 | |
| dc.language.iso | en | en_ZA |
| dc.publisher | University of the Free State | en_ZA |
| dc.rights.holder | University of the Free State | en_ZA |
| dc.subject | Fulvic acid | en_ZA |
| dc.subject | Humic acid | en_ZA |
| dc.subject | Organic carbon | en_ZA |
| dc.subject | Soil organic matter | en_ZA |
| dc.subject | Organic nitrogen | en_ZA |
| dc.subject | Humus | en_ZA |
| dc.subject | Land use -- Envrionmental aspects | en_ZA |
| dc.subject | Soil fertility -- South Africa -- Free State | en_ZA |
| dc.subject | Dissertation (M.Sc. (Soil, Crop and Climate Sciences))--University of the Free State, 2009 | en_ZA |
| dc.title | The influence of land use on humic substances in three semi-arid agro-ecosystems in the Free State | en_ZA |
| dc.type | Dissertation | en_ZA |