Thesis (MScFor)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: A field trial of six replications was established to test the effect of various wood ash and fertilisers application rates on soil chemistry, tree nutrition and early growth rate of a clonal Eucalyptus grandis x urophylla stand. Wood ash from pulpmills is currently disposed of in landfills. Increasing costs and potential environmental risks have driven companies to investigate alternative disposal methods. Ash consists of a combination of carbonates, hydroxides and other calcium containing minerals that induce the liming effect if ash is applied to a soil. The trial was established near Richards Bay in October 2013 on a sandy soil with a low buffer capacity and a pH of approximately 5.5. The trial consists of four wood ash application rates in combination with three levels of fertiliser, viz. no fertiliser, 150 g conventional NPK fertiliser mixture, or 320g NPK controlled release mixture. Fertiliser mixtures and application levels were based on previous fertiliser trials in the region. Ash application rates for the field trial were based on a lab incubation study done with soil samples from Richards Bay, to which increasing amounts of lime were added. The study tested wood ash application rates of 0, 300, 600 and 1200 kg/ha. Field measurements were taken at 4 and 8 months after trial establishment. The primary objective was to investigate which application levels in combination with the type of fertiliser could be applied to soils without negatively affecting the stand nutrition or increase the levels of potentially harmful elements in the soil; thus investigating the feasibility of safely disposing wood ash on plantation soils as an alternative disposal method. Soil nutrient concentrations were not affected by individual wood ash treatments, but more a product of the time interval after the ash additions were made. Soil C, P, K+ and Mg2+ showed decreased concentrations from 4-8 months after establishment. Ca2+ concentrations increased in the same time interval. In addition, Na+ and B concentrations decreased from 4-8 months. Soil heavy metal concentrations for Cd, Hg, Cr and Pb, analysed for 0-1200 kg/ha ash rates, were well below toxic levels at both time intervals. Wood ash induced a temporary liming effect. Mean soil pH increased with 0.6 units for the period 0 - 4 months and decreased with 0.4 units at 4 - 8 months after trial establishment. Foliar nutrient analyses and assessment techniques revealed sub-optimal nutrient concentrations for P, K and Zn at 4 and 8 months of age. Concentrations were defined as sub-optimal, as none of the nutrients were below critical levels. Foliar heavy metal concentrations for Cd, Hg, Cr and Pb, measured at both time intervals, were less than 1mg/kg. The small concentrations found in this project were attributed to the low bioavailability of all four elements and were likely a product of the edaphic factors at Richards Bay, which was representative of a large greater portion of the Zululand coastal plain sites. The response in biomass index ranged between 13 % and 683 % relative to the control treatment (A0F0). Results showed that application of purely wood ash, or in combination with a supplementary N and P source increased growth up to 8 months after trial establishment for wood ash applications up to 1200 kg/ha. This project demonstrated that 1200 kg/ha wood ash can safely be disposed of on a typical Zululand coastal sand with little environmental risk and no supressed growth, provided that it is balanced with an appropriate NP fertiliser. / AFRIKAANSE OPSOMMING: ‘n Veldproef met ses herhalings is in Oktober 2013 uitgelê met die doel om die uitwerking van verskillende vlakke hout as en kunsmis toedienings op die grond-voedingstof status, boom-voedingstof status en die groei-tempo van ‘n Eucalyptus grandis x urophylla hibried plantasie te bestudeer. Hout as by pulpmeulens word tans weggegooi op stortingsterreine. Toenemende onkostes vir storting en die omgewingsrisiko’s gebonde aan stortingsterreine, dryf maatskappye om verbeterde en meer omgewingsvriendelike metodes te ondersoek om van die as ontslae te raak. Hout as bestaan uit ‘n reeks karbonate, hidroksiede en kalsium bevattende minerale en is verantwoordelik vir die bekalkingseffek op die grond na toediening. Die veldproef is geleë naby Richardsbaai op ‘n sanderige grond met n lae bufferkapasiteit en pH van ongeveer 5.5. Die proef het vier hout as vlakke getoets, gekombineer met drie vlakke van bemesting: geen, 150g konvensionele landbou kunsmis (CV) óf 320g beheerd-vrystellende kunmis (CRF). Die kunsmismengsels en vlakke van bemesting is gebaseer op bestaande of voltooide bemestingseksperimente in die streek. Hout as vlakke was bereken in gekontroleerde laboratorium toestande en gebaseer op ‘n inkubasie studie met grond monsters verkry vanaf Richardsbaai, waarby toenemende vlakke suiwer landboukalk gevoeg is. Die veldproef het hout as vlakke van 0, 300, 600 en 1200 kg/ha getoets. Veld metings is op 4 en 8 maande na behandeling geneem. Die primêre doelwit van die studie was om te bepaal watter vlak hout as en kunmis kombinasie toegedien kan word, sonder om die grond-voedingstof status negatief te beïnvloed of ‘n potensiële skadelike uitwerking op die plantasie groei te veroorsaak. Die uiteinde van die studie was om die haalbaarheid van hout as toedienings op plantasie gronde te bestudeer relatief tot die huidige praktyk van storting, insluitend die risiko van moontlike skadelike newe-effekte. Grondvoedingstatus was nie beduidend beïnvloed deur individuele hout as toevoegings nie, maar was eerder ‘n funksie van die tydsduur sedert behandeling. Grond koolstof, P anione, K+ en Mg2+ konsentrasies het beduidend afgeneem in die periode van 4 - 8 maande na behandling. Die Ca2+ konsentrasies het toegeneem tussen 4 en 8 maande en terselfdertyd het Na+ en B konsentrasies afgeneem. Die swaarmetaal status, spesifiek vir Cd, Hg, Cr en Pb, vir toevoegings van 0-1200 kg/ha hout as was beduidend laer as toelaatbare vlakke in gronde op albei tydsintervalle. Die hout as het ‘n tydelike toename in grond pH veroorsaak. Die gemiddelde pH het tussen 0 - 4 maande toegeneem met 0.6 eenhede en gedurende 4 - 8 maande afgeem met 0.4 eenhede. Blaarontledings en voedingstof assesseringsmetodes het sub-optimale konsentrasies vir P, K en Zn getoon op die ouderdom van 4 en 8 maande. Voedingstof konsentrasies is as sub-optimaal geklassifiseer, omdat konsentrasies nooit laer as kritieke waardes vir gebreksimptome was nie. Die inhoud van Cd, Hg, Cr en Pb in blare was aansienlik kleiner as 1 mg/kg op albei tydsintervalle. Die merkwaardige lae konsentrasies wat in die projek aangeteken is, word toegekryf aan die lae bio-beskikbaarheid van al vier elemente as gevolg van die edafiese faktore eie aan die Richardsbaai omgewing (en ook aan groot dele van die Zoeloelandse kusvlakte). Die groeireaksie (bepaal as biomassa indeks op ouderdom 8 maande) het gewissel van 13 % - 683 % groter as die kontrole behandeling (A0F0). Resultate het bewys dat toedienings van suiwer hout as, of hout as gekombineer met ‘n addisionele N en P kunsmisbron die groei postief beïnvloed tot op die ouderdom van 8 maande. Die studie het bewys dat 1200 kg/ha hout as veilig toegedien kan word op die sandgronde van die kusgebiede in Zululand, met minimale omgewingsrisiko en geen tekens onderdrukte groei nie, mits dit gebalanseer word met ‘n geskikte NP kunsmisbron.

Thesis (MSc)--Stellenbosch University, 2004. / ENGLISH ABSTRACT: Bush encroachment in savannas leads to reduced diversity, productivity and profitability of rangelands. This holds important implications for the livestock and eco-tourism industries, as well as for subsistence ranchers in the South African semi-arid savannas, who depend on this vegetation type for economic and livelihood purposes. Soil moisture, nutrients, rue and herbivory are generally regarded as the principal factors determining vegetation structure and function within savannas. The factors and processes involved in the determination of the tree:grass ratio within savannas are, however, not clearly understood. We investigated the role of soil type and management strategy (cattle, game and communal grazing) in the determination of the presence and distribution of plant species in general, and on the presence and distribution of the encroaching tree species, Acacia mellifera, specifically. Both shortand long-term trends were investigated. The study area, the Kimberley Triangle, (Northern Cape Province, South Africa), was ideal for this kind of study because it has different management strategies practised on several soil types, and bush encroachment is a widespread phenomenon. Contrary to the belief that heavy livestock grazing is the main cause of increases in the tree:grass ratio, we found that soil type, through its effects on plant growth and on the presence and availability of soil moisture and nutrients, is more important in determining vegetation composition than management strategy. It was found that the various types of grazing management mainly influenced vegetation structure and function by affecting the competitive interactions between Ns-fixing woody species and non-Ns-fixing grasses. Of the soil factors affecting vegetation composition, soil texture was a good indicator of the physical conditions for plant growth in an area, and also of the presence and availability of soil moisture and nutrients. We found that sand and clay soils are relatively resistant to bush encroachment as compared to loamy-sand and -clay mixes. This is because woody growth is impaired in the first-mentioned habitats by soil texture, soil moisture regimes and heavy utilisation. In soils with combinations of loam, sand and clay, soil texture and moisture are not limiting to woody growth and if the repressive competitive effect of grasses on woody vegetation is removed, opportunities are created for recruitment of woody species and encroachment. Additionally, rockiness increases soil moisture infiltration. In the study area, woody species, and specifically A. mellifera, are associated with these areas. We suggest that in the study area, rocky areas are naturally encroached. This is in agreement with the patchdynamic approach to savanna vegetation dynamics. Because soil moisture is such an important factor in the determination of the tree:grass ratio in the study area, we further suggest that in above-average rainfall years, when soil moisture conditions are optimal for woody seed germination, establishment and growth, heavy grazing should be avoided, as it would provide the opportunity for encroachment. Keywords: Bush encroachment; N2-fixing species; game, cattle, communal grazing; soil texture; soil moisture; soil nutrients; Acacia mellifera; tree-grass competition. / AFRIKAANSE OPSOMMING: Bosindringing in savanna gebiede het verlaagde diversiteit, produktiwiteit en winsgewendheid van natuurlike weivelde tot gevolg. Behalwe dat dit die Suid-Afrikaanse vee- en ekotoerisme bedrywe raak, is verskeie bestaansboerderye afhanklik van die plantegroei-tipe vir oorlewing. Grondvog, grondvoedingstowwe, vuur en beweiding word algemeen aanvaar as die belangrikste faktore wat die struktuur en funksie van savannas bepaal. Daar is egter nog nie duidelikheid oor die prosesse wat betrokke is in die bepaling van die boom-gras verhouding in savannas nie. In dié studie het ons ondersoek ingestel na die invloed van grond tipe en beweidingstrategieë (beweiding deur beeste, wild, of kommunale beweiding) op die algemene verspreiding van verskillende plant spesies, en ook op die van die indringer spesie, Acacia mellifera. Beide kort- en lang-termyn patrone is ondersoek. Die studiegebied, die Kimberley Driehoek in die Noord-Kaap, Suid-Afrika, was ideaal vir so 'n ondersoek omdat verskillende beweiding strategieë op verskeie grond-tipes beoefen word maar bosindringing steeds 'n algemene verskynsel in die gebied is. Ons bevinding was dat, ten spyte van die feit dat daar oor die algemeen geglo word dat swaar beweiding die hoof oorsaak van bosindringing is, grond-tipe belangriker is in die bepaling van die spesie-samestelling van 'n gebied. Dit is as gevolg van die feit dat grond-tipe die groei van plante beïnvloed deur die teenwoordigheid en beskikbaarheid van grondvog en -nutriënte te bepaal. Die verskillende beweidingstrategieë beïnvloed meerendeels die kompetatiewe interaksies tussen N2-bindende hout-agtige spesies teenoor nie-Nj-bindende gras-agtige spesies. Grond-tekstuur was 'n goeie aanduiding van die algemene toestande vir plantegroei en ook van die teenwoordigheid en beskikbaarheid van grondvog en -nutriënte. Ons het bevind dat sand en klei grond, relatief tot leem, sand en klei kombinasies, weerstandbiedend is teen bosindringing as gevolg van die tekstuur, water-regimes en swaar beweidings vlakke wat op die grond-tipes voorkom. Omdat grond-tekstuur en grondvog nie beperkend is op die leem-, sand- en klei-grond kombinasies nie, kan bosindringing maklik hier voorkom as die onderdrukkende effek wat grasse op houtagtige plantegroei het, deur swaar beweiding verwyder word. A. mellifera is ook oor die algemeen met klipperige gebiede geassosieer omdat klipperigheid lei tot verhoogde infiltrasie van grondvog. In die studie-gebied is klipperige areas dan ook van nature ingedring deur A. mellifera. Dit stem ooreen met die siening dat savannas bestaan uit "laslappe" van verskillende plantegroei (patch-dynamic approach). Dit was duidelik dat grondvog 'n belangrike bepalende faktor is in die bepaling van die boom-gras verhouding in die studiegebied. Ons stel dus voor dat in bo-gemiddelde reënval jare, swaar beweiding vermy moet word, omdat houtagtige saailinge gedurende die tydperke maklik kan ontkiem en vestig juis omdat grondvog dan nie beperkend is nie. Sleutelwoorde: Bosindringing; N2-bindende spesies; bees, wild, kommunale beweiding; grond tekstuur; grond-vog; grond-nutriënte; Acacia mellifera; boom-gras kompetisie.