The effects of forest residue management on topsoil nutrient dynamics, and on early growth responses of Eucalyptus grandis x urophylla under varied levels of fertilization

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dc.contributor.advisorDu Toit, Benen_ZA
dc.contributor.advisorHardie-Pieters, Ailsa G.en_ZA
dc.contributor.authorNieto Lawrence, Juan Sebastianen_ZA
dc.contributor.otherStellenbosch University. Faculty of AgriSciences. Dept. of Forest and Wood Science.en_ZA
dc.date.accessioned2022-03-10T13:16:31Zen_ZA
dc.date.accessioned2022-04-29T12:53:19Zen_ZA
dc.date.available2022-12-24T03:00:10Zen_ZA
dc.date.issued2022-03en_ZA
dc.descriptionThesis (MSc) -- Stellenbosch University, 2022.en_ZA
dc.description.abstractENGLISH ABSTRACT: The sheer mass of forest residues, or slash left behind after harvest hampers site accessibility and poses a significant fire hazard. A low intensity burn is normally sufficient to reduce the fuel load, but other methods of management that retain residues may be more sustainable practices regarding soil nutrient capital. In this study, different methods of slash management were investigated on two sites in KwaZulu-Natal, measuring early effects on growth of Eucalyptus spp. and soil nutrient dynamics. These slash management practices included residue retention (R; control), mulching (M), burning (B), and burn-and-disking (DB). Applied in factorial to these were four levels of fertilization: a low dose of N-rich fertilizer (LowN), a high dose of N-rich fertilizer (HighN), a low dose of P-rich fertilizer (HighP), and an unfertilized control (O). On the first site, in Zululand, KwaMbonambi, E. grandis x urophylla was planted on deep sands, and large responses to slash management were measured within a year of planting. The B and DB treatments resulted in less acidic soil pH values, and a pulse of plant available P, Ca2+, and Mg2+, with no detectable effect on soil mineral N.This pulse caused young eucalypts planted on B and DB treatments to growsignificantly taller and wider than those on M and R treatments, being between 0.4 m and 0.7 m taller at six months after planting, and between 1.5 cm and 2.0 cm wider at breast height by eleven months after planting. Growth on DB treatments was significantly greater than even that on B treatments, with no response to fertilization on either treatment. Eucalypts on M and R treatments, however, displayed a sensitivity to fertilizer treatments, with growth improved most by HighP fertilization and least by the unfertilized control. This highlighted an interaction between residue management and fertilization. The M treatment, specifically, resulted in the greatest response to fertilization, the poorest overall growth of eucalypts, and an early locking-up of soil N expressed as soil C/N ratios greater than 30, and net immobilization after aerobic incubation of soil samples. The R treatment produced marginally better growth than the M treatment, as well as an early pulse of N mineralization that had disappeared within six months. Interestingly, the mineralization potential of soils from all treatments decreased steadily over time, showing net mineralization initially, but net immobilization by the end of the study period. This indicated a decreasing substrate quality over time. On the second site, in the Midlands, Hilton, E. grandis x nitens was planted on humic topsoils with apedal subsoils. Similar responses to the B and DB treatments were expressed in the soil within half a year of planting, but a pulse of NH4+was also found to be associated with these treatments. The M and R treatments, conversely, resulted in a pulse of NO3−, expressed most significantly five months afterplanting. These results highlighted short-term site-specific responses to residue management, as well as early influences of two relatively new methods of slash management: mulching, and disking after a burn.en_ZA
dc.description.abstractAFRIKAANS OPSOMMING: Die blote massa van tak-afval en ander oesreste wat na kaalkap in plantasies agtergelaat word, belemmer toeganklikheid vir nuwe aanplantings en hou 'n aansienlike brandgevaar in. 'n Lae intensiteit, beheerde brand is normaalweg voldoende om hierdie brandstoflading te verminder, maar ander bestuursmetodes wat oesreste behou, is gewoonlik meer volhoubaar met betrekking tot grondvoedingstof kapitaal. In hierdie studie is verskillende bestuursmetodes van oesreste op twee terreine in KwaZulu-Natal ondersoek, met fokus op grondvoedingstof dinamika asook die aanvanklike groeireaksie van Eucalyptus spesies. Die oesreste behandelings het ingesluit: retensie van tak-afval (R, kontrole behandeling), versnippering van reste tot ʼn deklaag (M), beheerde brand (B) asook brand gevolg deur in-egting met ʼn skotteleg (DB). In ’n faktoriaal ontwerp hiermee saam is vier vlakke van bemesting toegedien: 'n lae dosis N-ryke kunsmis (LowN), 'n hoë dosis N-ryke kunsmis (HighN), 'n lae dosis P-ryke kunsmis (HighP), en nul bemesting (O). Op die eerste perseel, in Zoeloeland,KwaMbonambi, is E. grandis x urophylla op diep sandgrond geplant, en ʼn sterk reaksie op oesreste bestuur is binne 'n jaar na aanplanting gemeet. Die B- en DB-behandelings het gelei tot 'n puls van plantbeskikbare P, Ca2+ en Mg2+, asook hoër pH-waardes, met geen beduidende effek op grond minerale N vlakke nie. Hierdie puls het veroorsaak dat jong bloekombome wat op B- en DB-behandelings geplant is aansienlik vinniger gegroei het as dié op M- en R-behandelings (tussen 0,4 m en 0,7 m langer op ses maande na aanplanting, en tussen 1,5 cm en 2,0 cm dikker op borshoogte teen elf maande na aanplanting). Groei op DB-behandelings was aansienlik vinniger as selfs dié op B-behandelings, met geen reaksies op enige van die kunsmisbehandelings nie. Bloekombome op M- en R-behandelings het egter 'n sensitiwiteit vir kunsmisbehandelings getoon, met groei wat die meeste verbeter is deur HP-bemesting en die minste deur die onbemeste kontrole. Daar was ʼn betekenisvolle interaksie tussen restebestuur en bemesting. Die M-behandeling het die grootste reaksie op bemesting getoon, asook die swakste algehele groei van bloekombome. Dit is toegeskryf aan die aanvanklike onbeskikbaarheid van grond-N, uitgedruk as grond-C/N-verhoudings groter as 30 en netto immobilisasie na aërobiese inkubasie van grondmonsters. Die R-behandeling het marginaal beter gegroei as die M-behandeling, met 'n vroeë puls van N-mineralisasie wat binne ses maande verdwyn het. Interessant genoeg het die mineralisasiepotensiaal van gronde van alle behandelings geleidelik afgeneem met verloop van tyd: die aanvanklike netto mineralisasie tempo’s het sodanig verlaag dat dit gaandeweg verander het in netto immobilisasie teen die einde van die studieperiode. Dit dui op 'n afnemende substraatkwaliteit met verloop van tyd. Op die tweede perseel, in die Natalse Middellande naby Hilton, is E. grandis x nitens op humiese bogronde met apedale ondergrond aangeplant. Soortgelyke reaksies op die B- en DB-behandelings is binne 'n halfjaar na plant in die grond waargeneem, maar daar is ook gevind dat 'n puls van ammonium vrystelling met hierdie behandelings geassosieer is. In kontras hiermee het die M- en R-behandelings gelei tot 'n puls van nitraat, wat ʼn hoogtepunt bereik het teen vyf maande na aanplanting. Hierdie resultate het korttermyn groeiplek-spesifieke reaksies van oesreste bestuur uitgelig, sowel as vroeë resultate van twee relatief nuwe metodes van oesreste bestuur, naamlik versnippering tot deklaag en in-egting na 'n beheerde brand.en_ZA
dc.description.versionMastersen_ZA
dc.embargo.terms2022-12-24en_ZA
dc.identifier.urihttp://hdl.handle.net/10019.1/125085en_ZA
dc.language.isoen_ZAen_ZA
dc.publisherStellenbosch : Stellenbosch Universityen_ZA
dc.rights.holderStellenbosch Universityen_ZA
dc.subjectForest management -- KwaZulu-Natal (South Africa)en_ZA
dc.subjectAgricultural wastes -- KwaZulu-Natal (South Africa)en_ZA
dc.subjectMulching -- KwaZulu-Natal (South Africa)en_ZA
dc.subjectEucalyptus grandis -- KwaZulu-Natal (South Africa)en_ZA
dc.subjectForest soils -- Fertilization -- KwaZulu-Natal (South Africa)en_ZA
dc.subjectSoil dynamics -- KwaZulu-Natal (South Africa)en_ZA
dc.subjectUCTDen_ZA
dc.titleThe effects of forest residue management on topsoil nutrient dynamics, and on early growth responses of Eucalyptus grandis x urophylla under varied levels of fertilizationen_ZA
dc.typeThesisen_ZA
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