Thesis (MscFor)--Stellenbosch University, 2011. / ENGLISH ABSTRACT: The purpose of the study was to investigate the effect of mid rotation fertilizer application
on leaf area index (LAI), basal area and volume increment in thinned Pinus radiata stands
on the most common soils of the Boland region in the Western Cape.
The study was conducted on a range of sites in the Boland region of MTO Forestry
Company, chosen to reflect the two most common soil types and a water availability
gradient in each soil type. A factorial combination of fertilizer treatments with three levels
each for nitrogen (N) at 0, 100 and 200 kg ha-1 and phosphorus (P) at 0, 50 and 100 kg ha-
1 was used. This design was replicated four times across a gradient of water availability
for each of the two common soil groups, forming a complete trial series. All replications
were laid out in P. radiata stands that had received their mid-rotation thinning prior to
treatment implementation.
LAI, diameter at breast height and height measurements as well as foliar analysis were
determined before the implementation of the study in 2008 and then subsequently at
predetermined intervals in 2009 and 2010. Leaf area index and stem volume increment
were measured in order to evaluate the influence on growth efficiency. LAI was estimated
using the gap fraction method with the use of a ceptometer. Volume increment was
calculated using diameter and height measurements and basal area was calculated by
means of diameter measurements. The abovementioned growth responses were then
used to determine the effect of increased nutrient availability on stand growth.
There were no significant interactions detected between any of the factors, N, P and water
availability class in their effect on LAI, basal area, volume increment and growth efficiency.
LAI increment responded significantly to N and P in the first year but only to P in the second year after treatment. Significant basal area responses to N and P were recorded
in the second but not the first year. This might have been due to the fact that trees had to
re-build their canopies after thinning before a basal area response could be obtained. For
the variables where an analysis of total growth response over the two year period was
done, basal area increment and volume increment significantly responded to the
application of nitrogen but not to phosphorus. Growth efficiency was not significantly
influenced by either nitrogen or phosphorus over the full two year monitoring period.
Water availability class consistently and significantly influenced basal area increment,
volume increment and growth efficiency over the two year period as well as during year
one and year two.
The best responses generally occurred as a result of the additive effects of N and P. The
growth response did not remain the same across the water availability classes. The wetter
sites tended to have greater responses than the drier sites. Although these are still early
results, the growth responses could be attributed to an increase in LAI. Nutrient analysis
through vector analysis indicated that the additional N and P from fertilizer application
were taken up by the trees thereby resulting in greater LAI and increased stem wood
production. / AFRIKAANSE OPSOMMING: Die studie het ten doel gestel om die effek van mid-rotasie bemesting op blaar oppervlak
indeks (BOI), basale oppervlakte- en volume aanwas te ondersoek in gedunde opstande
van Pinus radiata op die mees algemene grondtipes van die Bolandstreek, Wes-Kaapland.
Eksperimente is uitgelê oor 'n reeks van groeiplekke in die Bolandstreek wat gekies is om
'n water beskibaarheidsgradient te verteenwoordig oor elk van die twee mees algemene
grondtipes. 'n Faktoriaal-kombinasie van kunsmisbehandelings met drie vlakke elk van
stikstof [(N) teen 0, 100 en 200 kg ha-1] en fosfor [(P) teen 0, 50 en 100 kg ha-1] is
toegedien. Hierdie ontwerp is vier maal herhaal oor 'n gradient van grondwater
beskikbaarheid, oor elk van die twee mees algemene grondtipes, om sodoende 'n
volledige eksperimentele reeks te vorm. Elke herhaling is uitgelê in 'n P. radiata opstand
wat reeds 'n mid-rotasie dunning ondergaan het voor implementering van die kunsmis
behandelings.
Metings van BOI, deursnee op borshoogte, boomhoogte asook blaarmonsters is geneem
voor implementering in 2008 en daarna met vooraf bepaalde tussenposes in 2009 en
2010. Die BOI en stam volume aanwas is bepaal om die effek van behandelings op groeieffektiwiteit
te evalueer. Die gaping fraksie tegniek is gebruik om BOI te skat met behulp
van 'n sonvlek septometer. Volume aanwas is bereken vanaf deursnee en hoogtemetings
en basale oppervlak aanwas vanaf deursnee-metings. Metings van al bogenoemde
groeireaksies is gebruik om die effek van verhoogde voedingstof beskikbaarheid op
opstandsgroei te evalueer.
Daar was geen betekenisvolle interaksies tussen enige van die faktore N, P of water
beskikbaarheidsklas met betrekking tot reaksies op BOI, basale oppervlak- en volume aanwas of groei-effektiwiteit nie. Die BOI het betekenisvol gereageer op N en P in die
eerste jaar, maar slegs op P in die tweede jaar na behandeling. Basale oppervlakte
aanwas is betekenisvol verbeter deur N en P in die tweede jaar maar nie in die eerste jaar
nie. Dit is waarskynlik as gevolg van die feit dat opstande eers hul kroondak moes herstel
(na dunnings) voordat 'n reaksie in basale oppervlak verkry kon word. Vir die
veranderlikes waar 'n analise van die groeireaksie oor die volle twee jaar
moniteringsperiode gedoen is, het basale oppervlak- en volume aanwas betekenisvol
gereageer op stikstof maar nie op fosfor nie. Groei-effektiwiteit is nie betekenisvol
geaffekteer deur N of P oor die volle twee jaar moniteringsperiode nie. Water
beskikbaarheidsklas het basale oppervlak en volume aanwas asook groei-effektiwiteit
betekenisvol en voortdurend beïnvloed in die eerste en tweede jaar, asook gedurende die
volle twee jaar moniteringsperiode.
Die beste groeireaksie is oor die algemeen verkry waar N en P gesamentlik toegedien is
en waar dus aanvullende reaksies verkry is. Groeireaksies het betekenisvol verskil na
gelang van water beskikbaarheidsklas, met die grootste reaksie op die natste groeiplekke.
Hoewel hierdie vroeë resultate is, kan ons die meganisme van die reaksie primêr toeskryf
aan 'n toename in BOI. Vektor analise van blaar voedingstof vlakke het aangedui dat
addisionele N en P na kunsmis toediening opgeneem is, wat die weg gebaan het vir 'n
toename in BOI en verhoogde volume aanwas.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/17828 |
| Date | 12 1900 |
| Creators | Chikumbu, Vavariro |
| Contributors | Du Toit, Ben, Stellenbosch University. Faculty of AgriSciences. Dept. of Forest and Wood Science. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | Unknown |
| Type | Thesis |
| Format | 174 p. : ill., maps |
| Rights | Stellenbosch University |
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