Thesis (MScAgric)--Stellenbosch University, 2012 / ENGLISH ABSTRACT: Biochar has been labelled to be a key factor in the global carbon mitigation act and has
been described as the modern day equivalent (terra nova) to the terra preta dark earth
soils of the Brazilian Amazon. Globally biochar has been evaluated as a means to
improve soil fertility and to mitigate greenhouse gases (GHGs). Little research has
however been published on the effects of biochar incorporation on soil physical
properties.
The objective of this study was to evaluate the effect of pine sawmill waste derived
biochar (locally-produced via slow pyrolysis – 450°C) on selected soil physical
properties, soil-water dynamics and crop production and- performance, when amended
to a Kroonstad (Kd 1000 – Morgendal) soil form. This soil form is commonly found in the
Western Cape area (South Africa) and can be classified as having low agricultural
suitability for perennial- and annual crop species.
Two pot trials were carried out in an atmospheric controlled greenhouse, where winter
wheat and green beans respectively were planted, with five different application levels
of biochar (0t/ha, 1t/ha, 10t/ha, 50t/ha and 200t/ha). Soil physical properties namely,
water-stable aggregates, bulk density and water-retention capacity along with
physiochemical characterisation of the sandy soil and biochar was determined. The
water-use was monitored throughout the trials (evapotranspiration, volumetric water
content and biomass water use efficiency, BWUE). The above- and below ground
(specific leaf traits for the green bean and the root structural development for the winter
wheat) biomass was collected and analysed at harvest.
There was significantly higher volumetric water content measured for the 50t/ha and
200t/ha biochar treatments. This effect can be ascribed due to a change in the soil’s
tortuosity and porosity where more meso- and micro-pores were present as the biochar
rate increased. The same results were evident when a water-retention curve was
established in vitro by means of the sandbox method. The bulk densities were only
significantly lower for the 200t/ha biochar treatments.
The wheat root systems differed greatly among the fertilised biochar treatments: the
50t/ha and 200t/ha treatments had a more complex fibrous root system (more extensive
branching and thinner roots) than 0t/ha, 1t/ha and 10t/ha application levels. This is
attributed to the increased water-holding capacity along with a reduction of N- and P
availability with increasing addition of biochar. Several leaf traits were measured for the
green bean crops; however the leaf nitrogen- and carbon content, chlorophyll content
index (CCI) and carbon isotope fractionation yielded the most interesting findings.
Concerning the fertilised biochar treatments, there was established that the 10t/ha
treatments had the highest leaf nitrogen- and carbon content. The leaf chlorophyll
content did not differ significantly between the fertilised biochar treatments; however a
very interesting observation was evident regarding the measured leaf CCI for the
unfertilised treatments. A decreasing trend and lower leaf CCI was measured as the
biochar application levels increased. This effect was ascribed to be due to a decrease in
N uptake by the plants as the biochar application increased, the C/N ratio also
increased, and this leading to N immobilisation. The lowest leaf carbon isotope
fractionation was measured for the 10t/ha fertilised treatments and is inversely
correlated with BWUE and therefore endorses the conclusion that the 10t/ha biochar
application had a positive effect on the long term water use efficiency for the green bean
plants.
Biochar promoted aggregation in the sand-rhizosphere interface for winter wheat,
increased water-holding capacity and enhanced crop performance for green beans.
The findings reported here provide new information on the effect of biochar on the
structural development of sandy soil, combined with biochar- and root growth effects for
winter wheat; along with detailed interpretations of specific leaf traits associated with
crop production for commercial green beans. The addition of biochar at low application
levels (approximately 1-10t/ha to 15 cm depth) increased the biomass yield and water
use efficiency of the crop species. Besides long term carbon storage, biochar can have
immediate positive effects on the physical properties of sand and plant growth. / AFRIKAANSE OPSOMMING: Biokoolstof word beskou as ‘n sleutel komponent rakende die wet op globale
koolstofvermindering en is al beskryf as die moderne ekwivalent (terra nova) van die
terra preta donker-aardgronde wat aangetref word in die Brasiliaanse Amasone.
Wêreldwyd word biokoolstof tans geëvalueer met die doel om grondvrugbaarheid te
verbeter asook kweekhuisgasse (KHG) se nadelige gevolge te verlig. Min navorsing
was tot dus ver gedoen rakende die uitwerking met toediening van biokoolstof op
grondfisiese-eienskappe.
Die doel van hierdie studie was om die effek van biokoolstof, wat afkomstig is van
denne-saagmeul-afval (plaaslik geproduseer is en d.m.v. stadige perolise - 450°C) te
evalueer aangaande die volgende faktore: geselekteerde grondfisiese-eienskappe,
grond-waterdinamika interaksie en die uitwerking op gewasproduksie; met toediening
aan 'n Kroonstad (Kd 1000 - Morgendal) grondvorm. Hierdie grondvorm word as
algemeen in die Wes-Kaap (Suid-Afrika) bestempel en kan geklassifiseer word as ‘n
lae-geskiktheid landbougrond vir meerjarige- en eenjarige gewasse.
Twee potproewe is uitgevoer onder beheerde atmosfeer in ‘n kweekhuis, waar winter
koring en groenbone geplant is, met vyf verskillende behandelings van biokoolstof
(0t/ha, 1t/ha, 10t/ha, 50t/ha en 200t/ha). Die volgende grondfisiese-eienskappe is
ondersoek, naamlik water-stabiele aggregaat formasie, bulkdigtheid en
waterhouvermoë, asook die fisiochemiese karakterisering van die sanderige grond en
biokoolstof wat gebuik is. Waterverbruik is gedurende die proewe gekontroleer
(evapotranspirasie, volumetriese waterinhoud en die biomassa se water
verbruiksdoeltreffendheid, BWVD). Die bo- en ondergrondse biomassa, spesifiek die
blaareienskappe van die groenboontjie en die strukturele ontwikkeling van die winter
koring se wortels, is tydens die oes ondersoek en ontleed.
Die volumetriese waterinhoud was betekenisvol, asook hoër vir die 50t/ha en
200t/ha behandelings. Hierdie effek word toegeskryf as gevolg van 'n verandering in die
grond se kronkeligheid en porositeit; waar meer meso- en mikroporieë teenwoordig was
soos die biokoolstof inhoud toegeneem het.
Dieselfde resultate was verkry met die opstelling van ‘n water-retensie kurwe in vitro
d.m.v. die Sandboks metode. Bulkdigtheid was slegs betekenisvol verskilled asook
aansienlik laer vir die 200t/ha biokoolstof behandelings. Die koring se wortelstelsel het
drasties verskil tussen die verskillende bemeste biokoolstof behandelings: die 50t/ha en
200t/ha behandelings het 'n meer komplekse en veselagtige wortelstelsel gevorm (hoër
graad van vertakking en dunner wortels was aanwesig) as die 0t/ha, 1t/ha en 10t/ha
behandelings. Die effek word toegeskryf aan die toenemende waterhouvermoë, tesame
met 'n tekort aan N- en P-beskikbaarheid soos die biokoolstof toedieningshoeveelhede
verhoog het. Verskeie blaareienskappe is gemeet vir die groenboon gewasse, maar die
blaar stikstof- en koolstof-inhoud, chlorofil inhoud indeks (CII) en koolstof-isotoop
fraksionering het die mees interessante bevindinge opgelewer. Die hoogste blaar
stikstof-en koolstof-inhoud is gemeet vir die 10t/ha bemeste biokoolstof behandelings.
Die blaar chlorofil inhoud het nie beduidend verskil tussen die bemeste biokoolstof
behandelings nie, maar daar was egter 'n baie interessante waarneming vir die
onbemeste biokoolstof behandelings.
‘n Tendens was aanwesig waar die CII afgeneem het soos die biokoolstof
toedieningshoeveelheid ook afgeneem het vir die onbemeste behandelings.
Die effek word toegeskryf as gevolg van 'n afname in N-opname deur die plant soos die
biokoolstof toedieningshoeveelheid verhoog is en tot gevolg gehad het dat die
C/N-verhouding ook toegeneem het, wat gelei het tot N-immobilisasie. Die laagste blaar
koolstof-isotoop fraksionering was geassioseer met die 10t/ha bemeste biokoolstof
behandelings en is omgekeerd gekorreleerd met BWVD en onderskryf dus die
gevolgtrekking dat die 10t/ha biokoolstof behandeling 'n positiewe uitwerking het op die
langtermyn waterverbruiksdoeltreffendheid vir groenboontjie plante.
Biokoolstof het aggregasie bevorder binne die wortelsone, asook deurgans die
waterhouvermoë verhoog en gewasproduksie verbeter. Hierdie bevindinge lewer nuwe
inligting oor die effek van biokoolstof op die strukturele ontwikkeling van sanderige
grond en die gekombineerde interaksie met biokoolstof toediening en hoe dit wortegroei
beïnvloed van winter koring; asook 'n gedetailleerde interpretasie van spesifieke
blaareienskappe wat verband hou met die produksie van gewasse vir kommersiële
verbouing soos die groenboontjie. Die toediening van biokoolstof by die lae
hoeveelhede (ongeveer 1-10t/ha tot op 15 cm diepte) het die opbrengs en
waterverbruiksdoeltreffendheid van die gewasse verbeter.
Behalwe vir die langtermyn koolstofvaslegging, kan biokoolstof toediening onmiddellike
positiewe resultate teweeg bring aangaande die fisiese eienskappe van sandgronde en
plantegroei.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/20344 |
| Date | 03 1900 |
| Creators | Zeelie, Angelique |
| Contributors | Hoffman, J. E., Hardie, A. G., Stellenbosch University. Faculty of AgriSciences. Dept. of Soil Science. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | Unknown |
| Type | Thesis |
| Format | 126 p. : ill. |
| Rights | Stellenbosch University |
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