Thesis (MScAgric)--University of Stellenbosch, 2001. / ENGLISH ABSTRACT: The application of water and nutrients via a drip irrigation system influences the water
distribution in the soil, soil characteristics and root distribution beneath the dripper. To
determine the water distribution pattern beneath a dripper in sandy soil, EnviroSCAN
(Sentek) capacitance probes were installed directly below the dripper and at distances of
20, 40 and 60 cm from the dripper. The continuous monitoring of the soil water content
(SWC) beneath the dripper provided a good indication of how the water applied through
the dripper is distributed in the soil. In this study a semi-impermeable layer in the soil
was detected through observing water accumulation patterns in the SWC. Water
accumulated above the layer and SWC values increased to far above the upper level of
easily available soil water (EAWupper),while the lower soil layers remained drier. The
measurements also show that the horizontal water movement is restricted to 20 cm from
the dripper. Specific parameters, such as the lower level of easily available soil water
(EAWlower),can be used to determine optimal irrigation management. Together with the
water distribution study, the root distribution beneath a dripper was also investigated. A
high concentration of roots in the area beneath the dripper was found, which
corresponds with the area wetted by irrigation.
In another study, three irrigationlfertigation methods where investigated to ascertain the
influence on soil characteristics and root distribution. These were: micro irrigation (MI)
(micro-spinner irrigation with broadcast granular fertilization), conventional drip
fertigation (CDF) (daily drip irrigation with daily or weekly fertigation with a
unbalanced nutrient solution, containing macronutrients only) and daily drip fertigation (DDF) (daily fertigation of a balanced nutrient solution, containing macro- and
micronutrients). The study was conducted in two locations, viz. in the Western Cape
Province, on sandy soil, and in the Eastern Cape Province, on silt loam soil.
Micro Irrigation: A wide and even root distribution in the entire wetted volume was
found on the sandy and silt loam soil. On the sandy soil, the soil pH(KC1)directly
beneath the spinner was significantly lower than the pH(KC1)at positions further away
from the spinner.
Conventional Drip Fertigation: Root studies on sandy soil indicate a poor root
development beneath the dripper, with a high concentration of roots in the area between
the drippers. The poor root development directly beneath the dipper may be due to
oxygen deficiency and/or acidification beneath the dripper. The soil pH(KC1)values
show a significant lower pH(KC1)value directly beneath the dripper than further away. In
comparison to the sandy soil, the roots developed well beneath a dripper in a silt loam
soil. It appears as if soil acidity and/or oxygen deficiency was not a problem on this soil
type. The rest of the root system was also well developed. This may be due to this
soil's higher water holding capacity which creates a bigger wetted zone.
Daily Drip Fertigation: In the sandy soil it seems that the roots developed in a
continuous column beneath the dripper line, with little root development further than
20 cm from the dripper line. Where over-irrigation occurred, it caused a poor root
development directly beneath the dripper. The root density in this treatment was much
higher than in the other two treatments. The use of a balanced nutrient solution and
pulse irrigation may be reasons for the better root development. In a silt loam soil a very high concentration of roots was found beneath the dripper and the rest of the root
system was also well developed. As with the CDF treatment, it appears as if oxygen
deficiency was not a problem on this soil type. / AFRIKAANSE OPSOMMING: Die toediening van water en voedingstowwe deur 'n drip-besproeiings stelsel beïnvloed
die waterverspreiding in die grond sowel as die grondeienskappe en wortelverspreiding
onder die dripper. Die waterverspreiding onder 'n dripper in 'n sandgrond is bepaal
deur EnviroSCAN kapasitansie meetpenne direk onder die dripper en 20, 40 en 60 cm
van 'n dripper af te installeer. Die aaneenlopende monitering van die grondwaterinhoud
het 'n goeie indikasie van waterverspreiding in die grond gegee. Die horisontale
waterbeweging is grootliks beperk tot 'n 20 cm radius vanaf die dripper en die
waterbeweging was hoofsaaklik in 'n vertikale rigting. Die teenwoordigheid van 'n
semi-deurlaatbare grondlaag in die grondprofiel is opgemerk deur water-akkumulasie in
die profiel waar te neem. Wortelverspreiding onder die dripper is ook ondersoek en 'n
hoë konsentrasie wortels is in die benatte sone gevind.
In 'n verdere studie is drie besproeiings/sproeibemestings behandelings gebruik om die
invloed van besproeiing/sproeibemesting op grondeienskappe en wortelverspreiding te
ondersoek. Die drie behandelings was: mikro-besproeiing (mikro-besproeiing met
korrelbemesting), konvensionele-drip-sproeibemesting (daaglikse drip-besproeiing met
daaglikse of weeklikse sproeibemesting van 'n ongebalanseerde, voedingsoplossing wat
alleenlik uit makro-elemente bestaan) en daaglikse-drip-sproeibemesting (daaglikse
drip-besproeiing met daaglikse sproeibemesting van 'n gebalanseerde
voedingsoplossing wat mikro- en makro-elemente bevat). Die studie is in twee areas
gedoen, een in die Wes-Kaap, op 'n sandgrond, en die ander in die Oos-Kaap, op 'n
slik-leemgrond. Mikro-besproeiing: Die wortelverspreidings studies op die sand- en slik-leemgrond wys
op 'n wye en eweredige wortelontwikkeling in die totale benatte volume. Op die sand
grond is gevind dat die grond pR(KCl)direk onder die sproeiertjie betekenisvol laer was
as die pR(KCl)waardes verder weg van die sproeiertjie.
Konvensionele-drip-sproeibemesting: Die wortelverspreiding in die sandgrond wys op
geringe wortelontwikkeling direk onder die dripper met die hoogste konsentrasie
wortels tussen die drippers. Grondversuring en/of suurstoftekorte onder die dripper kan
die oorsaak wees van die swak wortelontwikkeling direk onder die dripper. Die grond
pR(KCl)direk onder die dripper was betekenisvol laer as die pR(KCl)verder weg van die
dripper. In vergelyking met die sandgrond, het die wortels in die slik-leemgrond goed
ontwikkelonder die dripper. Dit wil voorkom of versuring en suurstoftekorte onder die
dripper nie 'n probleem was in die slik-leemgrond nie. Die res van die wortelstelsel
was ook goed ontwikkel. Dit mag wees weens die grond se hoë waterhoudingsvermoë
wat 'n groot benatte area tot gevolg het.
Daaglikse-drip-sproeibemesting: In die sand grond wil dit voorkom asof die wortels in
'n aaneenlopende kolom onder die dripperlyn ontwikkel met weinig wortelontwikkeling
verder as 20 cm van die dripperlyn. Waar oorbesproeiing 'n probleem was, was daar
weinig wortelontwikkeling in 'n klein area direk onder die dripper. Die wortel-digtheid
in die behandeling was baie hoër as in die ander behandelings. Die gebruik van 'n
gebalanseerde voedingsoplossing en puls-besproeiing mag dalk redes wees vir die beter
wortelontwikkeling. In die slik-leemgrond is 'n hoë konsentrasie wortels onder die
dripper gevind en die res van die wortelstelsel was ook goed ontwikkel. Soos in die konvensionele-drip-sproeibemesting behandeling wil dit voorkom of suurstoftekort en
versuring onder die dripper nie 'n probleem was in die grond nie.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/52245 |
| Date | 12 1900 |
| Creators | Pijl, Isabelle |
| Contributors | Hoffman, J. E., Rabe, E., Stellenbosch University. Faculty of AgriSciences. Dept. of Horticulture. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | Unknown |
| Type | Thesis |
| Format | 117 p. : ill. |
| Rights | Stellenbosch University |
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