| Summary: | Thesis (MScAgric)--University of Stellenbosch, 2003. === ENGLISH ABSTRACT: Poor water management and poor water use efficiency (WUE) have been identified
as one of the major problems experienced by vegetable growers in most of the
developing countries, including South Africa. This poor management and poor
utilization of water have led to a drastic decline in the quality and quantity of
available water. In South Africa agriculture uses about 50% of available water.
Increasing water demand for domestic, industrial and mining uses, may decrease
agriculture's share to less than the current 50%, henceforth, better utilization of this
resource is imperative. Selection of a good irrigation system can limit water loss
considerably. Some irrigation systems have a potential to save more water than
others do.
Since irrigation systems affect the WUE of crops, care should be taken when
selecting an irrigation system under conditions of limited water quantity. Ebb-and-
Flood watering systems have been introduced for effective sub-irrigation and
nutrient delivery within closed systems. Such a system was adapted in South Africa,
to develop a vegetable production unit for use by families in rural communities,
while saving substantial amounts of water. A need to further improve the WUE of
this system was subsequently identified. Two studies were conducted at the
experimental farm of the University of Stellenbosch (Department of Agronomy).
The first trial was conducted under controlled conditions in a glasshouse, and the
second under open field conditions.
In the first trial, Beta vulgaris (Swiss chard) and Amaranthus spp. ('Imbuya') were
grown in two root media; gravel and pumice. In addition, an 'Ebb-and-Flood' and a
'Constant level' system were used with nutrient solutions at two electrical (EC)
conductivity levels 1.80 and 3.60 mS cm-I. The results of this (2x2x2x2) factorial
experiment indicated that a combination of the 'Ebb-and-Flood' system with gravel
as a root medium produced the best results at a low EC, when 'imbuya' was used. A
high total WUE was found with 'imbuya', (7.35 g L-I) at EC 1.80 mS cmicompared
to a relatively low WUE of 5. 90 g L-I when the 3.60 mS cm-I nutrient solution was
used.
In the second trial, 'Imbuya's' foliage dry mass, leaf area and WUE was evaluated
under field conditions at the Stellenbosch University experimental farm, during the summer of2002. The experimental farm (33°55'S, 18°52'E) is situated in the cooler
coastal wine grape-producing region of South Africa with a relatively high annual
winter rainfall. This trial was conducted on an alluvial soil, with clay content of 25%
and a pH of 5.9 (KC!). A closed 'Ebb-and-Flood' system was compared with two
open field irrigation systems ('Drip' and 'Flood') using nutrient solutions at two
electrical conductivity levels (1.80 and 3.60 mS cm-i) in all three cases. Foliage dry
mass, leaf area as well as WUE was best with 'Drip' irrigation, when a nutrient
solution with an electrical conductivity of 3.60 mS cm-i was used. In spite of the
fact that additional ground water was available for the soil grown 'Drip' and 'Flood'
treatments, the 'Ebb-and-Flood' system outperformed the 'Flood' treatment,
especially when the nutrient solution with an EC of 3.6 mS cm-i was used.
Insufficient root aeration in the flooded soil could have been a contributing factor.
The fact that the 'Ebb-and-Flood' and 'Drip' systems gave the best results when the
high EC solution was used to fertigate the plants, may indicate that the plants could
have hardened due to the mild EC stress, better preparing them to adapt to the
extreme heat that was experienced in the field. === AFRIKAANSE OPSOMMING: Swak: bestuur van water en 'n swak: water-gebruik-doeltreffendheid (WOD) is as een
van die belangrikste probleme geïdentifiseer wat deur groente produsente in die
meeste ontwikkelende lande, insluitend Suid-Afrika, ervaar word. Hierdie swak
bestuur en benutting van water het daartoe bygedra dat 'n drastiese afname in die
kwaliteit asook in die kwantiteit van beskikbare water ervaar word. In Suid-Afrika
gebruik die landbou-sektor ongeveer 50% van die beskikbare water. Toenemende
water behoeftes vir huisgebruik, industrieë en die mynbou mag hierdie 50% aandeel
van die landbou sektor laat krimp. Beter benutting van hierdie skaars hulpbron is
dus noodsaaklik. Die keuse van goeie besproeiingsisteme mag waterverliese
merkbaar beperk aangesien sekere sisteme se water-besparingspotensiaal beter as
ander is.
Aangesien besproeiingstelsels die WOD van gewasse beïnvloed, is spesiale sorg
nodig waar 'n besproeiingstelsel onder hierdie toestande van beperkte waterbronne
gekies moet word. 'Ebb-en-Vloed' sisteme kan aangewend word om water en
voedingselemente van onder in 'n wortelmedium te laat opstoot en in 'n geslote
sisteem te laat terugdreineer. So 'n sisteem is in Suid-Afrika ontwikkel waarmee
groente vir families in landelike gebiede geproduseer kan word terwyl water bespaar
word. 'n Behoefte om die WOD van hierdie produksiesisteem verder te verbeter is
egter geïdentifiseer. Twee ondersoeke is by die Universiteit van Stellenbosch se
proefplaas (Departement Agronomie) gedoen. Die eerste proef is onder beheerde
omgewingstoestande in 'n glashuis uitgevoer en die tweede onder veld toestande.
In die eerste proef is Beta vulgaris (Snybeet) en Amaranthus spp. ('Imbuya') in
twee tipes wortelmedia; gruis en puimsteen verbou. 'n 'Ebb-en-Vloed' asoook 'n
'Konstante vlak' besproeiingsisteem is gebruik terwyl voedingsoplossings ook by
twee peile van elektriese geleiding (EC) teen 1.80 en 3.60 mS cm-I toegedien is. Die
resultate van hierdie (2x2x2x2) fakroriaal eksperiment het aangetoon dat 'n
kombinasie van die 'Ebb-en-Vloed' sisteem met gruis as 'n wortelmedium die beste
resultate teen 'n lae EC lewer waar 'imbuya' gebruik is. Die WOD met 'imbuya'
was hoog (7.35 g L-1) by 'n EC van 1.80 mS cm-I, vergeleke met 'n relatief lae
WOD van 5. 90 g L-1 waar die 3.60 mS cm-I voedingsoplossing gebruik is.
In die tweede proef is 'Imbuya' se droë blaarmassa, blaar oppervlakte en WOD
onder veldtoestande op die Universiteit van Stellenbsoch se proefplaas in die somer van 2002 ge-evalueer. Die proefplaas (33°55'S, 18°52'E) is in die koeler kusstreke
van die wyndruif produksiegebied in die winterreëngebied van Suid-Afrika geleë.
Hierdie proef is op alluviale grond met 25% klei en 'n pH van 5.9 (KCi) uitgevoer.
'n Geslote 'Ebb-en-Vloed' sisteem is met twee veld-besproeiingsisteme vergelyk
('Drup' en 'Vloed') terwyl voedingsoplossings teen twee peile van elektriese
geleiding (1.80 en 3.60 mS cm-I) in al drie gevalle gebruik is. Blaar droëmassa,
blaaroppervlakte asook die WGD was die beste met 'Drup' besproeiing waar die EC
van die voedingsoplossing 3.60 mS cm-I was. Ten spyte van die feit dat ekstra
grondwater vir die 'Drup' and 'Vloed' behandelings beskikbaar was, het die 'Ebben-
Vloed' stelsel beter as die 'Vloed' behandeling gedoen veral waar die
voedingsoplossing se EC 3.6 mS cm-I was. Swak wortelbelugting was waarskynlik
die rede waarom vloedbesproeiing swak produksie gelewer het. Die feit dat die
'Drup' en die 'Ebb-en-Vloed' behandelings in die veldproef die beste gedoen het
waar die EC hoog was, mag moontlik met die gehardheid van die plante verband hou
wat aan ekstreem warm en dor toestande blootgestel was.
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