Thesis (MScAgric) -- University of Stellenbosch, 2003. / ENGLISH ABSTRACT: Cowpeas are produced under low and irregular rainfall in most of arid and semi-arid areas of sub-Saharan Africa. Growth and yield are therefore reduced due to the occurrence of water stress during the growing season. Knowledge of the responses and adaptive mechanisms of cowpeas to water stress may help to improve the management practices for these areas. Therefore, three glasshouse experiments were conducted at Welgevallen Experimental Farm of the University of Stellenbosch to test the responses of two cowpea cultivars to water stress. In the first experiment, physiological responses were used to identify those physiological parameters, which can be used to distinguish between drought tolerant and susceptible cowpea cultivars. In the second experiment, some of the identified physiological parameters together with some morphological growth responses, yield and grain protein content of the same two cowpea cultivars were used to identify which is the more tolerant cultivar. Tn the third experiment, the hypothesis that increased phosphorus supply may improve the tolerance of cowpea plants to water stress and their ability of recover from the stress was tested. The results showed that water stress affected water relations, morphological growth parameters, yield and grain protein content, but increasing P supply reduced the effect of water stress and promoted more rapid recovery after re-watering. Water relations were affected by water stress because it reduced relative water content, which resulted in reduced water potential and increased leaf diffusive resistance and proline accumulation. Morphological growth responses and yields were affected because water stress reduced the leaf area, which resulted in reduced biomass production and seed yield. Lower leaf area under water stress was the result of the reduced number of leaves and leaf expansion rate, but the number of leaves was the most important parameter. Reduced seed yield was due to reduced number of pods. The responses of the two cultivars tested were different. AB Wit, which performed better under well-watered conditions was more affected by water stress due to its larger leaf area that resulted in excessive water loss by transpiration. ACH14 was more drought tolerant than AB Wit due to a combination of a more rapid stomatal closure and proline accumulation, which induced osmotic adjustment, and which in tum helped to maintain higher water potentials. The increased P supply reduced the effect of the water stress. High-P level plants showed higher root growth, which resulted in more water uptake and larger leaf area during the water stress period, and after re-watering these plants recovered more rapidly. The more rapid recovery from stress was the result of enhanced root growth and leaf expansion rate and most probably due to increased water uptake. High-P level plants also showed more rapid leaf appearance and plant growth at earlier stages compared to the low-P level plants. / AFRIKAANSE OPSOMMING: Akkerbone word onder toestande van lae en wisselvallige reenval in baie ariede en semi-ariede gebiede van Afrika verbou. In hierdie gebiede word groei en produksie dikwels beperk deur water tekorte gedurende die groei seisoen. Kennis van reaksies en aanpassingsmeganismes van akkerbone teenoor water tekorte mag dus help om produksietegnieke in bogenoemde gebiede te verbeter. Om hierdie rede is drie glashuiseksperimente onder gekontroleerde toestande op die Welgevallen Proefplaas van die Universiteit van Stellenbosch uitgevoer. In die eerste eksperiment is fisiologiese reaksies van twee cultivars gebruik om eienskappe te identifiseer wat gebruik kan word om tussen droogteweerstandbiedende en droogte gevoelige cultivars te onderskei. In die tweede eksperiment is sommige van die geidentifiseerde eienskappe asook morfologiese groei, opbrengs en kwaliteitsreaksies van dieselfde twee cultivars gebruik om die meer droogte weerstandbiedende cultivar te identifiseer. In die derde eksperiment is die hipotese dat P-bemesting die droogteweerstandbiedendheid teen en herstelvermoe na droogte kan verbeter, getoets. Die resultate toon dat water tekorte beide plantwaterverhoudings, morfologiese eienskappe asook opbrengs en proteieninhoud beinvloed, maar dat hoe P-peile die invloed van water tekorte verminder en herstelverrnoe na die droogte verbeter. Plant-waterverhoudings is bemvloed omdat water tekorte relatiewe waterinhoud van plante verlaag wat aanleiding gee tot verlaagde plantwaterpotensiale, verhoogde huidmondjie weerstand en 'n toename in prolien inhoud. Morfologiese eienskappe en opbrengs is benadeel weens 'n veri aging in blaaroppervlakte wat fotosintetiese vermoe en gevolglik ook biomassaproduksie en saad opbrengs benadeel. Verlaagde blaaroppervlakte tydens water tekorte was hoofsaaklik die gevolg van 'n vermindering in aantal blare, terwyl verlaagde saadopbrengs grootliks die resultaat van 'n vermindering in aantal peule was. Die cultivar AB Wit wat die hoogste opbrengs onder gunstige groeitoestande gelewer het, is die meeste bemvloed deur water tekorte omdat die welige blaargroei van hierdie cultivar, luukse waterverbruik en groter transpirasie verliese veroorsaak het. Die cultivar ACH 14 daarteenoor het waterverliese beperk deurdat die huidmondjies vinniger gesluit het en verhoogde prolien-inhoude, osmotiese aanpassings veroorsaak het. Dit het gehelp om waterpotensiale instand te hou. Hierdie cultivar was gevolglik meer droogte weerstandbiedend as AB Wit. Hoe vlakke van P-bemesting het die effek van water tekorte verminder weens verbeterde wortelgroei. Dit het wateropname gedurende en na die peri ode van water stremming verbeter sodat plante vinniger herstel het na die droe periode. Plante wat by hoe P-peile gegroei is het ook 'n verhoogde blaarverskyningstempo en 'n toename in groei tydens die vroee ontwikkelingstadiums getoon.

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.

Thesis (MSc)--University of Stellenbosch, 2002. / ENGLISH ABSTRACT: The effects of regulated deficit irrigation on the production and fruit quality of peaches were investigated. A field trial was carried out in a twelve-year-old Neethling peach orchard at Robertson Experiment Farm. Treatments consisted of five different soil water depletion levels applied during five different growth stages. Irrigation was applied at the five soil water depletion levels of which T1 was regarded as relatively wet (irrigation was applied when the average soil matric potential reached ca. -50 kPa). T2 was regarded as normal (irrigation applied at ca. -100 kPa) and three different deficit irrigation regimes T3, T4 and T5, irrigated at soil matric potentials of ca. -200, -400 and -800 kPa respectively. The five growth stages were Stage 1 (cell growth), Stage 2 (slow fruit growth), Stage 3 (rapid fruit growth), Stage 4 (ripening) and Stage 5 (post-harvest). The soil water content was monitored and irrigation was scheduled by means of a neutron probe. Vegetative and fruit growth, fruit mass and production were measured. Fruit were examined for bruises and firmness. Fruit size, fruit mass, fruit quality, as well as production, were not sensitive to water deficits during the different growth stages with a normal crop load. However, a tendency to reduced shoot growth with decreasing soil matric potentials was observed during the slow fruit growth, rapid fruit growth as well as the ripening stages. The application of deficit irrigation during the slow fruit growth or post-harvest stages can save substantial amounts of water with a normal crop load, provided that normal irrigation is applied during the other growth stages. A combination of water deficits during the ripening stage and high crop load resulted in smaller fruit and lower production. Fruit size, fruit mass, fruit quality, as well as production, were not sensitive to water deficits during either the cell growth, slow fruit growth or post harvest growth stages, provided that normal irrigation is applied in the other growth stages. Irrespective of crop load, soil matric potentials up to -200 kPa can be applied during anyone of the growth stages without seriously affecting the final fruit size, fruit mass, fruit quality or production. However, this soil water deficit may then only be applied in one of the growth stages and normal irrigation must be applied in the other four stages. Although deficit irrigation reduced seasonal water consumption, it could not be justified as water saving with a heavy crop load. / AFRIKAANSE OPSOMMING: Die effekte van gereguleerde tekort besproeiing op die produksie en vrugkwaliteit van perskes is ondersoek. 'n Veldproef is in 'n twaalf-jaar-oue Neethling perskeboord te Robertson Proefplaas uitgevoer. Die behandelings het bestaan uit vyf grondwater-ontrekkingspeile wat gedurende vyf verskillende groeistadiums toegepas is. Besproeing is toegedien by vyf verskillende grondwaterontrekkingsvlakke waar T1 beskou is as redelik nat (besproeiing is toegedien wanneer gemiddelde grondmatrikspotensiale ca. -50 kPa bereik het). Behandeling T2 is as normaal beskou (besproeiing toegedien by ca. -100 kPa en drie verskillende regimes van tekort besproeiing naamlik T3, T4 en T5 wat onderskeidelik by ca. -200, -400 en -800 kPa besproei is. Die vyf groeistadiums was onderskeidelik Stadium 1 (selgroei), Stadium 2 (stadige vruggroei), Stadium 3 (vinnige vruggroei), Stadium 4 (rypwording) en Stadium 5 (na-oes). Die grondwaterinhoud is gemonitor en die besproeiing is met behulp van 'n neutronpeiler geskeduleer. Vegetatiewe groei, vruggroei, vrugmassa en produksie is gemonitor. Vrugte is ook ondersoek vir kneusbaarheid en fermheid. Geen negatiewe effek as gevolg van watertekorte is ten opsigte van vruggrootte, -massa, -kwaliteit sowel as produksie waargeneem gedurende die verskillende groeistadiums waar 'n normale vruglading gehandhaaf is nie. 'n Afnemende tendens in lootgroei met afnames in grondwatermatrikspotensiale is egter gedurende die stadige- en vinnige vruggroei-stadiums, asook in die vrugrypwordingstadium, waargeneem. 'n Aansienlike hoeveelheid water kan bespaar word deur gereguleerde tekort besproeiing gedurende die stadige vruggroei- of na-oes-stadiums toe te pas, mits 'n normale vruglading gehandhaaf word en normale besproeiing in die ander groeifases toegedien word. 'n Kombinasie van watertekorte en 'n hoë vruglading gedurende die rypwordingstadium het tot kleiner vrugte en laer produksies gelei. Vruggrootte, -massa, -kwaliteit en produksie is egter nie gevoelig vir watertekorte gedurende die selgroei-, stadige vruggroei- en na-oes-stadiums nie. Tekort besproeiing by 'n grondwatermatrikspotensiaal van tot -200 kPa kan egter met 'n normale en hoë vruglading in enige van die fases toegepas word, sonder om die finale vruggrootte, -massa, - kwaliteit of produksie nadelig te beïnvloed. Hierdie tekort besproeiingsregime mag egter slegs in een van die groeistadiums toegedien word en normale besproeiings moet in die ander groeistadiums toegedien word. Alhoewel tekort besproeiing die seisoenale waterverbruik verminder het, kan dit nie geregverdig word as 'n waterbesparende praktyk indien 'n hoë vruglading gehandhaaf word nie.

This study examined features of deep pool (>0.8 m mean depth) used by adult summer steelhead in Steamboat Creek (1991-1992). Steamboat Creek had a heterogenous thermal profile, with some segments exceeding preferred temperature of steelhead. Deep pools were scarce (4% of the total habitat units) and 39% of them were identified as cool pools (mean bottom water temperature [less than or equal to] 19°C). Adult summer steelhead were found primarily in deep pools, avoiding other habitats (glides, riffles) and even cold but shallow tributary junctions. Use of odds ratio showed that use of cool pools use was estimated to be 11 times greater than the odds of the use of warm pools (P <0.001). Discriminant analysis identified mean bottom pool water temperature, riparian forest at the pool bank, proportion of large boulders, maximum length and mean depth as the best subset of variables that accounted for differences between pools occupied and not occupied by adult steelhead. A total of 69% of the variation was explained by differences in used and not used groups. Classification accuracy was 89%. Canton Creek, a tributary of Steamboat Creek, were tested as validation site for the derived model, observing that the classification function performed moderately, achieving a hit-ratio of 0.7. Results of the study showed that, since bottom pool temperature was a major factor but other ecological factors were also relevant, an integrated framework would be required in determining pool used by this species. Moderate success of the predictive model suggests that managers will want to check it before applying in other basins. / Graduation date: 1995

No description available.

The performance of three maize (Zea mays L.) hybrids, grown under two irrigation levels, was used to investigate the effects of soil moisture competition between adjacent plots, the transmission of these effects into multi-row adjacent plots and types of multi-row plots and plot borders most effective in shielding from these interplot competition effects. On the basis of grain yield, competition effects intended to the second rows of five-row plots necessitating more than five-row plots to accurately evaluate the full transmission of interplot competition effects into adjacent plots. Evaluation of genotypes in one-row plots all with the same common border row genotype to make them three-row plots would be more suitable for evaluation of relative competitiveness for soil moisture under soil moisture stress conditions compared to no border rows or border rows of the same genotype being evaluated.

Typescript (photocopy). / Digitized by Kansas Correctional Industries

Severe water stress reduced the number of flowers produced by Capsicum annuum var. annuum L. Longum plants, but the timing of flower production was less affected. The use of different plant establishment techniques modified flower production. Bare rooted transplants slowed the rate of flower production in comparison with direct seeded plants or those established from cell tray transplants. Bare rooted transplants delayed the onset of water stress. The capabilities of male and female gametophytes were reduced by water stress, with the female more affected, and the interaction of male and female gametophytes was affected by moderate water stress. Moderate water stress increased the time to fruit set, but affected neither the number nor percentage of fruit set, whereas severe water stress increased the time and reduced the number and percentage. Severe water stress reduced the number and percentage of mature fruit, fruit quality indices and total fruit yield. Moderate water stress reduced the number of seeds per fruit and fruit dry weight, but total fresh weight yield was not significantly affected. The time to fruit set was negatively correlated with the quality indices of mature fruit, whereas the number of seeds was positively correlated with the same. Fertilisation determined the success of seed set, and the rapidity of fruit set. Successful fertilisation can only occur when the pollen tube arrives at a viable ovule. The processes of pollen tube growth and longevity of the ovule are the factors most critically affected by water stress in determining the yield of C. annuum Longum. / Master of Science (Hons)

Some ill. mounted. Bibliography: leaves 106-118.

Includes bibliographies. This thesis describes an irrigation experiment established on Vitis vinifera cv. Shiraz in a mature vineyard in the Australian Murray-Darling basin. It concentrates on the relationship between the timing of the water deficit and the depth of irrigation applied and the difference in berry weight between different irrigation treatments. The study includes a polynomial equation which describes the relation between growing degree days and °Brix. A two phase linear model is used to describe the change in red-free glycosyl-glucose (G-G).