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.