Thesis (MScAgric)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: Limited research is available on the effect of mulches on established orchards. Most of the information available stems from research conducted in newly planted orchards or on annual crops such as green peppers and strawberries under greenhouse conditions. To increase the current knowledge on the effect of mulches in established orchards, two field trials were conducted on 14 year old „Cripps‟ Pink‟ orchards. The one trial concentrated on the influence of mulches on the root environment and the other trial on the effect of mulches on growth, yield and fruit quality. Both trials were conducted at Lourensford Estate near Somerset West, but the sites differed in soil texture between lighter soil (Tukulu) and heavier soil (Clovelly). Four different mulches were used viz. compost, wood chips, vermi-castings (topped with thin layer of woodchips) and a woven geotextile fabric. These four treatments were compared to an un-mulched control, managed according to industry norms. After reducing irrigation volume in the 2010/2011 season, with a further reduction in the 2011/2012 season, more significant differences were obtained in nutrient levels of fruit and leaves compared to the 2008/2009 and 2009/2010 seasons of the trial. Leaf and fruit nutrients showed significant differences in both sites, but the differences were more pronounced on the lighter soil. At the heavier soil site, the vermi-castings, woodchips and compost treatments increased fruit phosphorus (P) during 2010/2011 and the control treatment increased fruit boron (B) during 2011/2012. Only leaf magnesium (Mg) was increased by woodchips and vermi-castings in 2011/2012 at this site. In the lighter soil site, the control treatment had the highest fruit B levels in 2010/2011 while the vermi-castings and the woodchips treatments had the highest fruit P levels in 2011/2012. For the same site, vermi-casting and compost treatments improved leaf potassium (K) uptake in 2010/2011 and 2011/2012, whereas woodchips and geotextile significantly improved leaf copper (Cu) uptake in 2010/2011 compared to the control. To determine if applied nutrients were trapped in the organic mulches over time, leading to a deficiency in the soil and eventually the tree, a mineral analysis was conducted on the organic mulches at the end of each season. Results of the two seasons indicated that vermi-castings contained higher total nutrient levels than the other two organic mulches, but the difference in nutrient levels were shown not to be directly related to the fertilisers applied during each season. In the case of vermi-castings, nutrient quantities in the original material applied at the beginning of each season were higher than those of the other organic mulches. The higher nutrient levels in organic in comparison to inorganic mulches were however not reflected in the fruit and leaf mineral analysis of these treatments. The overall treatment effect in terms of changes in nutrient levels in the tree became less significant when trees were over irrigated. This became evident as the differences between mulching treatments increased as the irrigation was reduced during the season, indicating the masking effect of irrigation on mulching. Evaluating the effect of mulches on growth, yield and fruit quality showed significant differences only at the heavier soil site. The vermi-casting treatment had significantly higher yield efficiencies than the control for the 2010/2011 season. Compost had the lowest yield efficiency at both sites, also during the previous two seasons that formed part of an earlier study (Kotze 2012). In 2011/2012, the compost treatment also showed significantly higher shoot growth than the control. Compost therefore could increase vegetative growth in established orchards on a heavier soil after application for four seasons. Taking the cost of mulching into account, wood chips are the only treatment that can be recommended without compromising fruit quality. Wood chips will sustain or even improve yield efficiency in an established orchard on especially heavier soil. Future research should study the effect of different amounts of irrigation on the various mulches, as the effect of irrigation was not evaluated in this study. / AFRIKAANSE OPSOMMING: Beperkte navorsing is beskikbaar oor die effek van deklae op bestaande boorde. Die meeste bestaande inligting is gegrond op proewe wat uitgevoer is op nuut aangeplante boorde of op eenjarige gewasse, soos groenrissies en aarbeie, onder kweekhuis toestande. Om bestaande kennis aan te vul rakende die effek van deklae op vrugproduksie en -kwaliteit in bestaande boorde, is twee veldproewe geloots in 14-jaar-oue „Cripps‟ Pink‟ appelboorde. Die een proef het gekonsentreer op die invloed van deklae op die wortel omgewing en die ander proef, op die effek van deklae op groei, opbrengs en vrugkwaliteit. Beide proewe is uitgevoer op Lourensford Landgoed naby Somerset-Wes en twee verskillende grondtipes is hiervoor gebruik: „n ligte grond (Tukulu) en swaarder grond (Clovelly). Vier verskillende deklaagtipes is gebruik naamlik: kompos, houtspaanders, „vermi-castings‟ (bedek met „n dun lagie houtspaanders) en geweefde geotekstiel materiaal. Hierdie vier behandelings is vergelyk met „n onbedekte kontrole wat volgens industrie norm bestuur is. Nadat die besproeiingsvolume verminder is in 2010/2011 en daarna weer in 2011/2012, het meer betekenisvolle verskille tussen behandelings voorgekom in nutriënt-vlakke van vrugte en blare in vergelyking met die eerste twee jaar van die proef (2008/2009 en 2009/2010). Blaar en vrug nutrient-vlakke het betekenisvolle verskille in beide persele getoon, maar die verskille was meer duidelik in die ligte grondtip. In die swaarder grond perseel het die „vermi-castings‟, houtspaanders- en kompos behandelings die vrug fosfaatvlakke (P) betekenisvol verhoog in 2010/2011. In die kontrole behandeling was vrug boorvlakke (B) betekenisvol hoër as die ander behandelings in 2011/2012. In hierdie perseel is net magnesium-vlakke (Mg) in die blare betekenisvol verhoog deur die houtspaanders- en „vermi-castings‟ behandelings in 2011/2012. In die ligte grond perseel het die kontrole behandeling die hoogste vrug B-vlakke in 2010/2011 gehad en die „vermi-castings‟ en houtspaander-behandelings gesamentlik, die hoogste vrug P-vlakke in 2011/2012. Die „vermi-casting‟ en kompos behandelings het kalium-vlakke (K) opname in die blare in 2010/2011 en 2011/2012 verbeter, terwyl die houtspaanders- en geotekstiel behandelings die koper-vlakke (Cu) in die blare in 2010/2011 verbeter het. Om te bepaal of die toediening van voedingstowwe oor tyd kan lei tot die „vashou‟ daarvan in „n organiese deklaag en dan tekorte van sekere nutriënte in die grond en uiteindelik die boom kan veroorsaak, is „n mineral analise van die organiese deklae uitgevoer aan die einde van beide seisoene. Resultate van die twee seisoene het getoon dat „vermi-castings‟ hoër totale nutrient-vlakke gehad het as die ander organiese deklae, maar die nutrient-vlakke was nie direk verwant aan die toegediende voedingstowwe nie. In die geval van „vermi-castings‟, was nutrient-vlakke van die moedermateriaal, wat toegedien is aan die begin van die seisoen, hoër as die van die ander organiese deklae. Hierdie hoër nutrient-vlakke van die organiese teenoor anorganiese behandelings, is nie gereflekteer in hoër nutrient-vlakke in die vrug- en blaar mineraal analises van die bome nie. Behandelings effekte rakende veranderinge in nutrient-vlakke in die boom, nadat die besproeiing verminder is, het verander in vergelyking met die van die vorige twee seisoene en is „n aanduiding van die verbloemende invloed van besproeiing op die prestasie van deklae. Evaluasie van die effek van deklae op groei, opbrengs en vrugkwaliteit het net betekenisvolle verskille in die swaarder grond perseel getoon. Die „vermi-casting‟-behandeling het „n betekenisvolle hoër opbrengseffektiwiteit as die kontrole getoon in 2010/2011. Kompos het die laagste opbrengseffektiwiteit in beide persele gehad en het resultate van die vorige twee seisoene van Kotze (2012) bevestig. Die betekenisvolle hoër lootgroei van kompos as die ander behandelings het net in 2011/2012 voorgekom. Kompos kan dus groei verhoog in „n gevestigde boord, in „n swaarder grond, indien besproeiing optimaal is. In terme van kostes, word die gebruik van houtspaanders as deklaag voorgestel vir „n gevestigde boord met „n swaar slik leem grond, aangesien daar geen nadelige effek op vrugkwaliteit was met die behandeling nie en die opbrengseffektiwiteit van die bome gehandhaaf en selfs verbeter is. Toekomstige navorsing kan die effek van besproeiing op verskillende deklaag tipes bestudeer, aangesien die bestaande proef dit nie kon aanspreek nie.

Doctor of Philosophy (PhD) / The Flesh Browning (FB) disorder of ‘Cripps Pink’ apples presents a significant threat to the established market identity of the ‘Cripps Pink’ apple in Australian and export markets. Climatic conditions during fruit growth and development predispose ‘Cripps Pink’ apples to developing the FB disorder during storage. The FB disorder can be classified into two distinct disorders based on their physiological and structural differences and by seasonal climatic conditions. The diffuse type of FB (DFB) is a chilling injury, occurring in districts or seasons accumulating less than 1100 growing degree days (GDD) above 10oC between full bloom and harvest. In these climatic conditions, ‘Cripps Pink’ apples have delayed postharvest ethylene production. Diffuse FB effects fruit cortex tissue and is characterised as cellular collapse. Storing fruit at 3oC can reduce the incidence of DFB. The radial type of FB (RFB) is primarily a senescent disorder, occurring in districts or seasons accumulating greater than 1400 GDD above 10oC between full bloom and harvest. In these climatic conditions, postharvest ethylene production is not delayed. Radial FB affects the cells adjacent to the vascular tissue of the fruit and is characterised by damaged cell walls. Storing fruit at 1oC can reduce the incidence of RFB. Harvest maturity and the level of CO2 in the storage atmosphere are additive influences on the development of RFB. Seasons or districts accumulating more than 1700 GDD have a very low risk for developing RFB. Seasonal climatic conditions can provide a guide for predicting the risk of developing RFB and DFB during storage.

Doctor of Philosophy (PhD) / The Flesh Browning (FB) disorder of ‘Cripps Pink’ apples presents a significant threat to the established market identity of the ‘Cripps Pink’ apple in Australian and export markets. Climatic conditions during fruit growth and development predispose ‘Cripps Pink’ apples to developing the FB disorder during storage. The FB disorder can be classified into two distinct disorders based on their physiological and structural differences and by seasonal climatic conditions. The diffuse type of FB (DFB) is a chilling injury, occurring in districts or seasons accumulating less than 1100 growing degree days (GDD) above 10oC between full bloom and harvest. In these climatic conditions, ‘Cripps Pink’ apples have delayed postharvest ethylene production. Diffuse FB effects fruit cortex tissue and is characterised as cellular collapse. Storing fruit at 3oC can reduce the incidence of DFB. The radial type of FB (RFB) is primarily a senescent disorder, occurring in districts or seasons accumulating greater than 1400 GDD above 10oC between full bloom and harvest. In these climatic conditions, postharvest ethylene production is not delayed. Radial FB affects the cells adjacent to the vascular tissue of the fruit and is characterised by damaged cell walls. Storing fruit at 1oC can reduce the incidence of RFB. Harvest maturity and the level of CO2 in the storage atmosphere are additive influences on the development of RFB. Seasons or districts accumulating more than 1700 GDD have a very low risk for developing RFB. Seasonal climatic conditions can provide a guide for predicting the risk of developing RFB and DFB during storage.

Thesis (MScAgric)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: An investigation into the effects of different mulches on the root environment, encompassing physical, chemical and biological factors of the soil, on two different soil types was done in the form of a field trial on ‘Cripps’ Pink’ apples. Three organic mulches were tested: compost, vermi-castings and woodchips, as well as an inorganic mulch, geotextile fabric, and were compared against clean cultivation. The organic treatments resulted in improved physical conditions (lower bulk densities) in the heavier soil, as well as, a reduction in temperature fluctuations and a general increase in soil temperatures during the seasons, in both sites. The geotextile fabric treatment resulted in increased soil moisture levels in the top 40 cm, predominantly in the heavier soil. The compost treatment resulted in high soil moisture levels in the top 40 cm only in the lighter soil. The vermi-castings treatment achieved superior results in terms of changing the nutrient status of the heavier soil. It resulted in significantly higher pH, P (phosphorus), N (nitrogen), K (potassium), Mg (magnesium), Zn (zinc), Mn (Manganese), B (boron), as well as the cation exchange capacity and some exchangeable cations, such as, Na+ (sodium ions), K+ (potassium ions) and Mg+ (magnesium ions). The compost treatment resulted in significantly higher Ca (calcium) and Ca+ (calcium ions) in the heavier soil compared to the other treatments. The organic mulches, including the woodchips treatment, consistently resulted in higher mineral levels and therefore performed the best in this regard and did so in the heavier soil. In contrast to the heavier soil, none of the treatments were successful in ameliorating the nutrient status of the lighter soil, with the exception however of the increased percentage C as a result of the compost and vermi-castings treatments. The compost treatment realised consistently higher mychorrizael colonization in both sites, however, not always significantly higher than the other treatments. The vermi-castings treatment realised consistently lower plant parasitic nematodes numbers. Higher free-living nematodes were also frequently realised during both seasons and in both sites. The organic mulches therefore proved promising with regard to soil biota. The organic treatments, with the exception of the vermi-castings treatment, resulted in improved root number and distribution in the heavier soil. The vermi-castings treatment resulted in a superior root environment and did not need to enhance its root system in order to achieve good fruit yield and quality. In contrast, the geotextile fabric treatment performed better in this regard in the lighter soil. The geotextile fabric treatment also achieved the lowest weed counts, quantified as winter weeds, in both sites. Yield efficiency, in the heavier soil, and the incidence of sunburn in both sites, were influenced by mulching. In the heavier soil, the woodchips treatment resulted in the highest yield efficiency and the compost treatment consistently resulted in the highest incidence of sunburn. In the lighter soil the control treatment resulted in the highest incidence of sunburn. The vermi-castings treatment consistently resulted in lower incidences of sunburn. Due to the limited quantification of irrigation in this trial, the consequence of irrigation on different mulches was not evaluated and should be considered for future research. / AFRIKAANSE OPSOMMING: ‘n Ondersoek na die effek van verskillende deklae op die wortelomgewing, insluitende fisiese, chemiese en biologiese grond faktore, is uitgevoer as ‘n veldproef of twee verskillende grondtipes, op ‘Cripps’ Pink’ appels. Drie organiese deklae is ge-evalueer naamlik: kompos, ‘vermi-castings’ en houtspaanders, asook ‘n anorganiese geotekstiel materiaal deklaag, en vergelyk met ‘n kontrole van skoon bewerking. Die organiese behandelings het verbeterde fisiese kondisies (laer bulkdigtheid) in die swaarder grond, asook ‘n verlaging in temperatuur fluktuasies en algemene verhoging in grondtemperature gedurende die seisoene in beide persele tot gevolg gehad. Die geotekstiel behandeling het verhoogde grondvog-vlakke in die boonste 40 cm in beide persele tot gevolg gehad, alhoewel dit meer prominent in die swaarder grond was. In sanderige grondperseel, het die kompos behandeling hoër grondvog-vlakke in die boonste 40 cm getoon as die ander behandelings. Die ‘vermi-castings’ behandeling het die beste resultate in terme van verbetering van nutrient- vlakke in die swaarder grond behaal. Dit het ‘n betekenisvol hoër pH, P (fosfaat), N (stikstof), K (kalium), Mg (magnesium), Zn (sink), Mn (mangaan), B (boron), katioon uitruilings kapasiteit en sommige uitruilbare katione soos , Na+ (natrium ione), K+ (kalium ione) en Mg+ (magnesium ione) as die ander behandelings in die swaarder gehad. Die kompos behandeling het betekenisvol hoër Ca (kalsium) en Ca+ (kalsium ione) in die swaarder grond getoon. Die organiese behandelings, insluitend die houtspaander behandeling, het dus in die geval, konstant die beste resultate te opsigte van hoër nutriënt vlakke in die swaarder grond getoon. Inteenstelling met die swaarder grond, het geen behandling daarin geslaag om die grondvoedingstatus van die sanderige grond te verbeter nie, met uitsondering die verhoogde persentasie C as ‘n resultaat van die kompos en ‘vermi-castings’ behandelings. Die kompos behandeling het konstant hoër mychorriza-kolonisasie teweeg gebring in beide persele, alhoewel nie altyd betekenisvol hoër as die ander behandelings was nie. Die ‘vermicastings’ behandeling het konstant ‘n laer persentasie plant-parasitiese nematodes getoon. Meer vry-lewende nematodes het ook gereeld oor die totale vier jaar wat die volledige proef gestrek het, op beide persele, voorgekom. Die organiese deklae toon dus belowende resultate in terme van biota. Die organiese behandelings, met uitsondering van die ‘vermi-castings’ behandeling, het verhoogte wortel ontwikkeling en -verspreiding in die swaarder grond tot gevolg gehad, Die ‘vermi-castings’ behandeling het ‘n besondere goeie wortelomgewing geskep en ‘n verbetering in die wortelstelsel om ‘n goeie opbrengs en kwaliteit te behaal, was nie nodig nie. Daarinteen het die geotekstiel behandeling beter resultate in die meer sanderige grond behaal. Die geotekstiel behandeling het ook die laagste onkruidstand in beide persele gehad. Opbrengs, in die swaarder grond, en die voorkoms van sonbrand in beide persele, is beïnvloed deur die dekgewasse. In die swaarder grondperseel het die houtspaanders behandeling die hoogste opbrengs getoon en die kompos behandeling, konstant die hoogste voorkoms van sonbrand. In die ligter, sanderige grondperseel, is die hoogste sonbrand voorkoms gemeet in die kontrole behandeling. Die ‘vermi-castings’ behandeling het die laagste sonbrand voorkoms getoon. Weens die beperkte kwantifisering van die besproeiing in die proef, is die gevolge van besproeiing op verskillende deklae nie ondersoek nie en behoort dit oorweeg te word in toekomstige navorsing.

Doctor of Philosophy (PhD) / The goal of this research was to investigate changes in the physiological properties including firmness, stiffness, weight, background colour, ethylene production and respiration of ‘Cripps Pink’ apple stored under different temperature and atmosphere conditions,. This research also seeks to establish mathematical models for the prediction of changes in firmness and stiffness of the apple during normal atmosphere (NA) storage. Experiments were conducted to determine the quality changes in ‘Cripps Pink’ apple under three sets of storage conditions. The first set of storage conditions consisted of NA storage at 0oC, 2.5oC, 5oC, 10oC, 20oC and 30oC. In the second set of conditions the apples were placed in NA cold storage at 0oC for 61 days, followed by NA storage at the aforementioned six temperatures. The third set of conditions consisted of controlled atmosphere (CA) (2 kPa O2 : 1 kPa CO2) at 0oC storage for 102 days followed by NA storage at the six temperatures mentioned previously. The firmness, stiffness, weight loss, skin colour, ethylene and carbon dioxide production of the apples were monitored at specific time intervals during storage. Firmness was measured using a HortPlus Quick Measure Penetrometer (HortPlus Ltd, Hawke Bat, New Zealand); stiffness was measured using a commercial acoustic firmness sensor-AFS (AWETA, Nootdorp, The Netherlands). Experimental data analysis was performed using the GraphPad Prism 4.03, 2005 software package. The Least-Squares method and iterative non-linear regression were used to model and simulate changes in firmness and stiffness in GraphPad Prism 4.03, 2005 and DataFit 8.1, 2005 softwares. The experimental results indicated that the firmness and stiffness of ‘Cripps Pink’ apple stored in NA decreased with increases in temperature and time. Under NA, the softening pattern was tri-phasic for apples stored at 0oC, 2.5oC and 5oC for firmness, and at 0oC and 2.5oC for stiffness. However, there were only two softening phases for apples stored at higher temperatures. NA at 0oC, 2.5oC and 5oC improved skin background colour and extended the storage ability of apples compared to higher temperatures. CA during the first stage of storage better maintained the firmness and stiffness of the apples. However, it reduced subsequent ethylene and carbon dioxide (CO2) production after removal from storage. Steep increases in ethylene and CO2 production coincided with rapid softening in the fruit flesh and yellowing of the skin background colour, under NA conditions. The exponential decay model was the best model for predicting changes in the firmness, stiffness and keeping quality of the apples. The exponential decay model satisfied the biochemical theory of softening in the apple, and had the highest fitness to the experimental data collected over the wide range of temperatures. The softening rate increased exponentially with storage temperature complying with the Arrhenius equation. Therefore a combination of the exponential decay model with the Arrhenius equation was found to best characterise the softening process and to predict changes in the firmness and stiffness of apples stored at different temperatures in NA conditions.

Doctor of Philosophy (PhD) / The goal of this research was to investigate changes in the physiological properties including firmness, stiffness, weight, background colour, ethylene production and respiration of ‘Cripps Pink’ apple stored under different temperature and atmosphere conditions,. This research also seeks to establish mathematical models for the prediction of changes in firmness and stiffness of the apple during normal atmosphere (NA) storage. Experiments were conducted to determine the quality changes in ‘Cripps Pink’ apple under three sets of storage conditions. The first set of storage conditions consisted of NA storage at 0oC, 2.5oC, 5oC, 10oC, 20oC and 30oC. In the second set of conditions the apples were placed in NA cold storage at 0oC for 61 days, followed by NA storage at the aforementioned six temperatures. The third set of conditions consisted of controlled atmosphere (CA) (2 kPa O2 : 1 kPa CO2) at 0oC storage for 102 days followed by NA storage at the six temperatures mentioned previously. The firmness, stiffness, weight loss, skin colour, ethylene and carbon dioxide production of the apples were monitored at specific time intervals during storage. Firmness was measured using a HortPlus Quick Measure Penetrometer (HortPlus Ltd, Hawke Bat, New Zealand); stiffness was measured using a commercial acoustic firmness sensor-AFS (AWETA, Nootdorp, The Netherlands). Experimental data analysis was performed using the GraphPad Prism 4.03, 2005 software package. The Least-Squares method and iterative non-linear regression were used to model and simulate changes in firmness and stiffness in GraphPad Prism 4.03, 2005 and DataFit 8.1, 2005 softwares. The experimental results indicated that the firmness and stiffness of ‘Cripps Pink’ apple stored in NA decreased with increases in temperature and time. Under NA, the softening pattern was tri-phasic for apples stored at 0oC, 2.5oC and 5oC for firmness, and at 0oC and 2.5oC for stiffness. However, there were only two softening phases for apples stored at higher temperatures. NA at 0oC, 2.5oC and 5oC improved skin background colour and extended the storage ability of apples compared to higher temperatures. CA during the first stage of storage better maintained the firmness and stiffness of the apples. However, it reduced subsequent ethylene and carbon dioxide (CO2) production after removal from storage. Steep increases in ethylene and CO2 production coincided with rapid softening in the fruit flesh and yellowing of the skin background colour, under NA conditions. The exponential decay model was the best model for predicting changes in the firmness, stiffness and keeping quality of the apples. The exponential decay model satisfied the biochemical theory of softening in the apple, and had the highest fitness to the experimental data collected over the wide range of temperatures. The softening rate increased exponentially with storage temperature complying with the Arrhenius equation. Therefore a combination of the exponential decay model with the Arrhenius equation was found to best characterise the softening process and to predict changes in the firmness and stiffness of apples stored at different temperatures in NA conditions.