The root environment as influenced by mulches, on two different soil types and the resulting effect on fruit yield and sunburn of 'Cripps' Pink' apples

Nicholson, Allison Frances (2012-12)

Thesis (MScAgric)--Stellenbosch University, 2012.

Thesis

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.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/71960
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