Quantifying the effect of commercial nitrogen formulations BlackUrea™ / BlackDAP™ as alternative nitrogen source on fruit tree physiology, yield and fruit quality of two apple cultivars

Janse van Vuuren, Liaan (2018-03)

Thesis (MScAgric)--Stellenbosch University, 2018.

Thesis

ENGLISH ABSTRACT: The relationship between plant and soil is very complex and understanding it is fundamental to optimal use of fertilizers for a profitable yield, without compromising the environment. Nitrogen (N) fertilizers plays an important role in ensuring high-quality apples while sustaining high yields. N fertilizer products face challenges regarding loss of efficacy due to leaching and volatility. Understanding the mode of action of the available commercial N formulations is necessary to maximize the efficiency of N applications under different environmental conditions. To determine the effect of applied N, three commercial N fertilizer formulations: BlackUrea™, BlackDAP™ and UreaHB, were applied as the only N source on ‘Rosy Glow’ and ‘Golden Delicious’ cultivars, on sandy loam soils in Ceres, South Africa. Different parameters, including physiological and vegetative measurements, were recorded to determine the effect of different N formulations after soil applications on three dedicated phenological stages. The reaction of root growth dynamics on the different N formulations were also studied in the ‘Rosy Glow’ orchard. Lastly, the use of satellite imaging (FruitLook®) to quantify the effect N formulations on biomass and N levels in trees was evaluated on the ‘Golden Delicious’ orchard. The results from this study proved that urea could be used as an alternative N source to other ammonium formulations, under these conditions, without any negative effects on fruit quality or yield, during this short-term study of two seasons. However, the potential acidification of urea as only N source over time has been reported under different conditions and needs to be considered. No significant (ns) differences were reported between treatments in the ‘Rosy Glow’ trial, which may partly be due to the cultivar choice. Nevertheless, the positive trend in an increase in yield with the BlackUrea™ treatment compared to UreaHB in the ‘Rosy Glow’ was confirmed in an increase (ns) in yield after one season of application in the ‘Golden Delicious’ trial. White root growth showed differences between treatments in the ‘Rosy Glow’ trial. UreaHB and BlackDAP™ treatments had more white roots compared to BlackUrea™ which had a more evenly distributed white root count. This did not affect the leaf N concentrations or other vegetative parameters during the two seasons but indicated an effect of formulation. A pot trial with tomatoes showed contrasting results compared to those in the apples, with more growth (ns) and higher leaching of ammonium and nitrates in the BlackUrea™ than UreaHB treatment. This may be partly due to the effect of the coating of the BlackUrea™ that underperformed under conditions of high irrigation and inert sand as medium. FruitLook® was able to identify differences in biomass and N levels between treatments, providing accurate additional information of treatments in addition to field measurements, derived from spectral data.

AFRIKAANSE OPSOMMING: Die verhouding tussen plante en grond is baie kompleks en ‘n goeie begrip daaroor is van kardinale belang vir die optimale gebruik van kunsmis vir ‘n winsgewende opbrengs, sonder om die omgewing te benadeel. Stikstof (N) bemesting speel ‘n belangrike rol in die verbouing van hoë kwaliteit appels en handhawing van ‘n volhoubare hoë opbrengs. Die gebruik van N kunsmis produkte het sekere uitdagings weens die verlies van N via loging en vervlugtiging. ‘n Begrip van die wyse van werking van beskikbare kommersiële N formulasies is noodsaaklik om die effektiwiteit van N toedienings onder verskillende omgewingstoestande te optimiseer. Ten einde die effek van die toegediende N kunsmis te bepaal, is drie kommersiële N kunsmis formulasies: BlackUrea™, BlackDAP™ and UreaHB, as enkel N bron toegedien op ‘Rosy Glow’ en ‘Golden Delicious’ kultivars, op ‘n sandleem grond in Ceres, Suid Afrika. Verskillende parameters, insluitende vegetatiewe en fisiologiese metings, is bestudeer om die effek van die verskillende N formulasies as grondtoedieinings op drie fenonolgiese stadia, te kwantifiseer. Die reaksie van wortel groei dinamika op die verskillende N formulasies is ook bestudeer in die ‘Rosy Glow’ boord. Laastens is die gebruik van satelliet beelde (FruitLook®) ingespan om die effek van N formulasies op biomassa en N vlakke in die bome te kwantifiseer in die ‘Golden Delicious’ boord. Resultate van die studie het bewys dat onder hierdie omstandighede, ureum as alternatiewe N bron, gebruik kan word sonder negatiewe effekte op vrug kwaliteit of opbrengs, oor die kort tydperk van twee seisoene. Die potensiaal van ureum om as enigste N bron oor tyd tot versuring van grond onder ander omstandighede te lei moet in gedagte gehou word. Geen betekenisvolle verskille tussen behandelings is gevind in die ‘Rosy Glow’ proef nie. Dit mag gedeeltelik te wyte wees aan die kultivar keuse. Desnieteenstaande is die positiewe tendens in toename in opbrengs met die BlackUrea™ behandeling teenoor die UreaHB in die ‘Rosy Glow’ proef bevestig met ‘n nie-betekenisvolle toename in opbrengs na een seisoen se toediening in die ‘Golden Delicious’ proef. Witwortelgroei het verskille getoon tussen behandelings in die ‘Rosy Glow’ proef. Die UreaHB en BlackDAP™ behandelings het meer wit wortels in vergelyking met die BlackUrea™ behandeling wat meer gelyke verspreiding van witwortels getoon het. Dit het geen effek gehad op die blaar N konsentrasies of ander vegetatiewe parameters gedurende die twee seisoene nie, maar daar is aanduidings van ‘n moontlike formulasie effek. ‘n Potproef met tamaties het kontrasterende resultate met die van die appels getoon, beter groei (nb) en ‘n meer loging van ammonium en nitrate in diewas verkry by die BlackUrea™ behandelings versus UreaHB. Dit kan gedeeltelik toegeskryf word aan die effek van die BlackUrea™ wat onderpresteer het in die omgewing van hoë besproeiingsfrekwensies en die inerte sandmedium. FruitLook® was in staat om verskille in biomassa en N vlakke tussen behandelings te kwantifiseer vanaf spektrale data en daardeur akkurate asook addisionele inligting rakende die behandelings toe te voeg wat nie deur veldmetings gekwantifiseer was nie.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/103574
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