Browsing by Author "Janse van Vuuren, Liaan"
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- ItemQuantifying the effect of commercial nitrogen formulations BlackUrea™ / BlackDAP™ as alternative nitrogen source on fruit tree physiology, yield and fruit quality of two apple cultivars(Stellenbosch : Stellenbosch University, 2018-03) Janse van Vuuren, Liaan; Lotze, Elmi; Stander, J.; Stellenbosch University. Faculty of AgriSciences. Dept. of Horticulture.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.