Commercial fertilizers and organoleptic quality of organically grown apple fruits (cv Golden delicious)

Summary

In the organic production only organic fertilizers can be used to supply the soil with nitrogen. The mineralization of these products is slow causing a problem with the nitrogen supply when the demands of the plants is high.
Italy is the main producer of organic apples in Europe (about 42,000 MT on 115,000 MT in 2006). More then 60% of the organic apples produced in Italy are grown in Alto Adige region (North-East of Italy). In this region problems with nitrogen supply to apple plants in spring are common. In spring the demand of nitrogen of the apple trees in Alto Adige is high, but the weather conditions are often bad and the temperature of the soil is slow. In these conditions the mineralization of the organic fertilizers starts slowly, the trees own reserves may become exhausted, the nitrogen supply from the mineralization of the soil organic matter is not yet sufficient. Therefore, it is important to supply the plants timely in spring with fertilizer nitrogen.
The objective of this work was to determine the effect of various commercial fertilizers used for organic apple growing and the conditions of their use on the organic acid and sugar composition and on the formation of volatile compounds in fruits of Golden delicious cultivar. The fruits were grown in the experimental fields of the Centro di Sperimentazione Agraria e Forestale Laimburg, in Alto Adige region. In addition, fruits from a plot without the use of fertilizer (“control”) and a plot where a mineral fertilizer (“ammonium sulphate”) were grown in Laimburg, harvested and analyzed for comparison. Malic, oxalic and citric acid were the organic acids detected; fructose, glucose and sucrose the sugars identified and quantified. Higher levels of organic acids and sugars were found in the “control “and “ammonium sulphate” samples. The different conditions of fertilization seemed to significantly affect the formation of some aroma volatile compounds. Considering the three main key odorants, butyl acetate level was higher in the “compost + biogas slurry” sample and in the “control”; a higher level of hexyl acetate was found in the “control” only. For both compounds lower levels were found in the “ammonium sulphate” sample and in one of the organic fertilizer “Azocor 105” treatment. No differences were found in the level of 2-methylbutyl acetate.
Aknowledgement: Work carried out in the project “Qualità nutrizionale ed organolettica e impatto ambientale di produzioni biologiche. Un caso studio: il melo”, funded by Ministero delle Politiche Agricole Alimentari e Forestali