Nitrogen fertilization and chemical thinning with 6-benzyladenine affect fruit set and quality of golden delicious apples

The same traits of the apple tree and fruit are affected both by N fertilization and thinning, thus it is assumed that these two factors may interact. Nutrition may be a significant factor influencing fruit size and tree vigor, which may further affect the result of thinning with bioregulators. The objective of this research was to determine the effects of chemical thinning with 6-benzyladenine and N fertilization, as well as their interaction in relation to the yield and fruit quality of apple cv. Golden Delicious. Two N fertilization rates of 30 and 60 kg N ha−1and three thinning treatments with 6-benzyladenine at the rates of 100, 150 and 200 μL L−1within each fertilization plot were applied, including controls. Fruit thinning with BA decreased fruit set and showed significant interaction with N applications. In the presence of excess N supply, higher thinning chemical rates are needed in order to obtain a satisfactory level of thinning. A moderate amount of N fertilizer and thinning with 150 μL L−1 BA provides the highest average fruit weight of Golden Delicious. Intensive thinning in combination with excessive N supply in the soil may delay fruit maturity, which, together with a decrease in fruit firmness, leads to poorer storage ability. When deciding about the BA rate for thinning apple fruitlets, N regime should be taken into consideration, because the same thinning treatment accompanied with an excessive N supply might lead to a weak thinning response, smaller fruit weight, some advanced maturity and poorer storage ability.

► Different N and BA rates were applied in order to determine their interaction.
► At the excessive N supply, higher BA rates should be used to adequately thin fruits.
► 30 kg N ha−1 and thinning with 150 μL L−1 BA provides the highest fruit weight.
► Fruit maturity was delayed and firmness decreased by N fertilization and thinning.