Quantity and quality of production, partitioning of dry matter and of mineral nutrients in apple trees subjected to four-year different fertilization strategies

This four-year trial (2011-2014), carried out in Northeastern Italy on ‘Red Delicious’ Sandidge/M9 trained to spindle, was made to determine which kind of fertilization strategy can improve productivity and quality and to test the effect of nutritional strategies on the development of the different organs and the distribution of nutrients in the plant. The trial refers the comparison of four different nutritional strategies, based on the total amount of 70 kg of nitrogen (N) with a control. Five different treatments, replicated three times, were compared: unfertilized test (T) or control, distribution of fertilizers by radical way, split in autumn-spring (AS), exclusive spring application (S), fertigation (F), and combination of radical spring fertilizer and fertigation (SF). In each growing season, physiological data (SPAD, NDVI), nutrient content of leaves and fruits, production, and quality were measured. In order to check nutritional modifications due to fertilization, after the harvest in 2014, three plants per treatment were excavated. Successively they were divided into different annual or permanent organs. T produced less, with smaller and shorter fruits than the other treatments, but with the highest color. F had significantly higher yields than T and AS. The treatments S, F, and SF, had plants with higher levels of SPAD, NDVI and leaf N and also had more vigorous and productive plants, with hard, acidic fruits, and less sugar content and color compared with T and AS. Plants subjected to fertilization had a significant greater number of fine roots and leaf area than unfertilized ones. The distribution of the nutrients in the plant in relation to fertilization application indicated significant differences in total accumulation/plant for N, phosphorus (P), potassium (K), and sulfur. Fertigation was more efficient than soil application, excluding for iron (Fe) in roots and leaves, and calcium (Ca) in fruit