Effect of agro-industry by-products on soil fertility, tree performances and fruit quality in pear (Pyrus communis L.)

Organic materials from agro-industry processes can be used in agriculture as a way to recycle materials that still maintain a high fertilizing value. The aim of the experiment was to evaluate the value of soil applied apple juice by-product as fertilizer for pear trees. A 3-year experiment was carried out in a mature pear orchard (cv Abbé Fétel grafted onto quince MC) in the Po valley (Italy), where the following treatments were compared: 1) unfertilized control; 2) mineral N fertilization (60 kg N ha−1 year−1 split in two spring applications); 3) apple juice by-product (1.3 t ha−1 year−1, equal to 60 kg N ha−1), fully supplied at petal drop; 4) apple juice by-product, at twice the rate of the previous treatment. Apple juice by-product soil decomposition accounted for 12% in the first 6 months. At the end of the 24-month-assay, the decomposition accounted for 24% on total dry weight that makes 28% of initial C and 36% of initial N. Soil nitrate-N concentration was increased by the mineral N fertilizer, while the application of apple juice by-product increased microbial carbon. Tree growth, yield and fruit quality were not affected by treatments, while mineral N fertilization raised leaf and fruit N concentration. In conclusion, in our conditions the use of apple juice by-product did not show negative effects on tree performances and fruit quality, with some advantages related to the recycling of organic wastes in agriculture.