COMPOST FROM FRESH ORANGE WASTE: A SUITABLE SUBSTRATE FOR NURSERY AND FIELD CROPS

Composting represents a valuable strategy for recycling orange processing waste for use as soil conditioner, provided compost maturity is duly evaluated. Following a 5-month aerobic bioconversion, orange waste reached an acceptable degree of maturity in terms of humification parameters, absence of phytotoxicity (determined on test plants according to ISO methods) and low content of simple phenolic compounds. A greenhouse experiment with two nursery crops (tomato and zucchini) showed that, depending on the characteristics of the growing substrate (vermiculite or perlite), orange compost addition selectively induced pH and electrical conductivity (EC) increases, which in turn would affect plant growth responses. In field crops shoot mass weight was increased after compost addition. Results suggest that at field scale, orange compost may be used for organic fertilization; while in nursery crops it can be mixed with commercial potting substrates selected in relation to plant sensitivity. In horticultural crops, for its greater ability to buffer pH and EC changes, vermiculite could represent the preferred complementary substrate compared to perlite.