Organic Wastes Use in Horticulture: Influences on Nutrient Supply and Apple Tree Growth

The application of fertilizers derived from agroindustrial by-products, represents an interesting opportunity in organic farming. The composition of such inputs includes complex molecules, which strongly influence their effectiveness in providing the optimal nutrient availability and improving crop performances. The aim of the present study was to determine the nutrient release rate of different organic fertilizers and amendments and their effects on shoot growth, fruit production, leaf nutritional status, root biomass and morphology. In a two-years pot trial, two organic fertilizers produced with dried fungal biomass (DFB) and vinasse of sugar beet pulp (VN) and two amendments obtained from fermented animal sewage (SE) and composted olive husks plus grapevine waste (OG), were applied on apple rooted cuttings. One set of plant were not fertilised and acted as Control. The application of DFB, VN and SE increased nitrogen concentration in the soil and in the leaves, supported higher fruit number and enhanced plant growth above and below ground compared to OG and Control. The effect on root growth was positively correlated with nitrogen mineralization rate. For OG treatment, soil electric conductivity negatively influenced root branching frequency, indicating a potential risk of stress due to salinity excess.