Effects of Organic Fertilization on Soil Organic Matter and Root Morphology and Density of Orange Trees

The aim of this work was to verify the effect of organic fertilization on soil organic matter and on root apparatus of adult 'Valencia late' citrus trees [Citrus sinensis (L) Osbeck], grafted on C. aurantium L., in a citrus orchard (Sicily, Italy) organically managed from 15 years. In a randomized block experimental design, compost from pastazzo (a mixture of citrus pulp and peel), poultry manure, bovine manure, compared to a mineral fertilizer, was applied to the soil (455 g N/plant/year). For each plant, the same volume (0.022 m(3)) of soil was sampled at the same distance from the trunk for determination of root density (root weight/soil volume). Representative young roots were selected and analyzed by electron scanning microscopy (SEM). As far as soil characterization concerns, TOC, TEC, HA and FA were determined and then the related humufication parameters (HR% and DH%) were calculated. Results showed that organic fertilization, when compared to the mineral one, determines not only an improvement of soil organic matter humification, but also an increase of root biomass in citrus trees. The SEM analysis evidenced that organic fertilizers induce the appearance of adventitious buds on the terminal portions of the roots, a higher regularity of the elongating meristematic cells and, also, an increase of the production of root mucigel, thus improving their potential ability to up take nutrients from soil.