Influence of three kinds of sewage sludge on the development of olive-rooted cuttings

Abstract

Previous experiments devoted to the study of the agronomic effect of composted sewage sludge application on an olive grove proved, after sixteen months, that the leaves of the Olea europaea L. olive showed some phytotoxic effect. In order to understand the cause, an experiment was carried out on rooted cv. Cornicabra olive cuttings to evaluate the effect of three different types of sewage sludge on specific growth, nutrition and senescence parameters. The experiment took place in a greenhouse. Three treatments were evaluated composted sewage sludge (LC), pruning residues plus composted sewage sludge (RP + LC) and dehydrated sewage sludge thermally dried (LD). Doses studied were 0, 10, 20, 40, 80, and 120 t ha-1. Variables studied were decrease in fresh weight (DPF), variation in stem length (VLT), decrease in root length (DLR), decrease in stem thickness (DGT), final dry weight (PSF), and percentage of total nitrogen (% NT). DPF, VLT, DLR, DGT, PSF, and % NT were evaluated but did not prove significant in terms of RP+LC and LD. Regarding LC, the DPF and %N variables yielded significant responses (p<0.05). The linear regressions obtained were DPF y=-1.70 - 0.0116x, R2 = 0.1471, and % NT y=-1.03 + 0.0033x, R2 = 0.2856, x= rate. Therefore, this test indicates that % NT and DPF, in that order, are the best variables to evaluate the effects of treatment and rate. In general, the rooted olive cuttings were more sensitive to composted sewage sludge treatment. The cause of fitotoxicity was attributed to an electrical conductivity property of 5.6 dSm-1.