Re-use of industrial orange wastes as organic fertilizers

The aim of this study was to evaluate the possibility of the re-use of industrial orange wastes as organic soil fertilizer. The assay was performed with a lettuce variety widely produced and consumed in Portugal and, consequently, with great commercial interest. Lactuca sativa L. (osteolata variety) was cultivated in Mitcherlich pots containing samples of a poor soil of the Algarve region. This soil was prepared with different amounts of either pulp or peel orange-wastes from an orange-juice industry. The wastes were applied according to an increasing amount of nitrogen. The results obtained were submitted to statistical tests, in order to find the relations between the production of fresh and dry matter, and the percentages of nutrients (nitrogen, phosphorous, potassium, calcium, magnesium and iron) that were obtained in the dry matter, with the types and amounts of wastes applied. An increase in the average production of both fresh- and dry-matter with increasing amounts of either pulp or peel wastes applied, and high positive correlation coefficients between the average percentages of nitrogen, phosphorus and potassium obtained in the dry matter with the average production of both fresh- and dry-matter were found. No phytotoxicity was observed.