Industrial orange waste as organic fertilizer in durum wheat

Nowadays agro-industrial waste induces increasing problems due to the high economic cost and heavy environmental impact of disposal. By contrast, its potential re-use as organic fertilizer could represent a sustainable approach to recycling nutrients and reintegrating organic matter into soil. Such recycling should be particularly beneficial in Mediterranean areas because there is a progressive loss of soil fertility. To assess the possible re-use of industrial citrus waste as organic fertilizer, a two-year research project was carried out to study the effects of dried orange waste on the growth and production of durum wheat (Triticum durum Desf.). Two dried orange waste doses of 4 and 8 kg/m2 were compared with conventional mineral fertilization, of 80 kg/ha2 of nitrogen, and with a control without fertilization in the first year. During the second year, the residual effects of the past year’s fertilization and two-year application of the orange waste doses and mineral fertilization on duration of biological cycle, grain yield, leaf area index, above-ground biomass and crop growth rate were studied. Our results show that organic fertilization gave similar wheat yields to the mineral fertilization, averaging at 3.63 t/ha. Organic fertilization promoted crop growth much more than mineral fertilization, by up to +400%. However, at the highest dose repeated organic fertilization induced a severe depressive effect on crop establishment. It indeed gave the lowest values for leaf area index of 0.6, biomass of 222 g/m2 dry weight and crop growth rate of 2.5 g m−2 d−1 at the heading stage, and a 50% decrease in wheat grain yield. In both years, the lowest dose of orange waste produced maximum agronomic efficiency. We conclude that an appropriate use of dried orange waste as fertilizer can partially solve environmental problems related to the citrus fruit processing industry, and represents a low cost organic matter source for Mediterranean soil with poor fertility.