Direct, delayed and residual effects of applied wastewater from olive processing on nitrogen and phosphorus availability in the soil-plant system

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Abstract
The use of wastewater from olive processing as fertilizer was investigated in a greenhouse experiment. Wastewater was applied alone or together with mineral nutrients to pots filled with a calcareous soil. A first sowing with barley, and after fallowing, a second sowing with ryegrass demonstrated, respectively, the direct and delayed effects of the effluent on dry matter yield and the availability of N and P. The direct effect of olive wastewater, especially at high doses, was to reduce all parameters, whereas the opposite effect was seen over time. The joint application of N ameliorated the direct effects of wastewater application, and all mineral complements potentiated, in overall terms, the delayed effects. The final postharvest analysis showed all treatments which contained wastewater to residually raise total N and available P in soil.