Influence of different organic fertilizers on quality parameters and the delta N-15, delta C-13, delta H-62, delta S-34, and delta O-18 values of orange fruit (Citrus sinensis L. Osbeck)

To investigate the influence of different types of fertilizers on quality parameters, N-containing compounds, and the δ15N, δ13C, δ2H, δ 34S, and δ18O values of citrus fruit, a study was performed on the orange fruit cv. ‘Valencia late’ (Citrus sinensis L. Osbeck), which was harvested in four plots (three organic and one conventional) located on the same farm. The results demonstrated that different types of organic fertilizers containing the same amount of nitrogen did not effect important changes in orange fruit quality parameters. The levels of total N and N-containing compounds such as synephrine in fruit juice were not statistically different among the different treatments. The δ15N values of orange fruit grown under fertilizer derived from animal origin as well as from vegetable compost were statistically higher than those grown with mineral fertilizer. Therefore, δ15N values can be used as an indicator of citrus fertilization management (organic or conventional), because even when applied organic fertilizers are of different origins, the natural abundance of 15N in organic citrus fruit remains higher than in conventional ones. These treatments also did not effect differences in the δ13C, δ2H, δ34S, and δ18O values of fruit.