Organic and chemical N fertilization on coriander (Coriandrum sativum L.)

Coriander (Coriandrum sativum L.) is an annual herbaceous Medicinal and Aromatic Plant (MAP) dealing with a great industrial interest because of its strongly-scented fruits (“seeds”). The role of N fertilization in coriander seed yield is matter of debate as far; information is missing, for instance, about the effects of organic N fertilization, a mandatory technique when the organic cropping management is chosen. Organic and chemical N fertilizers have been supplied on coriander from 2001–2002 to 2006–2007 in a Mediterranean semi-arid environment, and their effects on the formation of biomass and seeds yield have been evaluated. Different organic fertilizers, allowed by EU regulations concerning organic agriculture,were compared with a chemical fertilizer (urea = N 46%), and with an untreated test. All conventional fertilizers were applied in three arrangements: 80 kg ha−1 at sowing; 40 kg ha−1at sowing + 40 kg ha−1 top-dressed; 80 kg ha−1 at sowing + 40 kg ha−1 top-dressed. Data were collected about straw yield, seeds yield and plant parameters (including number of umbels per plant, number of seeds per umbel, and mass of 100 seeds), and then they were submitted to ANOVA, Correlation analysis and Multiple Regression analysis. Seed yields showed a strong variability between years, and the rainfall amount measured from plant emergence to the start of flowering (ST1) stage showed a tight linkage to yields; in particular, a rainfall amount lower than 100 mm between crop emergence and ST1 stage may explain the low average seed yields in the three lower-yielding years. The environmental conditions exerted a strong effect on the efficiency of N use, and when rainfall was too low, the effectiveness of N supply was sharply reduced.Chemically-derived N supply improved seed yields and yield-forming traits more N from organic source. Some beneficial effect on yields was observed after the application of certain organic N fertilizers containing significant amounts of P, that would require further specific studies. No difference was found when the same N amount was applied in a single basal application or in two applications during the season.Regression analysis proved to be a useful tool to individuate the direct and indirect effects of the observed yield parameters on seed and straw yield. The MRA allowed the highlighting of the diversified response of coriander to the different fertilization management strategies. It also highlighted the importance of the harvest index and the total cycle duration, which was not revealed by the previous ANOVA results.