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RSM modeling of nitrogen use efficiency, biomass and essential oil of Salvia officinalis L. as affected by fertilization and plant density

Abstract Introducing optimum ranges of agronomic resources such as fertilizers and plant materials is of great importance in crop production systems. In this study response surface methodology (RSM) was used for empirical modeling and optimizing the effects of plant density, nitrogen (N) and micronutrients (M) fertilizers on dry matter yield, essential oil production and nitrogen use efficiency (NUE) of sage (Salvia officinalis L.). The experimental factors of plant density (5–10 plants m−2), N (0–200 kg ha−1) and M (0–4 g L−1) fertilizers were laid out in a Box-Behnken design. Increasing plant density under high rates of M fertilizer resulted in increased dry matter, essential oil and NUE while plant density without M fertilizer application, had no effect. The simultaneous application of N and M fertilizers had a synergistic effect on dry matter yield and essential oil production. In general NUE decreased with increasing the rate of N fertilizer. Through optimization operation the density range of 8.7–10 plants m−2, the N fertilizer rate less than 95 kg ha−1 and the M fertilizer range of 2.4–4 g L−1 were suggested as the optimum conditions to obtain desirable values of responses.