Nutrient management has a decisive impact on the biomass and essential oil yield of medicinal plants. This study aimed to determine the optimal levels of nitrogen, potassium, and seaweed extract fertilizers to maximize the yield and quality of thyme using the response surface methodology (RSM). The experiment was laid out as a Box-Behnken design with three replications and three experimental factors, including nitrogen (urea) (0, 200, and 400 kg ha⁻¹), and foliar application of potassium (Flourish Sulfopotash) (0, 6, and 12 kg ha⁻¹) and seaweed extract (0, 3, and 6 L ha⁻¹⁾. The generated models were statistically significant for all measured traits except for γ-terpinene and p-cymene. While the influence of N on the amount of photosynthetic pigments followed a quadratic trend, the response of total chlorophyll and carotenoids to increasing potassium was linear. The response of biomass yield to N and seaweed was quadratic and linear, respectively. Potassium application had no significant influence on biomass. Essential oil yield reached its peak value (12 kg ha⁻¹) when N and seaweed were applied at their intermediate levels and with the maximum application rate of potassium. Thymol was identified as the highest essential oil component (46.1%), followed by γ-terpinene (19.2%), p-cymene (14.1%), and carvacrol (5.6%). The optimization results suggested that the application of 162 kg ha⁻¹ urea, 12 kg ha⁻¹ Flourish Sulfopotash, and 4 L ha⁻¹ seaweed extract was sufficient to produce the maximum dry matter (1247 kg ha⁻¹), and more than 11 kg ha⁻¹ of essential oil, with a concentration of 1%. Through optimization, the amounts of thymol and carvacrol were estimated to be as much as 44.2% and 6.2%, respectively. The results of the study suggested that resource optimization through RSM can be used as an efficient method to manage the consumption of fertilizers in thyme production.

Camelina [Camelina sativa (L.) Crantz] is an annual versatile oilseed crop of the Brassicaceae family, with an increasingly cultivated area. Predicting camelina seed yield response to fertilization and planting density is of great importance in understanding production potential and management planning. Therefore, the current study aimed to estimate the seed yield of camelina by response surface methodology (RSM) and artificial neural network (ANN) as affected by different levels of planting row spacing and nitrogen (N), sulfur (S), and cow manure (CM) fertilization. The experiment was conducted in two growing years of 2019–2020 and 2020–2021, based on a central composite design with four factors including row spacing (15–35 cm), N (0–200 kg ha⁻¹), S (0–100 kg ha⁻¹), and CM (0–40 t ha⁻¹). The RSM models for seed yield versus fertilization and row spacing factors in both years were statistically significant and had an acceptable predictive ability. Camelina seed yield decreased with increasing row spacing but showed a positive response to increasing the amount of N, S, and CM fertilizers. Comparing the performance of the models showed that, although the RSM models were significant and had the necessary efficiency in predicting camelina seed yield, the ANN models were more accurate. The performance criteria of coefficient of determination (R²), root mean square error (RMSE), standard error of prediction (SEP), mean absolute error (MAE), and Akaike information criterion (AICc) averaged over the two years for the RSM model were 0.924, 51.60, 5.51, 41.14, and 394.05, respectively, and for the ANN model were 0.968, 32.62, 3.54, 19.55, and 351.33, respectively. Based on the results, the ANN modeling can be used in predicting camelina seed yield in field conditions with more confidence than the RSM technique.

Three harvest stages including one-stage (one time after 36 days), two-stage (two times, every 18 days) and three-stage were considered in order to evaluate the effect of gradual harvest of oleoresin on essential oil quantity and quality of male and female Pistacia atlantica Subsp. Kurdica. The results demonstrated that essential oil percentage was not affected by genders and treatments. Limonene in male gender and o-Cymene in female gender were more in comparison with each other. Moreover, α-pinene in harvesting of two-stage was lower than other times. Furthermore, 4,8-epoxy-para-mentyh-1-ene in male gender as well as β-cyclocitral in female gender only found in the harvesting of one-stage, while other compounds found in the essential oil were not affected by different stages of gradual harvest.