Leaf nutrient concentration standards for lemon verbena (Aloysia citrodora Paláu) obtained from field and pot fertilization experiments

Lemon verbena (Aloysia citrodora Paláu) is a perennial shrub native to South America, used in the food industry to add a lemon flavour to food and drink. The species has also caught the attention of the scientific community due to its potential pharmaceutical value. In spite of the useful work that has been carried out in recent years on the chemical composition and pharmacological properties of lemon verbena, very few agronomic studies have been carried out on this crop. There are no studies reporting the elemental composition of this species, making it impossible to monitor crop nutritional status through plant analysis or to establish accurate fertilizer recommendation programs. This work reports results from field and pot fertilization trials that took place in NE Portugal during 2013-2015 to assess crop response to applied N, P, K or B as fertilizers, to establish sufficiency ranges for important macro and micronutrients and SPAD-readings and to estimate crop nutrient removals in aboveground biomass. To this end, a total of 13 fertilizer experiments were conducted which involved 46 cuts of vegetation. Nitrogen fertilization significantly increased dry matter yield of lemon verbena on almost all the sampling dates of the field and pot experiments. In the conditions of these experiments, P and K did not increase dry matter yield of lemon verbena. Crop response to applied B was only found in 2014 on a few sampling dates. The sufficiency ranges set for the macronutrients N, P, K, Ca, and Mg were respectively 28.0-43.0, 0.9-3.8, 10.0-28.0, 7.5-30.0, and 2.0-8.0 g kg−1. The sufficiency ranges found for the micronutrients B, Cu, Fe, Zn, and Mn were, respectively, 35-200, 7-22, 60-300, 25-125, 40-250 g kg−1. Adequate SPAD readings were found within the range 40-45. Aboveground dry biomass removed 31.2, 2.2, 25.3, 16.7, and 4.2 kg t−1, respectively of N, P, K, Ca and Mg.