Nutrient Disorder Symptomology and Refining Leaf Tissue Nutrient Standards of Basil (Ocimum basilicum L.)

Basil ( Ocimum basilicum L.) is a popular annual herb grown for culinary, medicinal, and ornamental purposes. Existing foliar nutrient sufficiency ranges for basil are based on field-grown plants, which can vary from the nutritional requirements of crops grown in controlled environments. This prompts the need for refined nutrient fertilizer concentration recommendations and foliar nutrient interpretation ranges that are specific to greenhouse-grown basil. The objectives of this study were to determine critical leaf tissue concentrations when disorders were observed, to evaluate the effects of varying macronutrient fertilizer concentrations on basil growth and yield, and to develop foliar nutrient interpretation ranges for greenhouse-grown basil. Basil ‘Prospera Compact DMR (PL4)’ plants were grown in an automatic recirculating hydroponic system and supplied with a modified Hoagland’s solution. To evaluate varying macronutrient applications, eight different concentrations (0, 8, 16, 32, 64, 100, 200, and 300%) of nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), and sulfur (S) were applied, with all other elements held constant. Similarly, micronutrient deficiencies were induced by individually omitting one element from the nutrient solution per treatment. Deficiency symptoms were photographed for all treatments except copper, manganese, and molybdenum, which did not develop visual deficiency symptoms after 57 days, when the experiment was terminated. Plant tissue was collected to measure the plant dry mass and leaf tissue nutrient concentrations. The effects of varying macronutrient fertilizer concentrations were evaluated by comparing three regression models (linear, quadratic, and quadratic plateau) to determine the foliar concentration of each element corresponding with optimal growth. To develop foliar mineral nutrient interpretation ranges for greenhouse-grown basil, additional foliar tissue analysis data ( n = 1938) from greenhouse-grown basil were obtained and compiled. By expanding upon the sufficiency range approach, foliar nutrient interpretation ranges for deficient, low, sufficient, high, and excessive values were established for the 12 essential elements. For each element, Normal, Gamma, and Weibull distributions were fitted to the data, and the optimal distribution was chosen according to the lowest Bayesian Information Criterion value. The resulting macronutrient concentration recommendations and foliar interpretation ranges are valuable resources that can aid in troubleshooting nutrient disorders and optimizing growth of greenhouse-grown basil.