Seed Density, Fertilizer Concentration, Temperature, and Substrate Depth Effect on Three Microgreen Species of the Brassicaceae Family

Microgreens are a young, tender and edible crop harvested shortly after emergence of the first true leaf. To date, insufficient published data exists on the influence of cultivation practices on plant yield, morphology and nutritional composition of microgreens. The objective of this research is to determine the effects of varying seeding densities, fertilizer concentrations, ambient air temperatures and substrate depths on the growth of microgreens. Four experiments were conducted to independently determine the influence of seeding density (1.1, 1.65, 2.2, 2.75 and 3.3 seeds/cm²), fertilizer rate (0, 50, 100, 150 and 200 ppm N) at each irrigation, aerial temperature (14, 18, 20 and 22 °C) from germination to harvest and substrate depth (1.8, 3.3, 4.3 and 5.8cm). Trials were conducted using three species, mizuna (Brassica rapa), arugula (Eruca sativa) and mustard ‘Garnet Giant’ (Brassica juncea) in a glass greenhouse in Ithaca, NY with temperature trials between the months of December and January. Measured parameters included fresh weight (FW), plant height and dry weight (DW). Results were analyzed using linear and quadratic regression. Each experiment had between 8 and 12 replicates per treatment combination with a total of 3 experimental replications over time. For temperature trials, FW increased linearly for all three species as temperature increased from 14 to 20°C with little to no further FW gain at 22°C. Seed density trials showed that for all three species, FW increased in a significant quadratic fashion as seed density increased from 1.1 to 3.3 seeds/cm² with diminishing FW above 2.75 seeds/cm². In the analysis of varying substrate depths, arugula FW increased linearly as substrate depth increased from 1.8 to 5.8 cm. Mizuna was best fit by a quadratic regression with FW increasing as substrate depth increased from 1.8 to 5.8 cm. Evaluation of basic cultivation practices on the growth of these emerging crops is an important first step in the progression of research surrounding their cultivation. Based our findings, good performance of the three species in this trial can be obtained at a seed density of 2.75 seeds/cm², an aerial temperature between 20 and 22°C and a substrate depth of 5.8cm. Further research is underway to evaluate the effects of varying daily light integral (DLI) and CO₂ enrichment on the growth and nutritional characteristics of microgreens.