Organic waste compost and spent mushroom compost as potential growing media components for the sustainable production of microgreens

Abstract

Microgreens are emerging specialty crops becoming increasingly popular for their rich nutrient profile and variety of colors, flavors, and textures. The growing medium is a significant key factor in microgreen yield, quality, and sustainability. The widespread use of peat-based media raises questions regarding the environmental sustainability of microgreens production, and new substrates that are more sustainable are required. To this purpose, a study was designed with the objective of comparing eight alternative growing media evaluating their physicochemical properties and effect on yield, mineral profile, and nutritional quality of peas and radish microgreens. Tested substrates included a standard peat and perlite mixture (PP), coconut coir (CC), spent mushroom compost (SMC), organic waste compost (CMP), and 50:50 (v:v) mixes of PP and SMC, PP and CMP, CC and SMC, and CC and CMP. The physicochemical properties widely differed among the alternative substrates tested. SMC had high electrical conductivity and salt concentration, which resulted in poor seed germination. Growing media tested significantly influenced the production and nutritional quality of both microgreen species and variations were modulated by the species. With a 39.8% fresh yield increase or a small yield decrease (-14.9%) in radish and peas, respectively, PP+CMP (50:50, v/v) mix provided microgreens of similar or higher nutritional quality than PP, suggesting the potential of substituting at least in part peat with CMP. Using locally available CMP in mix with PP could reduce the microgreens industry reliance on peat while reducing costs and improving the sustainability of the production of microgreens. Further research is needed to evaluate also the potential economic and environmental benefits of using locally available organic materials like CMP as alternative growing media and peat-substitute to produce microgreens.

Yield performance, mineral profile, and nitrate content in a selection of seventeen microgreen species

“…Examining the content of Mn and Cu, their content was consistent with the range of concentrations observed by Xiao et al (2016) and Di Gioia et al (2019a) in Brassicaceae species, while Kyriacou et al (2021a) reported much higher Mn content for four Brassica rapa L. microgreens. For sunflower, Poudel et al (2023b) reported values of Mn and Cu slightly lower than those observed in the present study on a DW basis. On the other hand, Corrado et al (2021) reported higher levels of Mn and much lower levels of Cu in borage microgreens compared to the levels observed in this study.…”

“…Boron content was on average 0.34 mg 100 g -1 FW and ranged between a minimum of 0.08 mg 100 g -1 FW in borage and a maximum of 0.18 mg 100 g -1 FW in lemon balm microgreens, except for scallion microgreens that had a much higher B content (0.37 mg 100 g -1 FW) compared to all the other species. Very limited information is available in the literature on the variation of B content in microgreens, but in the case of sunflower, similar levels were observed by Poudel et al (2023b) in sunflower shoots derived from untreated seeds. Conversely, D'Imperio et al ( 2021) observed B levels nearly three times higher in mizuna microgreens grown in peat and fertilized with half-strength Hoagland nutrient solution.…”

Radish microgreens produced without substrate in a vertical multi-layered growing unit are rich in nutritional metabolites

“…In line with the dietary recommendation and society’s increasing interest in healthy eating, there has been an increase in demand for fresh, functional, and nutraceutical foods while still being delicious ( Kyriacou et al., 2016 ). Microgreens, with their diverse range of colors, flavors, and textures along with their rich nutrient profile, are gaining popularity as emerging specialty crops ( Poudel et al., 2023 ).…”

“…The time from seeding to harvest is crop dependent and may vary from one to three weeks ( Di Gioia et al., 2017 ). Based on their age or size during harvesting and consumption, sprouted seeds can be categorized as sprouts (youngest and shortest), microgreens (intermediate, about 2 inches tall and harvested within 7-14 d), and baby greens (oldest and largest, 3-4 inch tall) ( Kou et al., 2014 ; Poudel et al., 2023 ). A widely accepted definition of microgreens is “Tender immature greens produced from seeds of vegetables and herbs having fully developed cotyledons with or without the emergence of a rudimentary pair of first true leaves” ( Xiao et al., 2012 ; Senevirathne et al., 2019 ).…”

“…A widely accepted definition of microgreens is “Tender immature greens produced from seeds of vegetables and herbs having fully developed cotyledons with or without the emergence of a rudimentary pair of first true leaves” ( Xiao et al., 2012 ; Senevirathne et al., 2019 ). Microgreens have special qualities such as rich flavor, unique color, and concentrated bioactive compounds, which could make them a choice to garnish a wide range of main dishes or to improve the sensory qualities of salads ( Kou et al., 2014 ; Treadwell et al., 2020 ; Poudel et al., 2023 ). As a result, they regarded as “functional foods”, which have capabilities that go beyond simply providing nutrients to health-promoting or disease-preventing properties ( Xiao et al., 2012 ).…”