Epsilon Archive for Student Projects

Abstract

To meet the increasing global food demand sustainably, the establishment of a circular
bioeconomy is imperative. Transforming biowaste into valuable amendments has gained
significant attention as a crucial step towards achieving a circular bioeconomy. However, to fully
optimize the potential of biowaste-based amendments, it is essential to determine the most
beneficial products for specific plants under specific growing conditions. These benefits extend
beyond soil amendment and nutrient provision, as compounds within the organic fraction of the
amendments can enhance plant performance through various means beyond nutrient supply.
Nonetheless, limited comparative analyses have been conducted on even the most common
organic amendments derived from biowaste conversion. Hence, this study has three objectives.
The first objective is to compare the effects of organic amendments on plant development, growth,
and photosynthetic efficiency. The evaluation includes six biowastes and their conversions: (i)
anaerobic digestate from manure and vegetable waste, (ii) vermicompost from vegetable waste,
(iii) frass of yellow mealworm from wheat bran and potato leftovers, (iv) frass of black soldier fly
fed on vegetable waste, and (v-vi) vegetable waste mixed with phytotoxic olive pomace in two
different amounts; (vii) heat-precipitated brown juice from alfalfa, and (viii) acid-precipitated
brown juice from alfalfa. The performance of plants treated with these amendments is compared to
plants grown without any amendment (negative control) and those fertilized with an ammonium�based Hewitt solution (positive control). All plants, except the negative control, received the same
amount of nitrogen, phosphorous, and potassium, adjusted to the same pH, and were irrigated to
the same water retention capacity. The second objective is to investigate the safety of frass from
black soldier fly larvae fed on phytotoxic olive pomace in varying quantities. The third and final
objective is to explore the interactions between anaerobic digestate and frass of yellow mealworm
when used together as amendments, focusing on their combined impact on plant performance. The
thesis provides an overview of the concept of plant biostimulants, their relevant categories, the
conversion processes of biowaste into organic amendments, and their potential biostimulant
effects. Secondly, the amendments are characterized, and the effects of their application in a
greenhouse trial on pak choi are reported, including plant growth, development, and leaf-level
photosynthetic efficiency measurements. It is observed that frass produced by black soldier fly
larvae fed on olive pomace exhibits phytotoxic properties. Unexpected phytotoxicity or deficiency
associated with the frass masks the interactions between anaerobic digestate and yellow mealworm
frass. The initial biostimulatory effects of vermicompost and anaerobic digestate disappear after 20
days of growth. None of the amendments demonstrate a positive effect on the final fresh biomass
of pak choi after 50 days of growth, which cannot be attributed solely to nutrition. Several
potential limitations in the experimental design are identified, cautioning the interpretation of the
findings, and emphasizing the need for further experiments under more suitable conditions to
confirm the absence of biostimulant effects. Nonetheless, we can suggest anaerobic digestate as
the most promising among the organic amendments studied.