Sustainable and bioactive substrates to enhance nutrient delivery in soilless production systems

Soilless production systems are widely used in urban farming for food production. Conventional growth media in such systems act as physical support for seed germination and crop growth. However, delivery of nutrients is passive and untargeted, resulting in unnecessary pollution and wastage. Additionally, most of these solid growth media are non-biodegradable and result in excessive sold wastes after crop harvest. Our team has developed a novel growth media using nature-derived biopolymers - keratin and cellulose. These biopolymers can be upcycled from biowastes such as huma hair, poultry feathers and plant wastes from wood shavings, vegetable trimmings etc. A freeze-drying method was employed to fabricate porous growth media with only water as the solvent. The resultant keratin-cellulose growth media are highly porous, have excellent water uptake ability and mechanical resilience. Keratins in the growth media allow binding of cationic micronutrients such as Cu, Zn and Mg via coordination bond, thereby functioning as a reservoir for their controlled release. Furthermore, the growth media fully biodegrade in the operational environment, and provide further nutritional boost through the release of amino acids from the keratins. In addition to the keratin-cellulose growth media, our team has also developed carbon dots (CDs) from sustainable plant wastes as nutrient and agrichemical carriers in urban farming. CDs have been proven to enhance crop growth by enhancing photosynthesis. We further doped metal ions such as Fe, Cu and Zn to the CDs to render them as effective carriers of essential micronutrients for promoting photosynthesis, strengthen plant immunity and fortify nutrients. These metal ions-doped CDs were shown to be efficiently incorporated into the keratin-cellulose growth media to provide a customizable platform for nutrient delivery in soilless production systems. Functional experiments using model plant Arabidopsis and crops such as alfalfa, bok choy and arugula indicate that our growing media act as a nutrient delivery platform that can enhance seedling development and nutrient fortification in soilless production systems. Overall, this study demonstrated the potential of novel approaches derived from composite materials upcycled from biowastes, for the controlled release of nutrients and agrichemicals in soilless production systems. Through further optimization and field tests, we hope to provide a sustainable and practical solution for targeted nutrient delivery to crops, while reducing farm wastes, nutrients wastage and pollution.