Utilization of derivatives from nutrient recovery processes as alternatives for fossil-based mineral fertilizers in commercial greenhouse production of Lactuca sativa L.

Abstract

The production of vegetables relies on the use of mineral fertilizers which are based either on fossil fuel (e.g., nitrogen fertilizers based on Haber–Bosch process) or on fossil ore deposits (phosphate rock). On the other hand, nutrient recovery processes generate various end and side products that can provide a sustainable alternative for fossil-based mineral fertilizers. Their use however, is currently limited by insufficient knowledge about the properties and the impact of these products on soil quality and crop yield. This research was aimed to evaluate the use of the liquid fraction of digestate, effluent from constructed wetlands originating from a manure/digestate treatment facility, air scrubber water and struvite in the cultivation of lettuce (Lactuca sativa L.) compared to their conventional fossil-based counterparts. In accordance with the crop nutrient requirements, different fertilization treatments were set up in which individual products and combinations were tested. At harvest time, assessment of soil physicochemical properties was conducted, along with crop quality control. Nutrient balances were determined and an economic and environmental assessment was evaluated. There were no significant differences in crop yield and soil quality at harvest time between conventional fossil-based mineral fertilizers and selected bio-based mineral alternatives. Nitrogen and potassium use efficiencies were slightly lower in treatments with bio-based fertilizers. Moreover, economic and ecological assessment have shown higher benefits for the farmer when bio-based alternatives were used as a replacement for synthetic fertilizers. Re-use of these products should be stimulated in European legislation.