Evaluating recycling fertilizers for tomato cultivation in hydroponics, and their impact on greenhouse gas emissions

Abstract

Soilless culture systems offer an environmentally friendly and resource-efficient alternative to traditional cultivation systems fitting within the scheme of a circular economy. The objective of this research was to examine the sustainable integration of recycling fertilizers in hydroponic cultivation—creating a nutrient cycling concept for horticultural cultivation. Using the nutrient film technique (NFT), three recycling-based fertilizer variants were tested against standard synthetic mineral fertilization as the control, with 11 tomato plants ( Solanum lycopersicum L. cv. Pannovy) per replicate ( n = 4) and treatment: two nitrified urine-based fertilizers differing in ammonium/nitrate ratio (NH ₄ ⁺:NO ₃ ⁻), namely (1) “Aurin” (AUR) and (2) “Crop” (CRO); as well as (3) an organo-mineral mixture of struvite and vinasse (S+V); and (4) a control (NPK). The closed chamber method was adapted for gas fluxes (N ₂O, CH ₄, and CO ₂) from the root zone. There was no indication in differences of the total shoot biomass fresh matter and uptake of N, P and K between recycling fertilizers and the control. Marketable fruit yield was comparable between NPK, CRO and S+V, whereas lower yields occurred in AUR. The higher NH ₄ ⁺:NO ₃ ⁻ of AUR was associated with an increased susceptibility of blossom-end-rot, likely due to reduced uptake and translocation of Ca. Highest sugar concentration was found in S+V, which may have been influenced by the presence of organic acids in vinasse. N ₂O emissions were highest in S+V, which corresponded to our hypothesis that N ₂O emissions positively correlate with organic-C input by the fertilizer amendments. Remaining treatments showed barely detectable GHG emissions. A nitrified urine with a low NH ₄ ⁺:NO ₃ ^– (e.g., CRO) has a high potential as recycling fertilizer in NFT systems for tomato cultivation, and S+V proved to supply sufficient P and K for adequate growth and yield. Alternative cultivation strategies may complement the composition of AUR.

Electronic supplementary material

The online version of this article (10.1007/s11356-020-10461-4) contains supplementary material, which is available to authorized users.