S09 - Session O4 - Preliminary results on N2O emission factor calculation in hydroponic Struvite fertilization of lettuce production

Authors: Xavier Gabarrell Durany, Verónica Arcas Pilz *, Gaia Stringari, Ramiro Gonzalez, Gara Villalba

Introduction: In recent years the use of wastewater precipitate struvite (NH4MgPO4·6H2O) as slow-release fertilizer in soil-based agriculture has gained a lot of interest recycle P and reduce losses into the environment. Recent work has revealed the great potential of struvite in hydroponic agriculture as well as the reduction of P emissions into leachate water. However, the nitrogen form in struvite is ammonium, which, when released, can undergo processes of nitrification and denitrification through the bacteria present in the substrate. The present work aims to determine the N 2 O emission factor of struvite in hydroponic production compared to synthetic NO 3 fertilizer. Methodology: For the determination of the GHG N 2 O the chosen methodology is the closed chamber in the ICTA-UAB. The closed chamber split in half through an inner wall provides space for 16 1L plant pots with perlite substrate on each side with a total volume of 2,64m3 (1.32m3 respectively). Each side of the closed chamber is equipped with sensors for temperature, radiation, and humidity as well as an inlet for a vacuum sampler. Each side is planted with lettuce ( Lactuca sativa ). One side is fertilized with a full nutrient solution and the other with a N,P- free nutrient solution. Chamber closing periods were chosen for pre and post air sampling into airtight 1-L bags for each side. Samples were analyzed with gas chromatograph and the HP-PLOT-Q injected manually with an airtight Pressure-Lok Syringe. Results and discussion: The preliminary results have shown low emissions of N 2 O in hydroponic production systems compared to soil-based agriculture. Although close to atmospheric concentrations great amounts of struvite fertilization can lead to higher emitted concentration. Further work is necessary to calculate the environmental footprint of nitrogen fertilization in the form of struvite in hydroponic agriculture.