Co-application of organic amendments and urea-N enhanced CO2 and N2O emissions from a sandy soil; insights of soil N transformations and organic amendments quality.
Authors: Giannopoulos Georgios , Pasvadoglou Elpida , Kourtidis George , Elsgaard Lars , Zanakis George , Anastopoulos Ioannis 
Published: February 2023

Under the framework of Circular Economy, EU Green Deal and UN Sustainable Development Goals the use of organic amendments is highly promoted as a cost-efficient solution to improve soil quality and agrosystem sustainability. Nonetheless, their agronomic use comes with an uncertainty of their potential to release ample plant-available N, and to emit soil greenhouse gasses.We investigated short-term (90 d) soil N dynamics of a sandy soil mesocosms receiving four organic amendments (50 t/ha) (i) cow manure compost (CMC), (ii) food waste compost (FWC), (iii) used digestate substrate (UDS) and (iv) municipal sewage sludge (MSS), without and with N fertilization (200 kg/ha; urea-N). An unamended soil mesocosm was included as control. During the incubation soil NO3-, NH4+, N2O and CO2 were regularly monitored. At the end of the incubation potential N mineralization (AMN), total Kjeldahl N, organic C, and trace-metals were determined.During the incubation, organic amendments increased ~6x soil NO3- availability (AUC) than C, however soils receiving MSS had similar AUC NO3- to the fertilized soils (~13x). Only MSS increased ~5x available soil NH4+ (AUC) relative to unamended soil. Co-application of urea and organic amendments increased AUC NO3- and AUC NH4+ ~5x, relative to the unamended soil. Organic amendments increased cum. N2O emission by 10, 20, 1% and 13x relative to the control, and additional 20% increase when urea was co-applied for CMC, FWC, UDS and MSS, respectively. Similarly, organic amendments increased cum. CO2 emission by 20, 40, 140, and 1% relative to the control, and additional 10% increase when urea was co-applied for CMC, FWC, UDS and MSS, respectively.At the end, total N increased by 37, 23, 80 and 20% relative to the unamended soil, and an additional 20% when urea was co-applied for CMC, FWC, UDS and MSS, respectively. Org. C increased by 30, 20, 4 and 50%, and an additional 7% when urea was co-applied for CMC, FWC, UDS and MSS, respectively. AMN increased 2, 50 and 220% and an additional 20% when urea was co-applied for CMC, FWC and MSS, respectively, whereas no change was observed for soil receiving UDS relative to the control. Treatments receiving MSS without and with N had relatively higher amounts of total Mg, Zn, Mn, Cu and S than the unamended soil, whereas no significant differences in trace-metals were observed for CMC, FWC and UDS treatments.In conclusion, our preliminary results indicate that co-application of organic amendments with urea-N could potentially fuel CO2 and N2O emissions from soils, thus offsetting any favorable aspects of the aforementioned policies. Organic amendment, urea-N and their interaction were significant factors (p&#8804;0.05) driving CO2 and N2O emissions. The quality and composition of the amendments may stimulate soil microbial N transformations, and further investigation will elucidate the intrinsic role of soil microbes and their dynamics regulating CO2 and N2O emissions from soils.The research project was supported by the Hellenic Foundation for Research and Innovation (H.F.R.I.) under the 2nd Call for H.F.R.I. Post-Doctoral Research Projects; #01053 awarded to Dr Georgios Giannopoulos. This project was co-implemented with Corteva Agriscience Hellas SA.&#160;