Novel biobased nitrogen fertilizers - Risks of nitrogen losses, agronomic performance & effects on soil quality
Creators: name: Wester-Larsen, Lærke
Publisher: name: Department of Plant and Environmental Sciences, Faculty of Science, University of Copenhagen
Year: 2024
Subjects: nutrient recycling
biobased

description: PhD thesis by Lærke Wester-Larsen (2024)

SummaryThe agricultural sector is currently facing the challenges of reducing climate and environmental impacts, like all other sectors. Biobased fertilizers (BBFs), produced from organic waste and side-streams, could be one of the means to tackle this challenge by recycling otherwise wasted nutrients and substituting mineral fertilizers. Lately, political interest in recycling nutrients, in a circular economy context, has been increasing. Moreover, the commercial BBFs market is growing and many novel BBFs are now being introduced. However, little knowledge exists on the pros and cons of using these novel BBFs. The aim of this PhD research project was therefore to investigate novel BBFs as a substitute for mineral nitrogen (N) fertilizers and i) Evaluate the main N loss risks from the use of BBFs ii) determine the agronomic performance of field crops fertilized with BBFs and iii) evaluate the effect of BBF application on soil quality.The environmental risks of using BBFs were assessed in a laboratory study (study I) investigating the ammonia (NH3) volatilization risk. The NH3 volatilization risk was found to vary greatly among BBFs both regarding temporal patterns and the accumulated amount of NH3 volatilized. It was affected by soil type and the incorporation of BBFs into soil effectively reduced the NH3 volatilization risk. A laboratory study conducted by Pedersen (2021) assessing the nitrous oxide (N2O) fluxes from the application of BBFs to soil showed a higher emission of N2O from BBFs compared to mineral N (NH4NO3) fertilizer. The N leaching risk was assessed from soil mineral N (sum of NH4+ and NO3-) content (0-90 cm) 18 days after harvest in a field trial (study II). The soil mineral N content indicated that BBFs do not have a higher risk of N leaching than mineral N (NH4NO3) fertilizer.The agronomic performance of BBFs was assessed in field trials at different European sites (study II). The study found that most of the BBFs performed equally well as the mineral N fertilizer reference. A tendency of a second year residual fertilization effect, higher than the mineral reference, was found for some BBFs at some sites, though it was not significant. However, the performance of individual BBFs was not consistent across sites and years. No good explanations were found for this inconsistency. In a comparison of BBFs with more traditional organic fertilizers, e.g. manures, with the same source materials, the BBFs generally had a higher agronomic performance.Biobased fertilizer effects on soil quality were assessed in a laboratory study simulating long-term application (study III). The study showed that BBFs had a neutral to improving effect on soil quality indicators overall when compared to mineral N (NH4NO3) fertilizer. Soil quality was improved to the greatest extent by the compost (BVC), followed by the plant-based (PAL) and the digestate (SDG).In conclusion, BBFs overall seem to be promising substitutes for mineral N fertilizers. However, the underlying mechanisms determining BBF behavior were not fully uncovered. Thus, more research is needed, particularly regarding the controlling factors for the agronomic performance of BBFs.