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Zero hunger

How to close nutrient cycles for future Zero Hunger (PICO and Communication session)

EUROSOIL2020CONT-2252

EFFECTS OF RECYCLED FERTILIZERS ON NITROUS OXIDE EMISSIONS IN ORGANIC FARMING

Norah Efosa^{* 1, 2}, Hans-Martin Krause², Roman Hüppi¹, Nadège Vaucher³, Johan Six¹, Else K. Bünemann²

¹Sustainable Agroecosystems, ETH Zurich, ²Soil Sciences, FiBL Research Institute of Organic Agriculture, ³École polytechnique fédérale de Lausanne, Switzerland

Content: Arable agricultural practice contributes to greenhouse gas emissions such as nitrous oxide due to excess N that is not taken up by crops. The recycling of organic waste in biogas plants is proposed as a measure to close nutrient cycles and possible reduce greenhouse gas emissions. It allows the simultaneous generation of energy and organic fertilizers (digestate) which are permitted in Swiss organic farming. The effect of digestate-application on soil-borne nitrous oxide emissions is not yet fully understood but the knowledge is needed in order to optimize fertilizer management. We hypothesize that enhanced nutrient use efficiency of recycling fertilizers reduces nitrous oxide emissions though reduced N availability for soil microbial, nitrous oxide producing processes such as nitrification and denitrification. In this project, digested and un-digested organic fertilizers are applied in a 2.5-years field experiment with three consecutive arable crops (maize, winter wheat and winter barley) under organic farming. We aim to quantify the emissions of nitrous oxide from the application of digestate compared to aerobic manure. Additionally, key factors driving nitrous oxide emissions are identified in order to evaluate mitigation strategies. Results from the first two years of the study suggest a strong control of nitrous oxide emissions by nitrate and ammonia concentrations in the soil. Due to the unusually wet and warm spring followed by a summer drought in Europe in 2018, the influence of nitrate and ammonia on nitrous oxide emissions has been offset by a stronger impact of soil temperature and soil moisture. Nitrous oxide emissions were considerably higher in 2018 during maize cultivation compared to 2019 during winter wheat cultivation despite similar input amounts of fertilizer nutrients. Nitrous oxide emission did not differ between digestate and aerobic manure or mineral fertilizer. The results point out that adaptive strategies in fertilizer management should consider reduced nitrogen inputs in warmer years.

Disclosure of Interest: None Declared

Keywords: Biogas digestate, Global warming, Greenhouse gas, Nitrous oxide