Fates of slurry-nitrogen applied to mountain grasslands: the importance of dinitrogen emissions versus plant N uptake.

Unlabelled: Intensive fertilization of grasslands with cattle slurry can cause high environmental nitrogen (N) losses in form of ammonia (NH), nitrous oxide (NO), and nitrate (NO ) leaching. Still, knowledge on short-term fertilizer N partitioning between plants and dinitrogen (N) emissions is lacking. Therefore, we applied highly N-enriched cattle slurry (97 kg N ha) to pre-alpine grassland field mesocosms. We traced the slurry N in the plant-soil system and to denitrification losses (N, NO) over 29 days in high temporal resolution. Gaseous ammonia (NH), N as well NO losses at about 20 kg N ha were observed only within the first 3 days after fertilization and were dominated by NH. Nitrous oxide emissions (0.1 kg N ha) were negligible, while N emissions accounted for 3 kg of fertilizer N ha. The relatively low denitrification losses can be explained by the rapid plant uptake of fertilizer N, particularly from 0-4 cm depth, with plant N uptake exceeding denitrification N losses by an order of magnitude already after 3 days. After 17 days, total aboveground plant N uptake reached 100 kg N ha, with 33% of N derived from the applied N fertilizer. Half of the fertilizer N was found in above and belowground biomass, while at about 25% was recovered in the soil and 25% was lost, mainly in form of gaseous emissions, with minor N leaching. Overall, this study shows that plant N uptake plays a dominant role in controlling denitrification losses at high N application rates in pre-alpine grassland soils.

Supplementary Information: The online version contains supplementary material available at 10.1007/s00374-024-01826-9.