Impacts of slurry acidification and injection on fertilizer nitrogen fates in grassland

Abstract

Low nitrogen (N) use efficiency of broadcast slurry application leads to nutrient losses, air and water pollution, greenhouse gas emissions and—in particular in a warming climate—to soil N mining. Here we test the alternative slurry acidification and injection techniques for their mitigation potential compared to broadcast spreading in montane grassland. We determined (1) the fate of 15N labelled slurry in the plant-soil-microbe system and soil-atmosphere exchange of greenhouse gases over one fertilization/harvest cycle and (2) assessed the longer-term contribution of fertilizer 15N to soil organic N formation by the end of the growing season. The isotope tracing approach was combined with a space for time climate change experiment. Simulated climate change increased productivity, ecosystem respiration, and net methane uptake irrespective of management, but the generally low N2O fluxes remained unchanged. Compared to the broadcast spreading, slurry acidification showed lowest N losses, thus increased productivity and fertilizer N use efficiency (38% 15N recovery in plant aboveground plant biomass). In contrast, slurry injection showed highest total fertilizer N losses, but increased fertilization-induced soil organic N formation by 9–12 kg N ha−1 season−1. Slurry management effects on N2O and CH4 fluxes remained negligible. In sum, our study shows that the tested alternative slurry application techniques can increase N use efficiency and/or promote soil organic N formation from applied fertilizer to a remarkable extent. However, this is still not sufficient to prevent soil N mining mostly resulting from large plant N exports that even exceed total fertilizer N inputs.

Use of 15N tracers to study nitrogen flows in agro-ecosystems: transformation, losses and plant uptake

“…In grasslands broadcast surface application is the most common application technique for liquid cattle slurry, but involves a range of environmental issues resulting from the low NUE and high N losses induced by this fertilization technique (Zistl- Schlingmann et al 2019Schlingmann et al , 2020. Schreiber et al (2022) used 15 N labeled cattle slurry to study the impacts of slurry acidification and injection on fertilizer nitrogen fates in grassland. They show how alternative slurry application techniques can increase NUE and/or promote soil organic N formation from applied fertilizer to a remarkable extent, but emphasize that the additional refueling of SON stocks promoted by slurry injection is still not sufficient to prevent soil N mining mostly resulting from large plant N exports that even exceed total fertilizer N inputs.…”