Cover crops and soil tillage differently affect N2O emissions

Summary in the original language of the document

Cover crop residues can affect nitrous oxide (N2O) emissions when incorporated, however, effects may differ depending on tillage strategy and cover crop. The objective of this case study was to quantify N2O emissions and investigate how the temporal variability is influenced by tillage strategy and cover crop type . Perennial ryegrass (RG, Lolium perenne), plantain (PL, Plantago lanceolata), RG-PL, and RG-PL-red clover mix (RG-PL-RC, Trifolium pratense) were either terminated by shallow rotovation followed by moldboard ploughing (ro+plou), or directly by ploughing (plou), whereafter spring barley was established. The N2O flux was continuously measured with automated chambers from mid-March until mid-June 2021 (DOY 72-166). During March and April the soil temperature was low and rainfall limited. Rotovation induced residue mineralization and on average 10.9% of cumulative N2O emissions, with emissions of different magnitudes in RG, RG-PL and RG-PL-RC, and no stimulation in PL. Soil NO3--N accumulated from 3.5 to 10.4 and 2.9 to 8.6 mg kg-1 in ro+plou and plou, respectively (DOY 84-119), indicating a predominantly aerobic soil environment during this period. The differences in NO3--N accumulation and reduction rates aligned well with the composition of cover crops. In May there was intense rainfall, and on average 92% of emissions occurred after 1 May. A statistical analysis of the temporal dynamics showed that plou treatments generated more, high-magnitude and short-duration N2O peaks than ro+plou. Overall, cumulative N2O-N emissions were higher for plou (3.6-7.0 kg ha-1) than for ro+plou (1.2-3.8 kg ha-1), with highest and lowest difference in PL and RG-PL-RC, respectively . Irrespective of tillage, RG, PL, and RG-PL had predominantly daytime maximum N2O emissions, while RG-PL-RC had more nighttime maximum N2O emissions. Following ploughing, N2O emissions were significantly related to WFPS indicating that denitrification was the main process behind N2O emissions in this period. The study showed that rotovation prior to ploughing can mitigate N2O emissions, but that this effect is highly dependent on interacting effects of cover crop composition and the soil environment which, therefore, need to be understood and integrated in management strategies for cover crop termination.