Effect of slurry application techniques on nitrous oxide emission from temperate grassland under varying soil and climatic conditions

The effect of slurry application techniques and slurry N stabilizing strategies on nitrous oxide emission from grasslands is poorly understood and, therefore, can result in large uncertainties in national/regional inventories. Field experiments were, thus, conducted to estimate the effect of different fertilization techniques on nitrous oxide (N2O) emissions. Fertilizer was applied (135-270 kg N ha(-1) year(-1)) as calcium ammonium nitrate (CAN), untreated or treated cattle slurry. The slurry was either treated with sulfuric acid (target pH = 6.0), applied using trailing shoes or treated with 3,4-dimethyl pyrazole phosphate and applied via slot injection. N2O fluxes were sampled using the closed chamber technique. Cumulative N2O emissions ranged 0.1-2.9 kg N ha(-1) year(-1) across the treatment, sites and years. The N application techniques showed inconsistent effects on soil mineral N content, cumulative N2O emission and N yield. The fertilizer replacement value of slurry was low due to low N use efficiencies at the sites. However, a close positive relationship (r = 0.5; p = .013) between slurry value and biomass yield was observed, highlighting the benefit of high slurry value on crop productivity. N2O-N emission factors were low for all treatments, including CAN, but were 2-6 times higher in 2019 than in 2020 due to lower precipitation in 2020. Variations in N2O emission were largely explained by soil and climatic factors. Even with the low N2O emissions, this study highlights the benefit (significant mitigation of N2O emissions) of replacing the increasingly expensive chemical fertilizer N with input from slurry under favourable conditions for denitrification.