7. N₂O Emissions and Inorganic N Release Following Incorporation of Crop Residue and/ or Inorganic N Fertiliser into Soil

Abstract

Nitrous oxide emissions are usually increased following incorporation of crop residues or inorganic N fertiliser into soil, but the effect of combining these inputs at different proportions on N dynamics and NO emissions has 2 yet to be adequately examined. The interactive effect of combining crop residues barley (Hordereum vulgare) and clover (Trifolium pretense) and inorganic N fertiliser (NH₄NO₃) on N₂O emission and mineral N dynamics under controlled laboratory conditions is reported. Emissions of NO were significantly higher from soils amended with 2 the low C:N ratio clover residues compared to the high C:N ratio barley residue treatments and was further increased, following combined application of crop residues and inorganic N fertiliser. Furthermore, the magnitude of emission was influenced by the proportions at which the residue-N and the fertiliser-N were combined with the 75:25 fertiliser:clover treatment emitting the highest (P < 0.05) amount of 65 mgN₂O-N m^-2 30 d^-1. Incorporation of sole clover residues resulted in net N mineralization and addition of sole barley residues led to a net N immobilization. However, combined application of either residue with inorganic N fertiliser resulted in netNmineralisation. The results from the study demonstrated that whilst there is the potential for N₂O emission to be controlled through varying ratios of residue:fertiliser input, the magnitude and direction of interactions between these N sources vary between different species as a result of their different qualities. This relationship should be verified under field conditions.