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soil temperature was 9.3ºC, but with 41% of the mean daily temperatures ≤ 8ºC.
Site 2 was wetter than site 1 with twice as much rain (174.4 mm) falling over the N 2
O
monitoring period compared with site 1 (85.8 mm). Numerous studies in the literature
have shown that N 2
O production increases with temperature and can be stimulated
with a rise in soil moisture (Dobbie et al., 1999; Scott et al., 2000). Ploughing is likely
to increase the length of the diffusion pathway from the site of N 2
O production (the
FYM) to the soil surface. Soil texture and structure would influence this diffusion
rate. So at site 2, although conditions were more favourable for N 2
O production than
at site 1, the rate of N 2
O diffusion through the soil was probably slower due to the
heavier textured and wetter soil. This would provide a greater opportunity for N 2
O
reduction to N 2
and hence lower N 2
O emissions.
Later work from this project at a site with a clay soil in central England has shown
similar results to those at site 2. Despite no effect of ploughing (P > 0.05) on N 2
O losses
calculated over c. 60 days, surface application resulted in mean losses 4x larger than
from ploughing. Evidence from the literature also indicates an uncertain effect of
ploughing/simulated incorporation of solid/liquid manures such that, depending on
site conditions, the impact on N 2
O may be neutral, or result in enhanced or reduced
emissions (Velthof et al., 2003; Thorman et al., 2005a, b).
Figure 1: Total N 2
O emission (% total-N applied) calculated over c. 60 days
after application of solid manure to cereal stubble (site 1) and bare
arable ground (site 2) in spring. CM, cattle manure; PM, pig manure;
LM, layer manure; BL, broiler litter; surf, surface application; plo,
plough. Error bars represent ± one standard error of the mean
CONCLUSIONS
This study shows that the effect of rapid incorporation by ploughing on N 2
O loss was
inconsistent. In the wet, south west ploughing had no effect on N 2
O emissions, but
at the drier, central site N 2
O losses increased, suggesting that rapid incorporation by
ploughing as a best management practice for NH 3
abatement may only be used as a
‘win–win’ technique under site specific conditions.
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