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MATERIALS AND METHODS
Cattle slurry was applied to a clay loam textured grassland soil in Cheshire using
broadcast and shallow injection application techniques in November 2003, and
broadcast and trailing shoe application techniques in March 2004. Slurry was applied
at five application rates (20, 35, 50, 65 and 80 m 3 /ha), with each treatment replicated
three times. Each plot was 6 m wide x 12 m long, and was arranged in a randomised
block design. Slurry was applied using a specialist plot applicator (Plate 1, Basford
et al., 1996), which was representative of commercial practice, with the slots/bands
20 cm apart. Ammonia emissions were measured from each plot for 7 days after
application, using wind tunnels (Plate 1) based on the design of Lockyer (1984). The
depth of the injection slots (after slurry injection) and width of the slurry bands (after
both the shallow injected and trailing shoe slurry application) were measured, and
visual assessments were made of the time taken for the slurry to infiltrate into the
soil.
Plate 1:
Shallow injection slurry application using specialist plot applicator
(left) and measurement of NH 3 emissions with wind tunnels (right)
RESULTS AND DISCUSSION
In November 2003, shallow injection reduced (P < 0.001) NH 3
emissions by an overall
mean of 59% compared with surface broadcast application (Figure 1). The cattle
slurry (5.2% dry matter, 3.1 kg/m 3 total N) was effectively retained in the 7–8 cm
deep injection slots at the application rates between 20 and 50 m 3 /ha (c. 20% soil
surface occupied by slurry), although there was some ‘overspill’ of the injection slots
at the two higher application rates (65 and 80 m 3 /ha; 25–30% soil surface occupied
by slurry). Ammonia emissions were equivalent to a mean of 14% of the total N
applied (range 10–18%) from the broadcast application and a mean of 6% of the
total N applied (range 3–7%) from the shallow injected application. The reduction
in NH 3
emissions achieved by the shallow injection technique reflected the smaller
emitting surface area compared with the surface broadcast applications. There was
no relationship (P > 0.05) between broadcast or shallow injected slurry application
rates and NH 3
emissions in November 2003.
In March 2004, the trailing shoe application did not reduce NH 3
emissions compared
with the surface broadcast application, even though the high dry matter slurry (8.9%
dry matter) remained in a band, covering 18% of the soil surface area at 20 m 3 /ha
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