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MATERIALS AND METHODS
At two UK sites: site 1 at ADAS Gleadthorpe, Central England and site 2 at IGER North
Wyke, south west England, N 2
O and NH 3
emissions were monitored from replicated
(x 4) plots (6 x 10 m) after a spring (February/March) application of solid manure. The
plots were established on cereal stubble on a loamy sand soil (site 1) and on bare
arable ground on a coarse sandy loam soil (site 2). Cattle farm yard manure (FYM), pig
FYM, layer manure or broiler litter were spread at a target application rate of 250 kg
N/ha and either left on the surface or immediately incorporated (to 20–25 cm depth)
by ploughing. Control treatments were included where no manure was added.
Measurements of N 2
O were made from two static flux chambers (40 cm wide x 40 cm
long x 25 cm high), that were placed in random positions on each plot after the
incorporation treatment had been completed. Chambers were pushed into the soil
up to a depth of 5 cm to ensure an airtight seal and headspace samples analysed
as soon as possible after collection by gas chromatography. The N 2
O flux was
calculated based on the linear increase in N 2
O concentration inside the chamber
over a 40-minute enclosure period. Nitrous oxide emission measurements were
carried out immediately after manure application and at regular intervals over a c.
60-day period.
Ammonia emissions were monitored for up to 2 weeks after manure application
using a modified wind tunnel technique (one per plot) based on the design of Lockyer
(1984). Each wind tunnel consisted of two parts; a transparent polycarbonate canopy
(2.0 x 0.5 m) which covered the plot area, and a stainless-steel duct housing a
fan which drew air through the canopy at a speed of 1 m/s. A sub-sample of the
air entering and leaving the tunnel was drawn through flasks containing 0.02 M
orthophosphoric acid, which absorbed NH 3
present in the air stream. The acid was
subsequently analysed for ammonium-N concentration by automated colorimetry.
The NH 3
emission was calculated as the product of air that flowed through the tunnel
and the difference between the concentrations of NH 3
in the air entering and leaving
the tunnel.
RESULTS AND DISCUSSION
Ploughing reduced mean NH3 emissions (P < 0.001) by 97-98%, with losses from
the ploughed treatments at –0.3% and 0.4% of total-N applied compared with losses
of 15.5% and 19.0% of total-N applied from the plots where manure was left on the
surface. However, at site 1 ploughing increased N 2
O losses (P < 0.001) compared
with those from surface application (Figure 1). Mean N 2
O losses from the ploughed
treatments were a factor of 4´ larger at 1.39% of total-N applied compared with losses
of 0.36% of total-N applied from the plots where manure was left on the surface. In
contrast, at site 2, there was no effect of incorporation on N 2
O emissions (P > 0.05),
although there was a suggestion that ploughing reduced N 2
O losses compared with
surface application. Losses were 0.54% of total-N applied and 1.44% of total-N
applied from ploughed and surface applied treatments respectively. The discrepancy
in the effect of ploughing on N 2
O emissions between sites is probably related to
differences in soil conditions.
The mean soil temperature (5-cm depth) over the monitoring period at site 2 was
10.7ºC with 19% of the mean daily temperatures 8ºC or less. At site 1, the mean
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