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£25,000. The investment in trailing hose application equipment was assumed
necessary to allow the pig slurry to be applied evenly to growing crops without
causing soil compaction and crop damage. The annual amortised repayment cost
was £3,500 for the extra slurry storage capacity (over 20 years) and £3,250 for the
improved application equipment (over 10 years). Changing the slurry application
timing from autumn to spring increased the slurry fertiliser N replacement value (by
reducing N leaching losses) of the pig slurry by £180 on the Cambridgeshire farm and
£380/year on the East Yorkshire farm. Also, the fertiliser saving by reducing ammonia
emissions through the use of bandspreading equipment was equivalent to £230 per
year on both farms. Hence, the net annual cost of changing the slurry application
timing from autumn to spring was £6,340 on the Cambridgeshire farm and £6,140 on
the East Yorkshire farm. The costs of abating nitrate loss were equivalent to £14.09
and £6.46/kg of nitrate-N saved on the Cambridgeshire and East Yorkshire farms,
respectively. The cost of abating ammonia loss was £5.60/kg of ammonia-N saved
(Table 2).
Cattle Slurry
After autumn cattle slurry applications, estimated nitrate leaching losses were 1,890 kg
N (i.e. 6,300 kg slurry N x 30% of total N applied) on the Devon farm, 1,070 kg N
(6,300 kg slurry N x 17% of total N applied) on the Shropshire farm and 690 kg N
(6,300 kg slurry N x 11% of total N applied) on the North Yorkshire farm (Table 2). The
differences in nitrate losses between the model farms largely reflected differences in
rainfall volumes (Table 1) and to a lesser extent seasonal differences in grass growth
and drainage volumes. Ammonia emissions from the surface broadcast applications
were estimated at 2,720 kg (18% of N applied), compared with 1,900 kg from the
bandspread applications (30% reduction compared with surface broadcasting).
At all three farms, the capital investment costs of increasing slurry storage from 3
to 6 months (2,100m 3 to 4,200m 3 ) were £73,500 and the capital costs of purchasing
a tanker and trailing shoe machine were £25,000. The investment in trailing shoe
application equipment will increase the number of days slurry can be spread without
causing soil compaction and sward damage, and will reduce sward contamination.
The annual amortised repayment cost was £5,880 (over 20 years) for the increased
storage capacity and £3,250 (over 10 years) for the improved spreading equipment.
The value of the nitrogen saved (through reduced N leaching losses) by changing the
application timing from autumn to spring was £760/year on the Devon Farm, £430/
year on the Shropshire Farm and £280/year on the North Yorkshire farm. The saving
in ammonia loss from bandspread slurry application on the three farms was £330/
year. The net costs of changing application timing practices from autumn surface
broadcast spreading to spring bandspreading were £8,040, £8,370 and £8,520/year
on the Devon, Shropshire and North Yorkshire farms, respectively. The costs of
abating nitrate loss were equivalent to £4.25, £7.85, £12.35/kg of nitrate-N saved on
the Devon, Shropshire and North Yorkshire farms, respectively. The cost of abating
ammonia loss was £3.96/kg of ammonia-N saved on all three farms.
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