Download as a PDF - CiteSeerX

the cost of these financial investments will be partly offset by increased manure
fertiliser N replacement values (resulting from reduced nitrate and ammonia losses)
and increased spreading opportunities for slurry throughout the cropping season.
Plate 1:
Trailing hose slurry application to winter wheat (left) and trailing
shoe slurry application on grassland (right)
This paper quantifies the economic implications of changing manure management
practices to minimise nitrate leaching and ammonia volatilisation losses on model
pig, dairy and broiler farms on contrasting soil types and under different climatic
conditions.
MATERIALS AND METHODS
The impacts of changing manure application timings from autumn (August–October)
to spring/summer (February–July) on nitrate leaching losses and ammonia emissions
were quantified for six model livestock farms (Table 1). The amount of nitrogen applied
to land was estimated based on standard livestock N production figures (Anon,
2000). For the dairy farms, it was assumed that 60% of the estimated N production
was spread as slurry, with the remainder deposited during spring/summer grazing.
For the pig and broiler farms, it was assumed that all of the estimated N production
was returned to land via manure applications.
N Losses
Data from experiments carried out on a range of soil types (Chambers et al., 2000;
Williams et al., 2005a), where nitrate leaching losses were measured after autumn
surface broadcast applications of slurry or broiler litter, were used to estimate nitrate
leaching losses as a percentage of the total N applied. Ammonia emissions were
estimated using MANNER (Chambers et al., 1999) assuming a slurry dry matter
content of 4% for pig slurry and 6% for cattle slurry. Slurry bandspreading was
assumed to reduce ammonia losses by 30% compared with surface broadcasting
(Chambers et al., 2001).
Storage Capacity and Spreading Equipment
The existing slurry storage capacity was assumed to be 3 months for the model dairy
farms and 4 months for the model pig farms, which is typical of current commercial
practice (Smith et al., 2000, 2001). On the dairy farms, it was assumed that slurry
could be spread in spring from early February to late March and to silage aftermaths
in the summer (i.e. an August to January no spread period). To avoid the need to
85