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Nutrient management on intensive dairy farms in the southwest of Ireland
Humphreys, James Tracey, Mark McNamara, Kevin
Humphreys, James
Tracey, Mark
McNamara, Kevin
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2006-08-01
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Humphreys, J., Tracey, M., McNamara, K. Nutrient management on intensive dairy farms in the southwest of Ireland, End of Project Reports, Teagasc, 2006.
Abstract
Intensive grass-based dairy farming relies on high inputs of nutrients that are now regulated under
SI 378, 2006 (Good Agricultural Practice for Protection of Waters). This project studied nutrient
management practices on twenty-one intensive dairy farms in the south-west of Ireland between
2003 and 2006. Mean stocking rate was 202 kg organic-N/ha deposited by grazing livestock.
Overall fertiliser-N use on the farms decreased from 266 to 223 kg N/ha/yr during the study, with
the rate of fertiliser-N in the first application each year decreasing from 49 to 33 kg N/ha, while
the rate of fertiliser-N applied for first cut silage production also fell from 106 to 96 kg N/ha.
These decreases were partly achieved by applying more slurry in springtime and by the
introduction of white clover on five of the farms. While the limits on fertiliser-N use under SI 378
were exceeded on ten farms in 2003, the limits were exceeded on only two farms in 2006.
Fertiliser-P usage declined from 12.0 to 10.2 kg P/ha/yr, and complied with the limits of SI 378
on thirteen of the farms in 2006. Mean Morgan’s extractable soil P concentration (STP) exceeded
10 mg/l on five farms, while the mean concentration exceeded 8 mg/l on ten farms. Phosphorus
management, therefore, was close to that required by SI 378 on most farms. Slurry storage
capacity met or exceeded the minimum requirements of SI 378 on eight farms; substantial
investment in slurry storage facilities was necessary on thirteen farms. The mean N surplus on the
farms declined from 277 to 232 kg N/ha/yr during the study due to a decline in total N input from
335 to 288 kg N/ha/yr over the same period. The mean efficiency of N-use increased from 17.9 to
20.2 %. The large variation in rates of fertiliser-N applied on farms with similar stocking rates
suggests potential for further improvements in N use efficiency on some farms. Decreases in
nutrient input levels can be partly attributed to increased farmer awareness, due to advice and
record keeping from this study and the introduction of SI 378, and the increasing cost of nutrient
inputs relative to output prices. In terms of fertiliser N and P use and soil P concentrations,
complying with the limits in SI 378 does not require major changes in nutrient management
practices on the majority of these intensive dairy farms.