New Zealand Journal of Agricultural Research abstracts
An analysis of environmental and economic implications of nil and restricted
grazing systems designed to reduce nitrate leaching from New Zealand dairy
farms. I. Nitrogen losses
C. A. M. DE KLEIN
AgResearch
Invermay Agricultural Centre
Private Bag 50 034
Mosgiel, New Zealand
S. F. LEDGARD
AgResearch
Ruakura Research Centre
Private Bag 3123
Hamilton, New Zealand
Abstract Nitrate leaching is perceived to be a serious
consequence of dairy farming due to the uneven return of N in small
concentrated urine patches. Management systems in which the direct deposition
of urine is avoided throughout the year (nil grazing) or during autumn/winter
when the risk of nitrate leaching is highest (restricted grazing) could
potentially reduce nitrate leaching. However, possible disadvantages of such
systems include a reduction in the clover content of pastures, increases in
gaseous losses, and increases in capital and/or operating costs. This paper
examines some of the effects of nil and restricted grazing management systems
for dairy farming on N flows and losses to the environment. The estimates of N
losses are based on the results of a long-term farmlet study under conventional
grazing, on data for an average New Zealand farm, and on literature
information. The analysis showed that in nil grazing systems nitrate leaching
losses may be reduced by 55-65% compared with conventional grazing systems, and
by 35-50% in restricted grazing systems. For nil grazing systems, however,
total N losses were 10-35% higher than under conventional grazing because of
increased gaseous losses. The total N losses from restricted grazing systems
were similar (-10 to +5%) to those from conventional systems. The analysis
showed the potential benefit of a restricted grazing system as a management
tool to reduce nitrate leaching losses, especially in areas where contamination
of ground and surface waters is of particular concern.
Keywords analysis; dairying; nitrate leaching; grazing
management; nitrogen losses
New Zealand Journal of Agricultural Research, 2001, Vol. 44: 201-215
0028-8233/01/4402&3-0201 $7.00/0 (c) The Royal Society of New Zealand
2001
PDF file of entire paper: medium quality (1209K); (scanned from paper original: notes about this process)
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