New Zealand Journal of Agricultural Research abstracts
Calculating nitrogen leaching losses and critical nitrogen application rates in
dairy pasture systems using a semi-empirical model
H. J. DI
K. C. CAMERON
Soil, Plant and Ecological Sciences Division
P.O. Box 84
Lincoln University
Canterbury, New Zealand
Abstract A simple, semi-empirical model for estimating
nitrogen (N) leaching losses and critical N application rates in dairy pasture
systems is described. The model uses the annual rates of major N flux processes
in the soil-plant system to determine the potentially leachable N pool (mineral
N and mineralisable N), and estimates the N leaching loss based on measured
relationships between the N leaching loss and the potentially leachable N in
the soil. The N flux processes considered in the model include fertiliser or
effluent N applications, biological N fixation, soil N mineralisation and
immobilisation, plant N uptake, animal N return at the urine patches, ammonium
volatilisation, and denitrification. The impact of drainage on N leaching is
taken into account by normalising the N leaching loss to a per 100 mm drainage
basis. A quadratic equation is used to describe the relationship between the N
leaching loss and potentially leachable N. Tests of the model predictions
against other experimental data showed reasonable agreements between the
estimated N leaching losses with those measured. The modelled critical N
application rates which would cause the annual average N concentration in the
drainage water to reach the drinking water standard (11.3 mg N l-1)
are: 390-392 kg N ha-1 for cut and carry, and 162-192 kg N
ha-1 for grazed pastures if urea is used; and 588-600 kg N
ha-1 for cut and carry, and 248-301 kg N ha-1 for grazed
pastures if dairy shed effluent is used.
Keywords nitrate; cycling; urine; urea; effluent; water
quality; modelling
New Zealand Journal of Agricultural Research, 2000, Vol. 43: 139-147
0028-8233/00/4301-00139 $7.00/0 (c) The Royal Society of New Zealand
2000
PDF file of entire paper: medium quality (716K); (scanned from paper original: notes about this process)
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