New Zealand Journal of Agricultural Research abstracts

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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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