New Zealand Journal of Agricultural Research abstracts
A lysimeter study of the fate of 15N-labelled nitrogen in
cow urine with or without farm dairy effluent in a grazed dairy pasture soil
under flood irrigation
H. J. Di
K. C. Cameron
R. G. Silva
Centre for Soil and Environmental Quality
P.O. Box 84
Lincoln University
Canterbury, New Zealand
J. M. Russell
J. W. Barnett
Fonterra Research Centre
Private Bag 11 029
Palmerston North, New Zealand
Abstract Nitrate (NO3-) leaching
from cow urine patches is considered to be a major contributor to the overall
NO3- leaching loss in grazed dairy pastures. Farm dairy
effluent (DE) is usually applied to grazed pastures to recycle nutrients.
The objective of this study was to determine the fate of cow urine nitrogen
(N), labelled with 15N, applied to soil monolith lysimeters with
or without DE application. The soil was a Templeton fine sandy loam (Haplustepts),
and the pasture was perennial ryegrass (Lolium perenne) and white
clover (Trifolium repens). Cow urine was applied in the autumn at
1000 kg N ha-1 either alone or with DE (400 kg N ha-1
yr-1 split into four applications). The lysimeters were flood
irrigated. One year after application, 6.4-9.1% of the 15N-labelled
urine N was lost by leaching, 29.3-38.8% was removed in the cut pasture,
45.7-47.5% remained in the soil and plant roots, and <2% was lost by volatilisation.
The application of DE plus urine significantly increased pasture yield and
pasture N offtake above those in the Urine alone treatment, but reduced the
percentage recovery of the 15N-labelled urine N in the pasture
top compared with the Urine alone treatment. The amount of N unaccounted
for was slightly higher in the Urine + DE (13.9%) treatment than in the Urine
alone treatment (5.3%), probably due to increased denitrification as a result
of organic carbon inputs from the DE. The urine N application significantly
suppressed the clover component of the pasture, and this has implications
for N budgeting on grazed dairy pastures. The amount of 15N lost
by leaching from the Urine alone treatment confirms that this is a major
contributor to the overall effect of dairying on drainage water quality.
Keywords nitrate leaching; pasture; dairy; urine;
denitrification; volatilisation
A02013 Received 21 February 2002; accepted 23 September 2002; published
9 December 2002
New Zealand Journal of Agricultural Research, 2002, Vol. 45: 235-244
0028-8233/02/4504-0235 $7.00/0 © The Royal Society of New Zealand
2002
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