When urine and fertiliser were deposited concurrently prior to
winter drainage, the fertiliser-N made a negligible contribution to
the total inorganic-N leaching pool with <2.17% of the 15N applied
as fertiliser recovered in the leachate after 554 days. These results
conflict with the commonly held belief that fertiliser applied over a
urine patch will simply exacerbate the fertiliser’s contribution to
the NO3
-N leaching load because the N supplied from the urine patch is already surplus to the pasture’s N requirements. We
therefore disprove the first hypothesis that, increased fertiliser
associated leaching would occur under urine patches with
increasing rates of fertiliser applied. However, it is important to
note that at the highest annual N application rate of 400 kg Nha1,
which is double the recommended best practice rate, split N
fertiliser applications on top of a urine patch increased the total
NO3
leaching loss (i.e. from non-fertiliser N sources). We
confirmed the second hypothesis, that leaching would be greatest
under an autumn deposited urine patch when compared to a
spring deposited urine patch. The results of this study indicate that
best practice fertiliser management (i.e. fertiliser applied at
<200 kg Nha1 year1) is environmentally benign under the
current experimental conditions, even in a wetter than average
year.
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