Nitrogen leaching from dairy farms on volcanic soils under high rainfall and effects of mitigation with gibberellic acid targeted to urine patches using Spikey® technology

<p dir="ltr">Nitrogen (N) leaching from grazed pastures occurs predominantly from animal urine. Several mitigation options have been developed. In this study we investigated application of gibberellic acid directly to urine patches only, after grazings using Spikey® targeted technology. This was tested over three years in two farm studies, near Rotorua and Stratford, on volcanic soils under high rainfall (>2000 mm annually). Previous New Zealand grazing N leaching studies have all been in low-medium rainfall (600–1400 mm yr⁻¹) environments. The Rotorua farm study used large paired-plots within paddocks (8 replicates), with Spikey®-GA treatment on one of each pair after all grazings. Pasture yield assessments using a rising-plate-meter indicated a 7-14% higher average pasture mass to Spikey®-GA at this site. There was no effect of Spikey®-GA treatment on N leaching (measured using 320 ceramic cup samplers) in all years. The Stratford study had separate Control and Spikey®-GA farmlets. It showed no significant effect of Spikey®-GA on pasture production but had significantly lower (<i>P</i> < 0.05) nitrate-N concentrations in leachate during late-winter/spring in the first two years and the same trend in the third year. Over three years, nitrate-N leaching averaged 38.1 and 30.9 kg N ha⁻¹ yr⁻¹ (<i>P</i> < 0.05) in the Control and Spikey®-GA treatments, respectively.</p>