Novel methods for estimating urinary N production from two contrasting dairy systems

Mark Shepherd1, Diana Selbie1, Gina Lucci1, Paul Shorten1, Maryann Pirie1, Brendon Welten1, Kevin Macdonald2, Chris Roach2 & Chris Glassey2

1 AgResearch Ltd., Ruakura Research Centre, Private Bag 3123, Hamilton 3240, New Zealand, [email protected]

2 DairyNZ Ltd., Private Bag 3221, Hamilton 3240, New Zealand

Abstract

Two demonstration farmlets representing the grazed pasture component of contrasting dairy systems were established in 2011 in the Waikato region of New Zealand to compare production, profitability and mineral nitrogen (N) leaching risk.  The farmlets ran for four seasons and differed in: annual N fertiliser input (c. 150 vs. c. 50 kg N/ha), with stocking rate adjusted to available feed (3.2 vs. 2.6 cow/ha); and also in hours grazed during autumn and winter.    We report on three methods for estimating urinary N production from the systems, which is the primary source of N leaching from grazed paddocks.  We compared a herd N balance calculation and two novel methods: direct measurement of the urine patch N immediately after voiding onto the soil and urine sensors which, when attached to the cow, provide real-time measurements of urine production over a 24 hour period.  The three methods differed in temporal and spatial scale of measurement but produced consistent conclusions.  The low N system generated 19% less urine per ha as a mean of the three measurement methods but the same amount of urine N per cow. When cows in the low N system were removed onto a ‘stand-off’ pad for 6 hours per day, the urine sensors estimated a further 23% decrease in daily urine deposition directly on paddock.  Using a combination of methods provides insight into N flows through complex farm systems.