Spikey tests N Leaching

By Jackie Harrigan.

COW URINE HAS THE POTENTIAL TO DEPOSIT nitrogen to the tune of 1000kg/hectare, with the average pee event depositing the equivalent of 600kg N/ha, and has long been understood to be a major contributor to nitrogen leaching through New Zealand soils.

Research has focused on developing and testing mitigation options to decrease N leaching,

One is the use of Spikey technology which identifies animal urine patches after grazing and uses targeted application of a Nitrostop product to treat the urine patches. Nitrostop is a giberellic acid, commonly used onfarm to enhance growth and N uptake and has the potential to reduce pasture percentage of N, and reduce the excreta-N ratio in urine:dung.

A farmlet grazing trial at the Dairy Trust Taranaki Stratford dairy farm with paired 25ha farrnlets involving standard practice (Control) compared to use of Spikey on paddocks after each grazing.

The Stratford demonstration farm runs 3.6 Jersey cows/ ha on free-draining volcanic soil with an annual rainfall of 2,050 mm per year. The study commenced in spring 2020 is ongoing, and Ryan Barlow, AgResearch Ruakura gave an update on the results to the Farmed Landscapes Research Centre conference at Massey University in early February.

Nitrogen leaching is measured using 150 ceramic cup samplers in each farmlet spread across 12 paired paddocks. Nitrate and ammonium N concentrations are measured regularly and linked with drainage data from lysimeters and water balance calculations to determine N leaching.

Two years of measurements of N leaching have shown a strong temporal pattern with highest nitrate concentrations in winter. During late-winter and spring of both years, the nitrate concentrations in leachate and amounts of N leached were significantly lower in the Spikey farmlet.

In year one, the average nitrate leached was 54.0kg N/ ha and 45.0kg N/ha for the control and Spikey treatments respectively. Corresponding estimates for year two were 38.2 and 35.0kgN/ha. However, the annual N leaching was not significantly lower.

Other lysimeter studies by PRL have shown reduced N leaching from urine with NitroStopTM across NZ. The trial also found grazed farmlet studies have high spatial variability from urine patches and ceramic cup (or other) methods need treatment differences > ~20%+ to achieve statistical significance.