AgResearch scientists have developed a smartwatch-like sensor which listens to a cow urinate, measuring the amount of nitrogen hitting the pasture.
Livestock farming comes with several environmental challenges but one of the main ones is the contamination of waterways from nitrogen which comes from the urine of dairy cows.
Scientists at AgResearch wanted to measure the nitrogen impact on pasture and to see if it differs from cow to cow.
They developed acoustic urine sensors which are strapped to the back leg of a dairy cow - they record the sound every time the cow urinates.
AgResearch senior scientist Brendon Welten said typical dairy cows urinated 10-12 times a day, with an average volume of two litres each time.
"That's an average equivalent urinary nitrogen application rate estimated to be approximately 600kg of nitrogen per hectare," Welten said.
"But research has shown that there are some cows that urinate more frequently but in smaller volumes, so their nitrogen load is spread out more."
When this happened, plants utilised more of the nitrogen rather than it going down through the soil and eventually ending up in the waterways, Welten said.
"This is a great farm management tool - once farmers have this farm-specific urinary nitrogen loss information of their dairy herd, this could be used in a decision support tool like Overseer to allow potential immediate benefits in reducing farm nitrogen loss relative to using a default model value.
"Furthermore, farmers can then use it to make farm management decisions, such as breeding and culling, to move their dairy herd towards lower nitrogen loss potential and thereby provides the opportunity to achieve sustained reductions (year on year) in farm nitrogen leaching loss."
Welten said AgResearch was in contact with the dairy industry to roll the sensors out on farms around the country.