Facts and Figures about Nitrogen and Dairy Farming

Some facts and figures

To appreciate the enormously of the problem, We need to look at some figures.  Dairying in NZ makes up 25% of New Zealand’s export earnings. There is approximately 1.8 million hectares of dairying land.  In NZ there are 5 million dairy cows. The average number of cows per hectare is approximately 2.85.  74% of dairy herds are in the North Island and 34% of that are located in the Waikato.

On average the rate of nitrogen applied by fertiliser is 100kg/ha/year.  In 2007 there was 45kg/ha/year of nitrogen leached.

I have learnt that cows can consume a great amount of pasture a day (90-110kg) and drink anywhere from 15-60L of water.  Then they getting rid of anywhere from 30-60kg of faeces and peeing anywhere from(15-30kg). Nitrogen is in various forms in the urine.  Ammonia (volatile gas) Ammonium  and nitrates.  The cows are consuming all the nitrogen that is available in the paddock (???) to them and realistically a cow only requires about 200g of N per day.Therefore there is rather a large of amount of excess,

Urine only covers about 2% of a paddock after grazing.  Only a quarter of a paddock will get N from urine over a year.  Hence one of the reasons that Nitrogen must be applied by fertiliser.

In Autumn and Winter when there are large amounts of rain this where nitrogen leaching can cause a problem.  One method that is used to reduce amount of urine and faeces going on a paddock is to stand cows off grass, this is where Cows are put on a pad for various amounts of time over a 24h period.  Eg.  Cows are on grass during day and on pad at night.

From this research and background reading I am beginning to get an appreciation for the imbalance of N in our system there is.  Hopefully this trial can shed some light on some other possibilities that could help reduce nitrogen leaching.   

Some information courtesy of DairyNZ Research Technician - Chris Roach