The Nitrogen Problem and What to Do About It
Cow Urine and Fertiliser Urea
In most cases, the largest source of loss of N from intensively grazed pastures in New Zealand are cow urine patches, particularly as nitrate leaching and nitrous oxide greenhouse gas emission. Application rates in the urine-affected ‘patch’ are typically 500-1000 kg N/ha, mainly as urea, vastly more than the most vigorous pasture can recover.
The second biggest source of loss is direct loss from fertiliser urea, principally as nitrate leaching and ammonia volatilization. The latter can occur at much cooler conditions than farmers are generally lead to believe, because many other factors, such as soil moisture, micro-soil pH and wind, are equally or more important.
There are direct and indirect methods to reduce urine-N losses. Indirect methods include (a) better balancing of energy and protein in daily feed intake to reduce excess N intake and voiding in urine, (b) the use of feed pads or cow-homes with run-off collection, especially in winter, and (c) time-limited grazing combined with stand-off pads with run-off collection, again for irrigation. Each of these have their own practical advantages and disadvantages.
Direct methods have included mechanically spreading the whole pasture with nitrification inhibitor, such as Ravensdown’s eco-N suspension or Ballance’s dcN granules. Both were expensive, and required 2-6 applications per year depending on the situation and climate. Use of a double inhibitor, containing urease inhibitor as well, has been shown to be more effective in university studies. Regardless, both products have now been removed from the market, due to Fonterra’s concerns regarding DCD residues in milk.
Alternative approaches include the ‘Taurine’ tail-attached device under development by Quin Environmentals (NZ) Ltd, with assistance from Bishop Research Ltd. This simple device is a tail-attached supply of ÒRUN®, a little of each each time the cow raises its tail to urinate.
Direct gaseous losses from granular urea fertiliser are most effectively and reliably achieved by coating with a urease inhibitor such as Agrotain. Other techniques such as coating with elemental S or humate are generally less reliable or too expensive. Typically, Agrotain coating can increase the extra DM produced for every kg of N applied per hectare by 20-40%, for example from 10 kg extra DM (EDM) per kg N applied to 14 EDM/kg N applied.
Fluidised Urea Incorporating Urease Inhibitor
However, a superior method to improve the efficiency of granular urea is to turn it into a thick fluid containing urease inhibitor. Either support trucks carrying grinding mills and mixing tanks, or pre-prepared agitator-fitted fluid/suspension tanks, are required.
For application on smaller areas of flatter land such as dairy farms, Quinspread Technologies Limited developed new spreading-truck technology, which converts granular urea into a thick fluid container urease inhibitor on-truck (Nhance), as the truck is spreading. Consequently, no additional staff or equipment are required. However, the equipment is very expensive, gives a narrow spreading swath and requires high levels of maintenance. The consequent high spreading costs have limited the uptake of this option.
And now ONEsystem®
To read all about this very exciting breakthrough, go to the the Global Sustainable Farming section of this website. For me, this is the most exciting fertiliser development program I have ever initiated.