Thursday, 2 April 2015

Coated urea not the only tool in the N-loss toolbox


There’s been a bit of noise in the market recently around coated urea that can reduce volatilisation - the process where nitrogen is lost to the atmosphere rather than available to the plant.

The trouble with all this averaging and aggregating up is that farmers may think they need a coated urea when their farm conditions would actually make it unnecessary.

Basically, there is more than one way to skin the N-loss cat.

With the current state of dairy payouts, everyone wants the same thing. It’s all about the amount of N you get to keep for your plants relative to your conditions in your part of the country.

Under all but the most extreme conditions such as being hot, dry and windy and applying high rates of N, the losses in pastoral farming situations are expected to average 10 - 15% (or less) of the N applied as urea. Any claim of coated products reducing N-loss by an amount like 50% can be a bit misleading because that does not mean half of the total applied nitrogen. Rather, the claims mean half of the 10 - 15% which of course equals 5 - 7.5%.

How much N does this mean is being saved for plant growth? Well, if you apply 65 kg urea/ha (30 kg N/ha) and lose 10% to volatilisation, you are losing 3 kg N/ha and with the coated urea you will reduce this to 1.5 kg N/ha (at 50% reduction of volatilisation).

At times, the premium for a coated product can be 8 to 10% more than standard urea.

As a famous psychologist once said: “When the only tool you have is a hammer, every problem looks like a nail.” If a fertiliser company with a coated urea tells you it’s the only solution to volatilisation, they should also inform you of the several other ways that volatilisation can be tackled.

There are at least FIVE other simple steps you could consider to help reduce volatilisation:

1. Apply lower rates each application e.g. 30-50kg N/ha (volatilisation rates increase with higher rates of N application).
2. Apply when it’s raining or about to rain or use at least 10mm of irrigation straight after application.
3. Apply to pastures with some leaf cover.
4. Avoid hot, dry and windy conditions.
5. If applying to soil, incorporate so it is just below the surface.