Archive for August, 2012

Sorry this has been a long time coming.  I think we will have a look at nitrogen since it’s the most problematic nutrient in our sands.  Here today, gone tomorrow!

Nitrogen is mostly taken up by plants in the nitrate form so any other form of nitrogen has to be converted.  There is evidence that plants can directly take up organic nitrogen.

Common ways of applying nitrogen

1) In chicken manure (urea) or compost (ammonium and nitrate)

2) Ready made fertilisers eg NPK Blue, Nitrophoska, citrus/rose/whatever type of fertiliser (usually ammonium nitrate)

3) Controlled release fertilisers eg Osmocote (potassium nitrate, ammonium nitrate), Nutricote (potassium nitrate, ammonium nitrate).

4) IBDU/Ureaform (urea)

5) In liquid fertilisers such as Aquasol (urea) or Thrive (urea)

6) In fish emulsion (organic N, often supplemental urea)

You may hear comments about urea being harmful in winter.  This is because it requires conversion to ammonium (by an enzyme in the soil called urease) and then soil bacteria convert the ammonium to nitrate (nitrification) when it can be used by the plant.  In cold weather, soil bacteria slow down and the build-up of ammonium can cause damage to plants.  I have never seen this in Perth except when people toss on heaps of chicken manure.

Most of the nitrogen in poultry litter is readily available. Between 6%–30% is in the form of ammonia which will be lost to the atmosphere unless incorporated, the rest of the nitrogen will be lost within about 6 weeks unless taken up by the plant.  Even nitrogen applied in compost will easily leach.

The best organic sources of nitrogen are blood or chicken feathers – both about 12% N.

In Perth’s sands there isn’t much to hold onto anything.  If you add clay minerals they help retain more ammonium but nitrate tends to leach regardless.  The conversion of ammonium to nitrate occurs rapidly, especially in warm weather – within 24 hours.

Slow or controlled release fertiliser technology is great.  Products like IBDU or ureaform give slow release of nitrogen over about a three month period.  Other slow and controlled release products that contain phosphorus and potassium are all good but often can release too slowly for things like veges which have high growth rates.  This is where liquid feeding can be helpful but remember to only apply enough to saturate the root ball.  In the case of new seedlings that may only be a few mL per plant.  Anything you apply beyond that area is wasted.

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