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Posts Tagged ‘controlled release’

I’ve already been accused of making things too complicated this week.  But it seems its worth reading labels and even safety data sheets when it comes to fertiliser.  It all started with two empty pails of Osmocote I had at home. Bought from Bunnings. Casually looking at the label of the All Purpose Landscape mix I noted 2.2% magnesium and 0.2% iron.  Then skipping over to the Native Gardens mix I saw 0.2% magnesium and 2% iron!  A typo maybe?  Maybe the two were mixed up?  The Safety Data Sheet for the native mix from Bunnings says less than 1% each of iron chelate, iron sulphate, magnesium sulphate and magnesium oxide.  That doesn’t really compute and its not that helpful. Oh well lets move on. Lets look at the commercial stuff.  Osmocote Pro low P 8-9 month has 1.8% Mg and 0.2% iron. The normal landscape 8-9 month has 1.2 and 0.33 as iron chelate.  Seems reasonable.

Now check the SDS of both commercial products.  Well the first line is interesting!  The commerical products are both based on ammonium nitrate as the N source.

Have a look at the Bunnings versions.  Instead of being 30-60% ammonium nitrate they are both 30-60% urea!  Less than 10% ammonium nitrate.  Now I don’t know about you but I don’t know any 8-9 month slow release urea formulations – usually more like 4 months.  So while both are called Osmocote there are fundamental differences between the commercial and the Bunnings formulations.

Does it matter?  Probably not that much on the nitrogen side of things.  The Bunnings versions of each say to reapply every 6 months so a bit shorter than the 8-9 month commercial ones.

The magnesium is a worry though.  Magnesium is sort of between a trace and  a macro element and leaf tissue concentrations generally run at around 10-20% that of N and K.  I can’t see 0.2% supplying a plants needs.  And as I noted previously the magnesium content in Nutricote is similarly abysmal.  Perhaps that’s why Epsom salts (magnesium sulphate) gets such a good rap!

And a final reminder about iron. If you’re using any potting mix with wood waste or pine bark in it, they adsorb iron.  We have always added something like 500-1000g/cubic metre of pinebark potting mix.  You might get away with as little as 200g for other wood based materials.  But make sure it is iron – combine chelate and sulphate if you wish but don’t try to do it with mixed trace elements – you will end up with boron toxicity.

 

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A few weeks ago I posted on the stupidity of controlled element formulations.  I can now add to that post as I have received some more information about a few other fertilisers.  The one that’s really been interesting is Troforte™.  I specifically looked at Troforte™ Native.  The really interesting thing is how much higher than all other products is the iron concentration.  The magnesium is not bad either, nearly three times higher than the Macracote™ Grey  range but not as high as Baileys Native or some of the other Polyon™ formulations.

I am will to bet that the superior performance of Troforte™ observed by many has more to do with the amount of iron in it than any added microbes!  A dangerous statement I know but until someone provides me with proper experimental evidence to the contrary I think I will stick by that comment.  Now iron is cheap as chips to buy so you could try adding more iron to any other controlled release product, especially if using it in a wood based mix – and maybe a bit of magnesium too depending on the analysis.  Or you can just dig a little deeper in your pocket and pay the extra for Troforte™.

The disparity in nutrient contents between fertilisers makes it very hard to make a fair comparison between products. Invariably even the N, P and K don’t match up let alone getting down to trace elements.  This is why I am always highly skeptical when someone says one product is better than another.  Seldom are you comparing apples with apples.

Troforte™ is also the only product on my spreadsheet to state a calcium content.  That doesn’t mean the rest don’t have any but its not stated, not even on the SDS sheet and I did ask for complete analyses.  A few other products also don’t state copper, molybdenum or boron contents although their SDS sheets do show those elements to be in there.  Now some plants do require boron in reasonable amounts – carnations, cauliflower, apples and strawberries, for example, so if there truly wasn’t any in there, that would prossibly cause a problem.  Many of these products are imported from America.  A part of me wonders if the lack of boron might be because some irrigation water over there is high in boron and the line between deficiency and toxicity is quite fine.

I don’t have the money to go and analyse all these products but it would be nice to know what really is their analysis.  And why do manufacturers have to be so cagey about what’s in their products.  Not all, but some.  I have encountered this before while working in the Department.  We were compiling a fertiliser spreadsheet that required inputting the analyses of all the fertilisers.  Some resellers were really helpful and quite upfront.  Others were not!

Plant nutrition is not rocket science. There are no secrets.  But I suppose that means there would be no marketing edge for any company wouldn’t it? 🙂

 

 

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So you’re standing in the aisle at Bunnings and you are being confronted with about 50 different fertilisers.
There are fertilisers for azaleas, citrus, veges, fruit trees…………
Then there are fertilisers you dispense through the garden hose, those you put a spoonful in a bucket of water, the controlled release, the powdered, the liquid, granular…………….
Oh and don’t forget the organic, the natural, the hydroponic………………….

Are you worn out yet? How do you make sense of all this?

First stop – the label. It should have something like a list of ingredients on it. It may go something like:
Nitrogen (as urea) 12%
Phosphorus (water soluble) 2%
Potassium (as sulphate) 8%

If it’s a liquid there should be something to indicate that those % are w/v (weight by volume), if its solid/dry/granular it will be w/w (weight for weight).

Next thing to look for is a rate – how do you dispense this product? One handful per square metre? One capful per bucket, one spoonful per 20 cm pot?

Lets look at the liquid feeds first – they are the most complicated. They will usually give you a measuring cap or a teaspoon and say use one of these in a 8L bucket of water (for example).

If they are really good they will tell you the volume (if it’s a liquid) or weight (if its powder) of the measuring cap or the teaspoon! If not you might have to weigh it yourself. To get an accurate result on your kitchen scales you might need to do say, 10 spoons and divide the answer by 10.

So lets suppose your powdered fertiliser comes with a spoon that hold 4 g product (when level) and you put that in 8L water. The analysis of your product is 22:4:15 (N:P:K) % w/w.

That means there is 22 g nitrogen in 100g of the powder. So one measuring spoon of the powder contains 22 x 4/100 g nitrogen = 0.88 g nitrogen or multiply by 1000 to get milligrams or mg: 880 mg N.

Put that spoon in 8L water and you get a solution that is 880/8 = 110 mg/L nitrogen.

You can repeat that for the P and K.

Take another liquid fertiliser and read the label. This time it says 10:3:6. And it says take the same sort of measuring spoon full of powder and put it in 5L water. The final solution will be 10 x 4/100 = 0.4 g N or 400 mg N/5L water = 80 mg/L N. So a bit weaker that the other one. Which is fine if its cheaper to buy but if its more expensive think again!

For liquids the sums are much the same except the analysis will be w/v so your 10 unit of N as in the last example will be 10g/100mL or 1g/L of product. If your measuring cap holds 20mL and you’re putting that into 5L water the sums are:
10 g/100mL means 10 x 20/100 = 2 g N or (2000 mg). In 5L water that’s 400 mg/L – quite a strong solution!

I recently went through this exercise from a supposed wonder product from the US – a liquid one at that and came out with something like 0.8 mg/L nitrogen as applied! It would have had to have been wonder product to do anything! Not only that liquids are often not very cost effective because you are shipping water around the countryside – very inefficient. Bear that in mind when you buy any ready-to-use product, typically those ones you attach to a garden hose and water on – they are terribly expensive for what you are getting in terms of chemical. They are convenient but you are paying for it big time!

It’s worth doing the sums. Kevin Handreck in his book Gardening Down Under did this exercise with about 20 products and the final nitrogen concentration went from 45 mg/L right up to 900mg/L! And I’m sure there wasn’t much correlation with price!

We’ll have a look at solid fertilisers next time.

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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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Fertilisers are a bit of a black box for most people.  Walk down any hardware or garden centre aisle and be confronted with an endless array of products all designed for different plants and situations.  But is it really that complicated?

Plants all need the same elements – nitrogen (N) and potassium (K) in the greatest amounts and often in about the same quantities give or take.  Phosphorus is only required in about 10-20% of the amount of N and K. Next come magnesium and calcium and then a whole array of others – sulphur and trace elements.  While plants might take up nutrients in differing amounts it often doesn’t matter what ratio they are in the soil, they will take up what they need.  Or in the case of nitrogen often more – that is called luxury consumption.  Unlike humans, plants don’t get fat though they just get overly leafy, sappy and prone to pests and diseases.

What about the type of fertiliser?  Are organics better than chemical fertilisers?  What about slow release or controlled release fertilisers?  And liquid versus granulated?

Liquid fertilisers – those that you buy as a powder or liquid and dilute with water are the ultimate in instantly available and quick acting.  Unfortunately in sandy soils the next time you irrigate, or if it rains, they will all be gone.  They are good for seedlings that have a small root ball because you can place it just where its needed and you can apply as little as you need.  So for a typical 6-8 pack type seedling you might only give each plant 50mL max but you might do that every 2, 3 or 4 days in the first 2-3 weeks.  No point in fertilising the whole bed, most will be totally wasted.  Just the plant.

Granulated fertilisers like NPK Blue are good when the plants get slightly bigger.  Sprinkle around the canopy area and do every 1-2 weeks for veges.

Sheep or other animal manures are also good but can be relatively high in phosphorus and contrary to popular belief, a lot of the N, P and K in them is water soluble and therefore instantly available and liable to be leached.  Animal manures may have to be aged to avoid burning from ammonia and they may carry weed seeds.

Slow release fertilisers are great for plants that don’t need to be pushed and are long lived.  So most garden plants, fruit trees if you wish, pot plants etc.  They are available in many formulations including low phosphorus for natives.  So anything from 3-4 month to 8-9 and there are even tablets that last 12 months.  The way these all work can vary.  Some are plastic coated and rely on the slow breakdown of that coating to work.  For others the fertilisers are embedded in a slowly soluble matrix.  Temperature ultimately controls the rate of release and for most the time frame on the label is worked out at about 21ºC.  In our hot summers it will be much quicker.  The disadvantage of these types of fertiliser is the rate of release may be too slow for some quick growing crops but otherwise they are excellent.

It is possible to get single element slow release fertilisers.  The most common available to the home gardener is nitrogen.

More on plant nutrition next time.

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