Fast acting vs. slow release fertilizer

Hi,

I'm continuously trying to educate myself on soil culture and I have recently seen a few suprisingly negative properties of fast acting fertilizers. Apparently fast acting fertilizers can kill worms and change or reduce beneficial microbe populations which makes the soil less fertile. I have read that superphosphate will kill worms and I suspect high levels of nitrogen such as those found in lawn fertilizers will also.

I supect I'll get a few posts berating me for the use of any chemical fetilizers but I'm hoping someone that actually knows something about chemical fertilizers will chime in. Here are some questions/comments to get things going -

I believe nitrogen in all commonly available forms (Ammonium Nitrate, Ammonium sulfate, anhydrous ammonia etc) are all fast acting. To make these forms of nitrogen act in a slow release manner with infrequent applications requires a binding agent like that in Osmocote. Is it fairly accurate to say that applications of the above forms of nitrogen at the typically recommended rates may never the less be detrimental to microbes etc.?

Even boxed fertilizers labelled "organic" contain super phophates (phosphorus) and potash (potassium). Occasionally I see other forms of P, K but these are by far the most common. Are these inherently slow acting? I have read that one or more of these are not water soluble. Do small amounts of super phophate kill worms or microrganisms or it is just the large infrequent applications that do harm?

One of the most interesting articles I saw was on the use of lawn fertilizers. These are extremely fast acting especially with regard to N to promote fast greening. The downside is the negative effects on worms and microbes. I have stopped using these and I now use Osmocote (a 1 yr formula with micro nutrients included) on my lawn.

I'm not going to stop using fertilizers but I would like to use them in a manner that simultaneously promotes long term soil health and maximizes flower production on ornamentals if this is possible. My strategy thus far is to use Osmocote at low rates (sometime even lower than the published low rates for for plants that perform better in low N situations). During bloom periods, I supplement with a 0-10-10 or 4-10-10 or similar.

Plants can only use inorganic forms of nitrogen. You may want to read this (http://extension.missouri.edu/explore/envqual/wq0253.htm) article from the University of Missouri. It will give you a pretty good overview of forms of Nitrogen and how they differ. When you say "fast acting", I assume that you mean water soluble fertilizers such as Miracle Gro.
Controlled release fertilizers such as Osmocote are largely dependent upon soil temperature to determine the release of their nutrient into the soil. If you look at most slow release fertilizers, you'll see that their release rates are guaranteed only within a narrow range of soil temperatures, usually around 70 degrees. If your soil temperatures rise to 100 degrees, which is common in most places, especially in containers and baskets, this type of product will release its nutrient up to 40 times faster. Therefore, in many cases your slow release reaIly isn't. If you buy a bag of potting soil containing slow release fertilizers, if it has sat outdoors for any period of time, the slow release fertilizer will have broken down long before you get it home. One watering and it's gone.
In the case of slow release or water soluble, your problem is one of buildup of nutrient salts into the soil. When this happens, you run the risk of root burn unless you periodically "leach" the salts with clear water. Of course, all that does is move the salts through the soil and out of the root zone, and will ultimately enter the water table. Water soluble and slow release fertilizers are not particularly efficient except under greenhouse conditions, and far too much goes to waste.
There's a new product called FertiSorb which puts the nutrient into a super absorbent polymer, so it works with water rather than soil temperature. The polymer holds the nutrient until the root grows through the polymer and pulls it out. Once you water and allow the granule to absorb the water, the nutrient becomes available and remains in the root zone. FertiSorb isn't appropriate for lawn use, because the product needs to be in the root zone, but it's good for baskets, containers and flower and vegetable beds.
I hope this has been helpful.

been helpful to me

Hey alexh,

I know you said you were not interested in going organic, but when you started talking about earthworms and the health of the soil microbes as well as slowing the release of nitrogen, I could not resist responding. The best way to get more worms and improve your soil and have a slow release of nitrogen is an organic program.

Instead of retyping all this stuff I have some good links.


Synthetic vs organic:
http://www.dirtdoctor.com/view_question.php?id=131

Info on nitrogen and synthetics:
http://www.dirtdoctor.com/view_question.php?id=1404

General info:
http://www.dirtdoctor.com/view_question.php?id=1005

David

organic fertilizers usually are also considered slow acting. as far as nitrogen bloodmeal
is organic for nitriogen. organic fertilizers usually are higher in n-p-k than listed because they can only include the readily available nutrients. I believe the main concern with synthetics is the over-use of.
sometimes you might need a fast acting fertilizer which are usually single nutrients and they are called chelated. such as iron.
I think nitrogen is the quickest nutrient to be depleted in the soil.
There's a good book by Mary Pratt "Practical Science for Gardeners"includes an invaluable perspective on fertilizers and why she sometimes uses a little of both, organic and chemical.