Quantity of organic fertilizer question

11 years ago

I am new to organic gardening, so this may be an obvious question, but something has confused me lately.

I am trying to grow fruit trees organically. The information sheets from my local extension agency recommend large amounts of fertilizer (non-organic of course). Usually several pounds a year for a larger tree, depending on the variety. They usually recommend something like 8-8-8.

So why is it that recommended amounts for organic fertilizers are so much smaller? For instance, I purchased some Aggrand Natural liquid fert that is only 4-3-3 and it just recommends a few ounces per gallon of water that is then spread over 100 sq. feet. (so I use one gallon on several trees)

And they only recommend that application several times a year. There is no way that gives anywhere near the quantity of fert that the extension agency recommends.

So where does the difference lie? Do trees not need as much fert as they say? Or are organic ferts only supposed to be supplemental to other methods? If that's the case, it would seem the majority of nutrients would be coming from other places, so why even bother with the organic fert?

(just as an example, the recommended amount of fert for my 2-yr-old avocado is 3-6 lbs per year. But if I use the recommended amount of Aggrand, it would only come to a couple ounces of liquid fert per year, if even that. Why are the quantities so different?)

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Comments (3)

User
11 years ago
Apply compost and mulch, as much as possible.

Organic growing is much more than replacing fertilizers and such with versions that have the 'organic' stamp on them, although there are plenty of organic fertilizers that work well.

About the fertilizer recommendations, there may be a range for the 'best' amount of fertilizer to apply rather than a single value. For example, suppose you gave (in addition to natural soil and rainfall conditions) the avocado tree:
1 pound of fertilizer and got 10 more pounds of avocados);
2 pounds of fertilizer and 20 more pounds of avocados (compared to no fertilizer);
3 pounds of fertilizer and 25 more pounds of avocados (compared to no fertilizer);
4 pounds of fertilizer and 28 more pounds of avocados (compared to no fertilizer);
5 pounds of fertilizer and 30 more pounds of avocados (compared to no fertilizer).

At some point too much fertilizer will 'burn' the tree, let's say 7 pounds of fertilizer.

As you can see there is a diminishing return - the first pound of fertilizer applied gives a 10 pound increase in yield and the fifth pound of fertilizer gives an additional 2 pounds of avocados. I just made these numbers up for demonstration, this is not from any actual data although I'm sure these tests have been done many times in many fields.

If priority is given to yield per tree or yield per area with less concern for fertilizer cost then the recommendation might be to use 6 or 7 pounds of fertilizer. If priority is given to getting the most yield out of each pound of fertilizer applied with less concern for number of trees or space then the recommendation might be to use 1 or 2 pounds of fertilizer. In the real world, a combination of factors might be considered to come up with a cost effective fertilizer application recommendation.

There's more to consider. The plants will do better and the fertilizer will work better if the soil is improved (see compost and mulch), and applying the fertilizer certain ways will work better (smaller amounts more frequently, watered into the soil) than others (scattering a large amount all at once). If you continue to follow this approach of: get a soil test, find out what is low, find that in a bag or package and spread it on the field, repeat - you are in a way using the land until it 'runs out.' If you think a little differently however and make use of compost, mulch, cover crops, rock dusts, you will be building and improving the soil, going in the 'other direction' if you will.

Orchard Mulching and Cover Crop Trials

Page 22 shows that they recorded the lowest yield using glyphosate and that any mulch type resulted in a larger yield. Alfalfa appeared to be one of the best for the trees but it didn't necessarily suppress weeds that well compared to the others. Wood chips were recommended.
Kimmsr
11 years ago
You should be able to get information about growing fruit trees organically from those people at your extension office, ask. Unlike the synthetic fertilizers, organic fertilizers nutrients are not very soluble so they are not readily available, easily tested.
What you need to do is get the level of organic matter, the humus or residual OM level, to around 6 to 8 percent in your soil. Get the pH of that soil into the range those fruit trees need. Work on getting the Soil Food Web active, and not be too concerned about how much NPK you pump into the soil. Get the nutrients in your soil in balance which should mean not throwing something 8-8-8 at the soil in the hope that will be what the plants need.
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wardog25
Original Author
11 years ago
Thanks for the advice. That helps.

In addition to the Aggrand, I have mulched the trees with a combination of grass clippings and pine bark.

Planning to do some composting as well, but that is still in process.

Quantity of organic fertilizer question

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Kimmsr

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wardog25
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Quantity of organic fertilizer question

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Kimmsr

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wardog25
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