caverdude
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soil testing

I have been having my soil test done by the county extension office. I have heard of another independent lab called Logan labs. But that's not my question. In soil we have nutrients in basically two forms. Soluble and Insoluble right? So we have cations and anions that are readily available. If these are stuck in humus they don't show up on test or at least all of them don't. Therefore if you have a lot of humus and organic matter and biology in the soil then the soil is more fertile than a test would reveal. The other thing is that test do or don't show minerals that could become available with further breakdown of the soil? And I don't fully understand CEC Cation Exchange Capacity. Soil with high CEC with same results otherwise in nutrients is different than soil with low CEC right?

So it would be cool if we could just do a star trek scan or cat scan or something and get a list of minerals % in the soil of each Macro and Micro nutrient and percentage of each immediately available to plants. But this is not exactly possible right? Or is it possible but way too expensive to be worthwhile? or what?

imafan26
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Re: soil testing

Why make it so complicated? Yes, there are soluble and insoluble forms of many elements. Organic matter and organisms tie up a lot of those nutrients. Most tests tell you the total in the sample not what is available.

You can have a phosphorus in a very high range, even if you don't add anymore, it may still take years for the phosphorus to come down because much of it is in a bound form.

Nitrogen is rarely measured on tests because it is so volatile. The nitrate form is readily available, the nitrite must be converted by soil bacteria before it becomes available. Some of the nitrogen is converted by other bacteria that release the nitrogen back to the air, the soil organisms feed on the nitrogen and it is held in their bodies until they die and decompose, and not all nitrogen especially from organic sources are totally available or able to be extracted even over time. And some of it will leach with water. That is why even when all the other elements in a soil test is high there is still some minimum nitrogen recommendation.

If the total phosphorus , ca, potassium, magnesium, etc are high, don't add anymore. If they are low then add the recommended amount.

PH and the presence of other elements will to a large extent determine what elements are readily available and which will be bound or suppressed by other elements. The type of soil, presence of organic matter, moisture, and even time of year which will affect the activity of the soil microbes, has effects on the nutrient availability. The types of crops you select and whether you are rotating crops to keep nutrients more balanced and even the type of fertilizer you add manures, blood, bone meal, azomite, or synthetic matter in how they affect other elements in the soil, and the microbes.

In other words it will make you crazy if you think about it too much. There are a lot of variables and all you really want to do is stay somewhere in the middle of the road. It does not have to be exact.

First of all, look at the plants you are growing. If they are not showing chlorosis, stunting, or other nutrient deficiency, they are getting enough. If your soil test says you are high on an element, don't add more. It is a waste of money, will leach and would probably not be good for the environment, and if it gets high enough may interfere with the uptake of other elements. If your soil has a high cec, high in organic matter or clay, the soil will store many elements for years. Organic matter in soils tends to buffer pH so it behaves more neutrally, but it still is a good idea to keep your pH from going too much toward any extreme. Realize too, that no matter what you do, soil will always drift back towards its own equilibrium. You cannot fight soil that is basically alkaline, if you want to grow an acid loving plant, put it in a pot and just control the composition of the soil in the pot, or grow plants that can tolerate more alkaline conditions. Just don't keep adding anything that may make it worse.


Be aware the problem with organic sources of fertilizer is that they are rarely as pure as synthetics. You may be adding bone meal for the phosphorus, but you are also getting calcium since it is inherent in the product. If your pH is on the high side, more calcium is probably something you may not want. Manures are added for nitrogen, but the fact is they do not have a lot of nitrogen readily available and may take a couple of years for the manures to release most of what it has available. In the meantime if your phosphorus is high, manure which is relatively high in phosphorus is not as good a choice as blood meal which has more nitrogen and a lot less phosphorus.

Organic fertilizers need to be converted by the soil bacteria into a form that is available to plants. That is what makes them slow release. Most of their nutrients are tied up. Soil bacteria are less active in colder temperatures and release more nutrients in warm weather. For people who live in snow country, it does not impact them very much since they won't be growing much out in the snow, but people who use organic fertilizers where there is a longer growing season may see plants grow very slowly.

https://www.avocadosource.com/tools/fert ... les/ph.htm
https://www.agronomy.k-state.edu/documen ... uptake.pdf
https://www.lovesgardens.com/Attachments ... oklet1.pdf
Happy gardening in Hawaii. Gardens are where people grow.

caverdude
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Re: soil testing

Thanks for the links, looks like good reading material there.

Ha I'm just trying to understand on a deeper level I guess. I have read a book "Start with the Soil" twice so far. Feed the soil not the plants seems like an organic theme.

imafan26
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Re: soil testing

If you want a good book on the soil get Teeming with Microbes by Jeff Lowenfels. It is all about the soil web. I disagree with some of its premises but it is an excellent book for organic gardeners.
Happy gardening in Hawaii. Gardens are where people grow.

caverdude
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Re: soil testing

added it to the wish list, thanks

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jal_ut
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Re: soil testing

Interesting subject. Soil, yes it is where the plants get what they need. I must confess though even after many years of growing, I have never done a soil test. The local farmers here all add some nitrogen fertilizer each crop, so that is what I do too. That and always adding organic matter to the garden each season. Leaves, lawn clippings, manure..........
To keep the soil up, I think we should put more on it than we take off.
Gardening at 5000 feet elevation, zone 4/5 Northern Utah, Frost free from May 25 to September 8 +/-

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rainbowgardener
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Re: soil testing

"To keep the soil up, I think we should put more on it than we take off."


I love it! I think that about sums it up and is probably all we really need to know!
Twitter account I manage for local Sierra Club: https://twitter.com/CherokeeGroupSC Facebook page I manage for them: https://www.facebook.com/groups/65310596576/ Come and find me and lots of great information, inspiration

imafan26
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Re: soil testing

I don't think more is necessarily better. Just enough to keep things balanced. Adding more nitrogen and phosphorus has been the cause of algae blooms that are killing fish in steams and oceans and runoff that contaminates water and fields with salmonella and e. coli.

Pollutions of waterways and the ocean is one of the main reasons phosphorus was removed from laundry detergents and why no phosphorus fertilizers exist.

It also why there are regulations requiring dairies and piggeries to have a management plan for the manures.
Happy gardening in Hawaii. Gardens are where people grow.

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