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Nutrient mobility in the soil

Nitrogen cycleJeff Lowenfels' book provided a handy way of dividing up plant nutrients --- by how mobile they are in the soil.  Understanding nutrients' mobility helps explain why certain soil nutrients can be present in the soil but unavailable for your plants, and why others might not stay put when you add them to your garden.

At one extreme lie the nutrients that are very mobile in the soil and tend to float into plants along with water.  As long as there's enough nitrogen in the form of nitrate, sodium, boron, and chlorine to go around, you won't see deficiencies in your plants.  On the other hand, these mobile nutrients tend to wash away in heavy rains, so those of you who live in rainy climates like I do will want to make sure you provide mobile nutrients only when plants are actively taking them up.

At the other end of the spectrum, phosphorus, copper iron, manganese, and zinc (and, in tropical soils, sulfate, nitrate, and chlorine) react chemically to soil particles.  Plants have a very tough time taking in these nutrients without the help of mycorrhizal fungi, so you can often see a deficiency in your plants even if (for example) there's plenty of phosphorus in Peak phosphorusthe soil.  This is one reason why farmers worry about the world running out of phosphate fertilizers --- they're pouring phosphorus into the soil far faster than plants can use it rather than keeping the soil healthy so fungi can bring plants the phosphorus that's already there.

In between these two extremes lie most of the positively-charged nutrients, which are attracted to soil particles a bit like a magnet to iron.  Roots have to trade a positively-charged hydrogen ion for each cation they take in (a process known as cation exchange).  These semi-immobile nutrients include nitrogen in the form of ammonium, potassium, calcium, magnesium, molybdenum, and nickel.  If your soil is low on these cations, it's probably because you haven't built up your organic matter enough to hold them in place so your plants can trade for them.

Stay tuned for tomorrow's post to learn more about how plant nutrients make their way into roots.

If your pantry is overrun with homegrown root crops, check out my ebook to learn how to turn a junked fridge into a root cellar.



This post is part of our Teaming with Nutrients lunchtime series.  Read all of the entries:





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I noticed that you are reading Jeff's books on soil health. He's a big no-till advocate and local garden expert up here in Anchorage. He's an attorney by trade, but he writes a regular garden column for the Anchorage Daily News for years and he lets us know when its time to do anything garden since timing is everything with our short growing season.

I know his books can seem pretty dense, but they always seem to produce some really profound insights that make wading through the details worth the effort. Glad some local talent is getting some Appalachian coverage!

Comment by David Tue Sep 24 12:55:52 2013
I just like that your writing method , correlation(soil irons with mega-nut and iron ) and examples..
Comment by Balamurali Thu Nov 3 08:34:42 2016

One very unique homestead, $1,500 per acre, the opportunity of a lifetime