# Leaching of nutrients thru soil



## jdhayboy (Aug 20, 2010)

I have some questions about nutrients leaching thru the soil in relation to CEC value given in a soil sample, Maybe someone has some insight to. 
I just went thru my samples and the vast majority of my CEC values are from 2-4. 
Question is... How much and how fast do nutrients move thru soil with a specific CEC in relation to amount of rainfall received? 
Higher CEC means nutrients are able to stay suspended longer in root zone for plant uptake. Colbys frost post reminded of these questions I have, so I wanted to ask. For example, with a soil CEC value of 3, if I were to apply 200 units of potash on march 1st and we averaged 2 inches of rain each month til august. Let's say we get 4 cuts first, may 15. Second. June 20, third July 25 and fourth august 30. And before each cut 70 units of N was applied. At what point, have all the units of K passed thru your optimal soil zone? Are u getting more units up front in your yield and less as you cut more? Was the plant able to utilize all 200 or did they move thru the soil to fast to be taken in? So if potash is $.50 per unit and plant used 100 units per acre and the other 100 units leached on thru, we lost $50 an acre in theory. 
Just trying to be efficient with my inputs. I did a few fields like this last year, which made me ask these questions. This year I had thought of maybe applying 100 early and another 100 in late June or early July or something. Thanks in advance.


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## mlappin (Jun 25, 2009)

Wow, CEC's of 2-4?That's some really light soils, our most drought prone is around 5 or so, the gumbo on the home farm is in the upper 20's.

I try to do split applications no matter the crop. I spread potash right after first cutting hay, then more potash with boron towards the end of August on all the hay ground. Corn gets some N with the turndown, some more again with the 10-34-0 while planting then again with straight 28% while spraying right after planting. Then we side dress 28% as well. On our heavier soils we could probably apply all our N right before planting, but on the lighter soils the split applications really help.

You don't specify what the forage crop is. Alfalfa has some mighty deep roots.


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## Mike120 (May 4, 2009)

In the South Texas sand, my father insisted on many light light fertilizer applications instead of a couple of heavier ones for that reason. Diesel was a lot cheaper in those days as was fertilizer.


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## vhaby (Dec 30, 2009)

To have this low CEC your soil must be something like a Katy fine sandy loam. See

https://soilseries.sc.egov.usda.gov/OSD_Docs/K/KATY.html

Was the soil CEC estimated from analysis of calcium, magnesium, potassium, and sodium values on a soil test, or was an analysis done to specifically determine CEC? CEC values estimated on analysis of these four nutrients can be higher than the soil's actual measured CEC because the extracting solution used to determine these four nutrients is acidic and will dissolve unreacted limestone applied to correct soil acidity or native calcium carbonate in alkaline soils. This leads to misleadingly high values for plant available soil calcium levels and therefore misleadingly high CEC levels.

To attempt to provide a reasonable answer to your question, soil clay has a net negative charge. Therefore, positive charged plant nutrients such as calcium, magnesium, potassium, and sodium (referred to as cations) do not simply hang around as suspended nutrients in soil solution but they are attached to the negatively charged soil clay, somewhat like the positive charge of one bar magnet to the negative charge on another bar magnet. Plant roots can take up these cations from the clay by providing hydrogen ions to the clay to exchange, for example, calcium ions off the clay and into the soil solution from where they enter the plant root.

Potassium has a single positive charge, so it is held less tightly to the clay than is calcium. Many soil scientists will tell you that potassium doesn't leach (move through the soil with water) but that is not exactly true. When you apply limestone to an acid soil, or fertilize with potassium or other cations, the added cations, when dissolved in soil water can exchange the original potassium (as an example) from the clay and the applied cation will then adsorb (become attached to) onto the clay. The original potassium cation then moves downward to attach to another clay particle. In this manner, potassium can move through the soil via a series of exchanges. This movement is nowhere near as fast as the negative charged plant nutrients (called anions) like nitrate, sulfate, and chloride that are repelled by the negative charge on the clay. Anions can move downward (leaching) or upward somewhat freely with the movement of water.

Since potassium moves through the soil relatively slowly, plant uptake is responsible for most of the loss of residual and applied potassium from your soils. If you are producing hybrid bermudagrass for hay and selling it, you should be applying about as much potassium as you are nitrogen. The ratio of nitrogen, phosphate (P2O5), and potash (K2O) should be similar to a 5-1-5 in your applied fertilizer, unless your soils already have a very high soil test level of potassium. This does not mean that you need to apply potassium or phosphorus every time nitrogen is applied. For example, if your soil's phosphorus level is very low or even low by soil test, all the phosphorus for the year should be applied with the first nitrogen application. If the soil's phosphorus level is in the medium or low end of the high category, then small amounts of phosphorus can be applied each time nitrogen is applied without incurring a phosphorus deficiency in the bermudagrass.

Relative to application of potassium to a low potassium testing soil, at least half of the needed (recommended) potash should be applied with the first nitrogen application. The remaining recommended amount of potash may be applied after the second cutting, assuming that 3 - 4 cuttings are made during the season.

One other point- fertilizer is applied as pounds of plant nutrient, not units as are mistakenly used when actually meaning pounds. In my early soil science studies, a unit of feritlizer was something like 20 pounds. A unit of fertilizer is no longer a commonly recited or written term in the fertilizer industry.


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## jdhayboy (Aug 20, 2010)

thanks for the responses. We are growing hybrid Bermuda grass. And I was hoping mr haby would chime in. I gotcha on the lbs of material, 200 units of k is approximately 334 lbs of material per acre in a 0-0-60. What I am beginning to see is the more in depth chemistry side to soil that you are defining. And no I don't believe my samples were taken to test CEC values. Here's what a sample said " CEC 2 ; %h 0 ; %k 5 ; %ca 74 ; %mg 20 ; %na 2. I have a binder full of info regarding each of my fields soil texture. I had all my fields mapped, like row croppers do, to pull samples to see if there were any soil nutrient deficiencies amongst soil variations. I don't know if anyone has ever done this in bermuda grass or not be it that the mapping may not pay for itself. But for it was a big education as to what's going on in my soil and it answered a lot of my questions but created some more as well. Just thought of this... If they ran the variance machine in the field to find soil variations, that would more accurately define my CEC values correct? All fields have 3 different soil zones and all samples were pulled within specific zone.

Back to your chemistry... Is sandier ground more positively charged? Compared to negative charge clay? Just so I understand better are you referring to the charge given to an electron ? Little negative symbol above the e? So that's why cations move more quickly thru sandier soil right? Because they aren't able to grip or bind on much as they pass thru.

Something you might find interesting mr. Haby. We own property in what I would call Katy prairie land. Rice fields and open flat ground. That land is just across across the street from where all the hay fields are. Hay is much more rolling and deeper sand. According to some research information I have on our property location. This specific area was the natural levee for the brazos river tens of thousands years ago. Which to me might explain going east is a reduction in elevation as is west towards the brazos which is 30 miles away. Like I said, go south just across the fm road and you the only hill you might find is an ant mound until you hit a sand dune on the beach. Go north maybe 5-10 miles at most you start into iron ore kinda ground. I thought that was pretty interesting.


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## jdhayboy (Aug 20, 2010)

https://soilseries.sc.egov.usda.gov/OSD_Docs/H/HOCKLEY.html

Accidentally stumbled on this. In section, type location, it says soil type ends 100 ft south of fm road 2920. That's what I was referring too, pretty neat to visually see the change and experience the difference between them.


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## vhaby (Dec 30, 2009)

"thanks for the responses. We are growing hybrid Bermuda grass. And I was hoping mr haby would chime in. ??? I gotcha on the lbs of material???, *200 units of k* is approximately 334 lbs of material per acre in a 0-0-60."

Guess you still don't have it...not 200 units of K but *200 pounds *of k...

Actually, 200 *pounds* of K[sub]2[/sub]O equals 333 *pounds* of material as 0-0-60.

"Back to your chemistry... Is sandier ground more positively charged? Compared to negative charge clay?"

No, not really. Sandier soil still has a net negative charge because of the clay it contains. Sand-sized soil particles have little if any charge. The negative charge is in the clay. Positive charged plant nutrients (cations) might move faster through a sandy soil compared to a heavy clay soil because there is much less clay to provide negative charges to adsorb and hold the cations in the sandy soil compared to the clay soil. And yes, the negative charge is like electrons.

The fertilizer industry labels potassium (K[sup]+[/sup]) as K[sub]2[/sub]O in its bags and blends, whereas testing labs test for and report the amount of K[sup]+[/sup] their analytical procedure extracts from the soil. When I suggest that the amount of potash (K[sub]2[/sub]O) applied for hybrid bermudagrass hay production should equal the amount of nitrogen applied on an annual basis to a low K testing sandy loam type of soil, or a 5-1-5 ratio of N - P[sub]2[/sub]O[sub]5[/sub] - K[sub]2[/sub]O such as a total of 300 - 60 - 300, the amount of actual K applied equals only 249 pounds. There is only 83% K in K[sub]2[/sub]O. Plants take up K[sup]+[/sup] not K[sub]2[/sub]O. Confusing, isn't it? Actually, the potash referred to as K[sub]2[/sub]O is mined and then purified as potassium chloride (KCl), and the Cl is a plant nutrient. Now it gets really confusing.

So, why doesn't the fertilizer industry label their bags and blends with the amount of K in the bag rather than K[sub]2[/sub]O? Guess they want us to think we are getting more for our money than we actually are getting in plant nutrient value.

I'm somewhat familiar with the soils you refer to. A long time ago, I did some limestone research on, at that time, the Charlie Fry farm near Waller, TX. If I'm remembering correctly, we turned west or southwest approximately across from Prairie View A&M.


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## jdhayboy (Aug 20, 2010)

Now I GOTCHA, Thanks for defining the proper terminology. It just sounded right to me say a 100 lbs of material has 60 units of k. And maybe you already answered this... But what is the rest of the 40 lbs? The 2O in k2O? And then on top of that out of 60 lbs only 49.8 are actually used by the plant in the form of K+ . 
So out of 100 lbs of material we have only 60% which we consider to be usable, but in all actuality only 83% of the 60 can be taken up by the plant as a nutrient K+ . For a total of 49.8% . 
Is most of the dead weight created during the refining process? And necessary to actually give us K+ in a form that we can apply easily? 
Sorry for all the questions? Figured I would ask since i know the answer I can take to the bank.


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## vhaby (Dec 30, 2009)

jdhayboy said:


> ...what is the rest of the 40 lbs? The 2O in k2O?


Potash, the historic term used to represent the K[sub]2[/sub]O, is mined underground. The mined product contains potassium chloride (KCl) and sodium chloride (NaCl). The KCl is separated from the NaCl. Purified KCl contains 52.4% potassium (K). The 52.4% K in KCl converts to almost 63% K[sub]2[/sub]O. Since the KCl separated from the mined product is not pure (it contains some sulfate and possibly some sodium), the KCl sold as ferilizer converts to 60% K[sub]2[/sub]O, thus the 0 - 0 - 60 used in the fertilizer blends.

The remaining 40% is chloride (Cl) and the few impurities. Remember, Cl also is a plant nutrient, but you don't read or hear much about it because few scientists do research on the benefits of Cl for plant growth and when fertilizing with potash, an ample supply of Cl also is provided. Research in Oregon, South Dakota, Montana, and Texas, to name a few states, has shown yield increases from application of Cl for crop production. Some of these yield increases attributed to Cl application were the result of plant disease reduction.


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