# Need advice on Fall application of Potassium



## hatefoxtails! (Jul 20, 2010)

Our soil sample indicates that we need to apply 100lbs per acre potassium on our fields. We hay part of our fields and graze stockers part of the year.

The potash is fairly expensive. The people at the grange tell me that fertilizer is cheapest in the Spring and rises in cost through the Summer and into the Fall. The difference in price is a couple hundred dollars. 
My question- is Fall fertization with Potassium that much better for grass pastures then spring application? We have been battling foxtails and I have been told that a fall application of potassium wil help the grass out compete the foxtails.

Thanks!!


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## rjmoses (Apr 4, 2010)

First, is it 100 lbs of potassium or 100 lbs of potash? Potash is 46% potassium, so to get 100 lbs of potassium, you need to apply about 220 lbs of potash. For hay ground, this would be light; for pasture, it sounds about right.

Second, potash was running $615/ton last month here and I've been told that it will probably go up next year. I hedged my bet and bought 1/2 this year, waiting on next year. (There are only two companies in North America (US and Canada) that produce potash, but that's a different rant....)

Third, top-dressed potash only migrates about 1/8th to 1/4 inch into the soil each year so it will take time to work it way into the root system. Fall application allows the freeze/thaw cycle to suck it down faster.

Finally, putting potash on without checking your PH is ineffective. First, get the PH up to where it needs to be, probably in the 6.5-6.8 range, by liming. Again, top-dressed lime only migrates 1/8th-1/4 inch per year.

Hope this helps.

Ralph


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## hay wilson in TX (Jan 28, 2009)

Potash is easy.
There are three basic forms of potassium, & I assume the Lab is recomending potassium. 
One is Murate of Potash 0-0-60 and is usually limited to no more than 500 lbs/A. The reason for the limitation is it is really potassium chloride is an essential element that helps with disease resistance. Thing is too much is just that too much. One advantage is it is a salt just like table salt and is water soluble.

Then there is potassium sulfate 0-0-50, with this you can put all you want but you will want to limit the amount of sulfur in many soils.

Then there is K-Mag or 0-0-22K-11Mg-22S.

I like to apply 500 lbs/A Murate of Potash (300 lbs K) & 200 to 1,500 lbs K Mag for the magneesium and sulfur in the fall or prior to planting alfalfa. 
In addition I use much the same blend but only 200 lbs/A going into our summer drought expecting Luxurious Uptake with associated higher percentages of plant K which translates to better water economy.

If I used managed grazing and not hay production I could reduce the amounts by two thirds.

I look at plant analysis rather than soil testing for fertility management. HERE with this soil 320 ppm K is very deficient and 450 ppm K is sufficient. I really want the whole plant to test at 2.20% K, At 320 ppm the whole top will test at 1.00% K (NOT GOOD)

This is on calcareous, high shrink, 50 CEC high shrink clay soils in Central Texas not far I-35 & half way between Dallas and San Antonio.

Added Most soils are sufficient for K at 140 ppm K. The combination of high CEC and high shrink clay is why this soil needs to test so high just to have adaquate yields.


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## hatefoxtails! (Jul 20, 2010)

Thanks, yes this does help. Our pH is great. 6.6. 
We need 100 lbs of potassium according to our soil analysis. The fertilizer plant did the calculations for me..they were talking Murate of Potash. The fertilizer plant quoted me $717.40/ton, but they said the price of fertilizer usually goes down in the Spring.
We didn't get a chance to fertilize this Spring because it was so wet here in So. Oregon that we could never get it on before the grass got too long and the cattle were already on it. So I plan to put on 30lbs per acre of nitrogen also this fall along with the potash. I know have to be careful with nitrogen in the fall, but since we skipped it in the Spring, I think we should at least have a little to boost fall growth and get some reserves for the grasses. Does this make sense to you, or should I wait for Nitrogen application in the Spring?
I think, like you, I will hedge my bet and put 1/2 of the potassium on this Fall, and 1/2 on in the Spring.
Thanks again! Toni


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## hatefoxtails! (Jul 20, 2010)

Thanks, I am more familiar with soil analysis than plant analysis, but I may try that next year. How does the cost of plant analysis compare to soil analysis? Maybe it will help with our hay sales. I have heard that you don't want too much K in your forage.


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## hay wilson in TX (Jan 28, 2009)

hatefoxtails! I must admit fox tail grasses are not my favorites.

Hay analysis, For years I used a NIR feed analysis They charged $15. Then they went up to $20. I was ready to change because the only minerals reported were P, K, Mg, & Ca, plus nitrogen with the use of a little arithmetic. I switched to Midwest Labs with their wet analysis. Their reported nutrients were not as extensive as the NIR systems, but they reported a lot more minerals. 
I use the mineral analysis to monitor the soil fertility. 
Then Midwest went to $30 on a hay analysis. My customers are only interested in Crude Protein Therefor I changed to requesting their plant analysis rather than the hay analysis at $22 / sample. 
To find Crude protein I simple I simply multiply their Nitrogen percentage by 6.25. That is the old fashion method! A big advantage is I get all the essential elements we are usually interested in.

Too much potassium can be a problem, for cows the last month before they have their calf. This can result in Milk fever. After they have their calf their needs for potassium goes up again. 
Optimum levels of potassium varies with location. California with their near 100% irrigated alfalfa production they feel 1.70 to 1.90 % K is just fine. If you supply an abundance of water you do not need the water use efficiency we see with 2.65% K. 
With out irrigation I feel I really need 2.68% K but seldom have alfalfa or bermudagrass above 2.20% K. HERE alfalfa that test in the 1.70% K range does not persist.

Timing of potash application. 
Timing depends on your soil type. If you have a sandy soil it is recommended to fertilize spring AND fall. If you are close to having beach sand then spring, mid summer and fall might be better yet. If you are blessed with a clay loam soil you can fertilize any time you are in the mood. If you have a heavy clay soil and normally a summer drought, a heavy application of potash prior to planting and a light application prior to the summer drought.

Twice I have had a field Tissue Test reported above 3.00% K and a week later the hay analysis was below 2.50% K. Remember a true tissue sample is the top 6 inches of the alfalfa plant, while a hay sample is a sampling of the whole plant that goes into the hay bale.


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## hay wilson in TX (Jan 28, 2009)

I probably should mention a tissue sample is really a clipping of the growing plant, while a hay sample is a probe of the hay bale.

Both are subject to selection bias. All sampling is subject to random variability in the material sampled. 
With a clipping we may select the better looking stem, while another may select the obviously deficient stems. 
Sampling hay the person can sample to find the highest percentage of leaves for a better appearing report.

*On soil sampling *I have double and triple sampled the soil at each stop collecting two and one time three probes of soil each going into a separate bag. The results could have been for different reported locations. 
A professional soil consultant tells us he has two different sized probes, and at times he uses first the smaller & then the larger diameter probe and receives differing reported levels.

The lab it's self will have less than a 10% spread in results, but our soil samples for P, K, Mg, & Ca can have a 30% Scatter. 
If the truth is what we want, then we will not look for reliable soil analysis for Sulfur through copper.* The variability of these elements in the soil is simply too great for accurately reporting what the crop can find. *


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## hatefoxtails! (Jul 20, 2010)

I really do hate foxtails! They have persisted in our pastures due to bad advice from Extention agents, and ignorance on our part. That is why I am glad I found this site! We have had to deeply discount a large part of our hay because of them. We can never get them hayed in time before they head out. (we don't have our own hay equipment) Ok...sorry I got started on the subject









So, I could send hay bale core samples in and request a plant analysis which can be cheaper than a hay analysis. Sounds like it may be better and cheaper than a soil sample analysis. I will look into that. Thanks for the great information! Toni


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## hay wilson in TX (Jan 28, 2009)

Depends on what you cnsider cheaper.

A soil test is in the $10 range, while a tissue analysis is better than $20. 
I pull a hay ( pay for a tissue analysis) from each field and each cutting. If the same field is round baled and square baled sample each bale type and pay for two test.

If I the alfalfa looks nitrogen deficient I may spring for a Mo test which more than doubles the cost of the analysis.

The thing about testing is "Don't ask unless you can stand the answer."


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## hatefoxtails! (Jul 20, 2010)

I did my soil sample with AgriCheck here in Oregon and it was approx. $50. Maybe I am asking for more than I need. Ok, glad you clarified it...I pay for a tissue analysis from each field and each cutting. Thanks!


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## hay wilson in TX (Jan 28, 2009)

You must consider the customers needs. The Dairy wants feed values with a little mineral information. 
The grower wants enough to establi$h hay value and to learn enough from the mineral analysis to be able to evaluate soil fertility and avaialbility.

A reasonably good feed value is roughly $30 and a reasonably good mineral analysis is roughly $25. 
After price value I am interested in the N, P, K, Mg, Ca, S, Na, Cl, Fe, Ma, B, Cu, Zn, Mo, and possibly Co. If I ask for all those minerals my cost is $51. 
Normally I do not ask for Mo, Co, or Cl and that is $22. Here price is set by protein and protein is Nitrogen percentage times 6.25.


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