# Diamonium Phosphate Application vs. Availability



## Texasmark (Dec 20, 2011)

Hi,

Got my soil test back and N was less than half what I need for the crop I mentioned, and phosphorus was roughly 2/3. K was coming out my ears, and sulphur requirement was slight at 5# per acre. Ph was 7.6 in alkaline soil (Houston Black Clay).

Somewhere in the back of my mind I recall that what P you distribute this year won't be available till next year.

I plan to apply my fert. using a tractor mounted conical spreader (pretty common) and as soon as I get it out come back with my tandem disc dragging a spike harrow to smooth it out. Then in several days, or maybe looking for a day before rain, drill in my Pearl Millet and tow a roller/packer behind the drill.

So, I am wondering if this year's crop is going to be stunted, or will I be able to pick up some of the P I put out this spring.

Thanks,
Mark


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

*K was coming out my ears, and sulphur requirement was slight at 5# per acre. Ph was 7.6 in alkaline soil (Houston Black Clay*).
Not all black land dirt are the same. Some have a high pH but not an excessive amount of calcium. In fact some actually are neutral or even slightly acid. 
There are a good half dozen different clay types represented. 
I have only studied the calcareous clay that is a high shrink type.

Here with my 4 to 10% free lime phosphate starts returning to a form of rock phosphate within days of application. There are several things we can do to slow the process. 
Surround the phosphate with Ammonium, concentrate the phosphate by placing the fertilizer in bands or both. Supposedly the product Avail will also buffer the phosphate from reacting with the free calcium.

In years past TAMU reported phosphate in abundance while the farmers found they had a positive response to phosphate fertilizers.

Phosphate is easy. Potassium is a little more difficult. With the high shrink swell clay's they clay is constructed by a series of interconnected plates of silicon. With this clay potassium not only is attracted to the clay surfaces by an electrostatic charge, common to all clay soils, but also a good supply is trapped in the openings between the plates. When the clay is moist the plates swell and trap the potassium. 
The soils labs dry the soil samples, which opens up these spaces and their chemistry finds and reports trapped potassium as available.

Then there is the Cation Exchange Capacity effect. The surfaces of a clay has a negative charge while K, Mg, Ca, Na, and other cations have a positive charge. The higher the CEC you soil has the higher our soil has to test to have adequate availability for each of the cations.

Lucky me with a calcareous, 8 pH, 50 CEC, Vertisol clay soil. What this says is that I NEED a soil test in the 400 to 500 ppm K range ( not a 140 ppm K) to have adequate availability of potassium.

None of this was learned 60 years ago, at SWYSTC at San Marcos, and is seldom acknowledged by soils labs. 
Some of this information I gleaned from Penn State, some I learned from questioning Midwest Labs, and a good bit was learned from vhaby on these pages. A Matt Hagny contributed as has a John Haggard, both of whom frequent the http://talk.newagtalk.com pages.


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