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Little River, TX | Unadjusted CEC 30 ish, adjusted CEC 15-20.
John you have my interest on this one. I never heard of adjusting a CEC. I am intrigued.
As I understand Cation Exchange Capacity is a function of clay and to some extent organic matter. The clay and organic matter have a negative charge while cations have a positive charge and are attracted to the clay & organic matter.
The Laboratory I work with does not like any CEC value to be above 30 meq/100g, though when I paid them to actually measure my CEC they consistently report 50 meq/100g. It is not cheap as they charge me $40 per sample. Their results for the measured CEC is very consistent while their preferred computed CEC fluctuates wildly & rotates around their idea of 30 be as high as a CEC should ever be.
To compute the 30 CEC they report my calcium levels down in the 3500 ppm range. Historically my 8 pH soil will have 7,000 ppm Ca, to 9,000 ppm Ca. I never really look at calcium, here, as I know it is excessive.
A stylized version of the computed CEC equation is:
K/w + Mg/x + Ca/y + Na/z = CEC in meq/100g
When I substitute the known CEC value and use Ca as the unknown, the computed Calcium will range from 7,000 ppm to 9,000 ppm Ca.
With the clay soil we have here in the Texas Blacklands we need to have a soil test at least 400 ppm potassium, to a high level at 600 ppm K.
The Texas Blacklands run roughly from San Antonio, through Dallas - Fort Worth & on to the Oklahoma border, and is about 80 miles wide. From here to San Antonio the soil has a high pH and overlays calcium rock. From here north the pH can be neutral to slightly acid, in pockets.
I hope I was correct when I told a global warming neighbor that there is more CO2 tied up in the White Cliffs of Dover than in all the Tropical Rain Forest. | |
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Soil Tests and knowing your soils
