Agriculture Reference
In-Depth Information
Location: Center Point, Kerr County, Texas
Element
Mehlich 3
AA 8.2 pH
Ideal Soil
C
ation
E
xchange
C
apacity
71.35
11.15
pH of Soil Sample
7.60
7.60
Organic Matter %
4.06%
Sulfur
S- ppm
20
K x 0.50 =
109
Boron
B ppm
1.02
2.0
%CEC
%CEC
%CEC
Base Cations
ppm
ppm
ppm
Calcium
Ca++
96.81%
13815
86.64%
1932
83.50%
1862
Magnesium
Mg++
1.34%
115
3.89%
52
10.00%
134
Potassium
K+
1.73%
482
8.78%
382
5.00%
217
Sodium
Na+
0.12%
19
0.74%
19
1.50%
38
Unlike the Walnut Grove soil, the Center Point soil has a very high level of Ca and
a good reserve of K but is seriously lacking in Mg. The aim should be to increase
the level of Mg and displace some of the excess Ca from the exchange sites. If
the M3 test estimated CEC of 71.35 had been used to make the calculations,
Ideal Mg at 10% of CEC would have been 856 ppm rather than the 134ppm Mg
"ideal" listed above.
The Rx written for the Center Point garden and orchard called for 2180# of
Magnesium sulfate MgSO
4
7H
2
O (Epsom salt).At 10%Mg and 14%S, that would
add 218# of Mg and 305# of S, or 109ppm Mg and 153ppm S, a little more than
the amount needed to raise Mg to 134ppm. The next pair of soil tests after the
present growing season will tell if that was enough Mg to reach the desired
target.
Magnesium sulfate is a more costly and less concentrated source of Mg and S
than Magnesium Oxide and agricultural Sulfur, but was used in this case because
Magnesium oxide is not allowed under USDANOP rules.
10# of Solubor 20% B was also recommended, adding 2# or 1ppm B to the topsoil.
This is a high Calcium soil and we wish to have optimum levels of B available.
There would be little danger of adding too much Boron to this soil with the
extremely high level of Calcium it contains.
Calcareous Soils with pH < 7.0
As mentioned above, some sands have developed partially from eroded
limestone.Asoil largely composed of these calcareous sands, in a humid climate
or when heavily irrigated as on lawns and golf courses, may have a measured pH
below 7 but contain significant amounts of undissolved Calcium or Magnesium
carbonates. These can be extracted by a Mehlich 3 or other acidic soil test and
give a false high estimate of CEC. If one suspects they are dealing with a soil like
