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on another soil test. Those who believe

they always do are all too often making

some very serious mistakes.

For example, farmers and growers who

request soil tests from our company are

advised that calcium should occupy 60-

70 percent of the soil’s cation exchange

capacity. There are other labs who use

the same guidelines, but still others

who advise 65-75 percent for calcium

(Ca) saturation on their soil analysis.

The target we shoot for on medium to

heavy soils is ideally 68 percent. But

that same soil sent to three other labs

will not measure 68 percent. One will

report it as 64 percent. Another reports

it as 74 percent. And still another

shows 80 percent. Yet all four labs are

considered as within the tolerance

range for measuring and reporting

calcium levels on that soil.

The lesson here is to learn and follow

directions from the laboratory you

are using based on their numbers,

not a test from some other lab whose

numbers could vary considerably

and thus lead to wrong conclusions.

Sometimes only Ca, Mg (magnesium)

and K (potassium) are given as 100

percent of the total soil nutrient

saturation from a soil testing lab,

while on tests received from some

other labs, sodium and other bases

also contribute to that 100 percent

total. Consequently, a farmer could

have a field day and tell everyone he

had to reach 80 percent calcium in his

fields before attaining his top yields.

If the intent is then to take a soil to

80 percent as that farmer found to

be beneficial, be sure to send it to the

same lab for analysis before deciding

to spend what it takes to achieve

that percentage. If a soil test from a

different lab shows 68 percent calcium

saturation when the lab that farmer

uses shows it as 80 percent, then it

can be a costly mistake to buy and

apply the calcium required to reach 80

percent on the test that is showing 68

percent.

Potassium

Potassium is another example of how

number differences on test reports can

be misleading. To be most effective

for growing crops on the test we use,

potassium should be a minimum

of 2 percent and a maximum of 7.5

percent to avoid problems caused

by having too little or too much. For

example, from the test we use, farmers

are advised not to drive potassium

above 7.5 percent because that will tie

up boron availability and above this

level also increases weed pressure in

the field. Farmers and growers can see

this happening to their crops and in

their fields. Yet when the same soil

is tested by another very reputable

soil laboratory, they report that soil

as having 8.5 percent potassium.

For those who think 7.5 percent on

one test means the same on tests

from other labs, this now becomes a

bone of contention, bringing claims

that soil test numbers are just not

reliable. If farmers using the test

that recognizes the same results at

8.5 percent as the other test at 7.5

percent, then the numbers on the

tests are certainly reliable, it is just the

ability of the user to interpret those

results that must be learned.

But such differences as described

in the paragraph above can cause

complications when striving to

educate farmers and growers about

the value of using soil tests. Another

problem with high potassium

is that when combined with the

sodium percentage, and both added

together total 10 percent or higher,

this will cause manganese uptake

to be blocked from the plant, even

on soils that show to have excellent

manganese levels. But this is not true

on the soils that show potassium as

8.5 percent, because then the soils

have to be at least 11.00 percent

before that happens, and that is

assuming that sodium would be

Continued on Page 22

Soils that test high in magnesium still grow crops that are deficient in magnesium.

Photo courtesy of Neal Kinsey, Kinsey Ag Service.

20

Organic Farmer April/May 2019

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