Soil pH is a measurement of Hydrogen in the soil determined by using a 1:1 solution of water and soil.
Most crops in the corn belt like soil pH levels between 6.0 to 7.0. Soil pH between 6.0 and 7.0 insures
that essential nutrients are plant available if in correct concentration. Most soils east of the Mississippi
River are slightly acidic running 5.0 to 6.3 naturally. The Farm Clinic uses Sikora Buffer (a less
hazardous mimic of SMP buffer) to determine lime requirement with a target soil pH of 6.5. Buffer pH
is determined with a 1:1:1 water:soil:buffer solution and lime requirements are calculated based on the
Cation Exchange Capacity (CEC):
Cation exchange capacity is a measure of the ability of a soil to hold and release nutrients. The higher
the CEC the more fertilizer that a soil can hold and also the more fertilizer it takes to raise soil test
levels. We use CEC to determine the sufficiency ranges for Potassium, Calcium and Magnesium. The
Farm Clinic uses the summation of calcium, magnesium, potassium and hydrogen to determine CEC.
Soil Test Ranges:
The Farm Clinic uses five groups that are based on the chance of added fertilizer increasing yields on
most crops. The groups are as follows;
Very Low – 90 % chance of an increase of yield with additional fertilizer
Low – 75 % chance of an increase of yield with additional fertilizer
Medium – 50 % chance of an increase of yield with additional fertilizer
High – slight chance of yield increase with fertilizer but maintaining soil test here can be
Very High – no benefit to additional fertilizer
P,K,Ca and Mg
All of these nutrient test are processed using the Mehlich 3 extraction method and are read on an ICP.
Below are notes on nutrients that are tested giving their functions in the plant and also some in-site on
where, when and why recommendations are given on these nutrients.
Phosphorus: Phosphorus is an energy source for the plant and helps with root development, cell
formation, crop maturity and seed formation.
Potassium : Potassium in the plant increases protein production, improves water efficiency and helps
with standability in crops. Sometimes lower CEC soils have trouble holding on to this nutrient and
yearly applications are more economical.
Calcium: Calcium is essential in strong cell walls. If Calcium is low more than likely soil pH levels are
low and liming is needed.
Magnesium: Magnesium is the central atom in the chlorophyll molecule. If Magnesium is low soil pH
levels are usually low and can be fixed with a lime application unless the lime material is very low in magnesium (<4%).
This article was written by Farm Clinic for questions and service information contact Andrew Bailey by phone: (765) 659-1783