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Soil Testing

There are different ways of testing your soil. An experienced gardener can examine a handful and generally determine if it is a high clay or high sand soil by its look and feel. One can also get a rough idea about the amount of organic material from inspection.

 

However, it you wish to actually measure the amounts of clay, silt and sand, there is a home test which you may perform. The instructions are outlined here:

 

Soil Classification Calculator

 

This test supplies you with information about soil texture, but will not give you information about soil fertility. To do this you need to collect soil samples from each of your unique garden areas, bring it to OSU Extension office where it will be sent to OSU Stillwater for a test. The cost is $10 per sample and the turn-around time is about 2 weeks. It is important that the soil samples to be tested are collected properly, The instructions for collecting the samples and information about interpretation are listed here:

 

Soil Test Instructions

 

Soil Test explanation

 

Leaflet 240: Soil testing...The Right First Step

 

This soil test will inform you of your soils pH (acidity) along with the amounts of nitrogen, phosphorus and potassium. The report will also include recommendations about correcting the pH, if needed, and which and how much fertilizer to use to correct nutrient deficiencies.

 

Soil test results of over 1000 samples submitted by Tulsa area homeowners in 2007 show some interesting findings. The results are summarized below.

 

Average Results of Soil Tests for Tulsa County Homeowners 2007

 

 Measurement

Average Value

Optimum Value

Mobility in Soil

Comment

pH (acidity)

6.6

6-7

NA

Generally no adjustment needed for this acidity level

Nitrogen

22

40

Very mobile

Most soils will need extra nitrogen added

Phosphorus

162

65

Very immobile, attaches to soil where it is placed

No addition of phosphorus, elevated concentrations may take years to return to normal

Potassium

299

250

Moderately immobile

Most soils have enough potassium, more is not needed.

 

The take home message from these test results is that a landscape previously regularly fertilized usually has too much phosphorus and potassium. To add more is harmful to plants and can pollute our environment. Excessive phosphorus is particularly harmful when it gets into the waterways. This is such a problem that some Midwestern states have a law banning the use of phosphorus on lawns unless there is a soil test documenting its need.

 

HLA-6436: Healthy Garden Soils, Earth-Kind-Gardening

 

HLA-6007: Improving Garden Soil Fertility