Monday, March 25, 2013

Soil Testing - How To

Judging from the response in the stores about custom programs, this week’s article about how to take a soil test might be of some help. I like to compare a soil test for a gardener to a blood test for a doctor. When I have a physical, my doctor has me take a blood test about two weeks in advance. She (I have a lady doctor) has time to look at the results and make recommendations based on the results by the time I get there for my appointment.

If the blood lab mailed me the results directly or I picked the results up from the lab, I’m sure I would not be able to tell if my good cholesterol was high enough and my bad cholesterol was low enough. What is the ratio of these two numbers? Are my thyroid, liver, and gizzard working properly? Am I getting enough vitamin A, B, C and D? Are they in the right ratio? What is my blood sugar? I end up paying the blood lab over 500.00 for the lab fees, and the doctor her fee for her interpretation of the results, which usually goes something like this - eat like a vegetarian only in very small portions and exercise like an Olympic athlete.

The custom program is similar to the doctor’s visit. When most people look at soil test results from the lab, they comment on the soil pH. They never comment on the buffer pH, which is more important in determining lime recommendations. In all my years of working with soil tests, I have never heard a customer comment about calcium to magnesium ratios, or it looks like I need 5 pounds of ProMag 36 per thousand square feet to get the 1.8 pounds of magnesium I’m lacking.

Turf grass areas
Proper interpretation of soil test results depends upon collecting a representative sample of the soil. Soil samples can be taken at any time of the year.  Samples are most easily collected using a PVC pipe, garden trowel or spade.
¨       Each soil sample should be a composite of subsamples collected from randomly selected spots within the chosen area.
¨       Soil Sample should be 3 inches deep straight down.  These samples should be equal parts of the first 3 inches of soil.  Avoid pie shaped samples that have more of the 1st inch of soil and less of the 2nd and 3rd inches.
¨       Take 5-10 subsamples for relatively small areas (less than 1000 square feet) in home lawns.
¨       Collect the subsamples in a clean plastic pail, mix the soil thoroughly, and put about one cup of this mixture in a sample bag.
¨       Remove grass, thatch and debris from sample.
¨       One sample per lawn should be good unless you have different types of soil or grass.

Landscape Beds
¨       Soil Sample should be 6 inches deep.
¨       Repeat the steps above.
¨       Please remember to record the location of your samples
(Rose bed, flower bed, shrub bed etc…)

Test results include
¨       pH, Buffer pH (when needed), Available Phosphorus, Exchangeable Potassium, Calcium Magnesium, Cation Exchange Capacity (CEC) and Percent Base Saturation
With recommendations for:
            Nitrogen, Phosphate, Potash, Magnesium and Lime - based on plant type and use
¨       Sodium can be tested for an additional charge. Very important in Lowcountry. We see a lot of high sodium yards in areas that you would not expect sodium to be an issue. Many wells around here also have high sodium (salt) in the water they put out.
¨      Other tests are available including tissue samples; however, these are our most common two.