Ag Notes: Many benefits of soil testing

October 20, 2004|JERRY LITTLE

If you want to increase crop yields or vegetable and flower garden production next spring, have your soil tested. This is the only way to determine whether the soil has the right alkalinity or acidity to release available nutrients.

The measure of soil acidity is pH. It controls availability of all other nutrients. Generally, Agronomic crops grow best when the pH is between six and seven. Some horticultural crops such as azaleas and blueberries require much more acidic soil conditions, in the range of 4.5.

An incorrect soil pH can cause problems. For example, a low soil pH can induce a calcium deficiency; while a high one can cause iron and zinc deficiencies.

Soil test results will give you research-based information on how much lime to use to make the soil more alkaline or sulfur to apply to make it more acidic.


Having the proper levels of soil nutrients will help maximize economic yields. This is increasingly important this year, because increasing energy costs mean high fertilizer prices. In fact, farmers can expect to pay about 30 percent more for potash (potassium fertilizer) this year compared to last year.

A good soil testing program will maximize returns on your fertilizer investment by identifying fields that already have sufficient nutrients and those with inadequate fertility. Higher fertilizer prices make blanket applications increasingly expensive.

The past two growing seasons have been ideal for crop production, resulting in record yields in many areas. Additional soil nutrients have been removed with harvested crops. These fields likely are lower in essential nutrients and therefore will produce highest return on your fertilizer investment.

Soil testing also enables landowners to identify environmentally sensitive areas. For example, excessive phosphorus can cause low oxygen levels in lakes and streams that may lead to fish kills.

Many Kentucky soils are high in phosphorus

Many Kentucky soils, especially in the bluegrass region, are naturally very high in phosphorus. A soil test will reveal these levels so no additional phosphorus fertilizer will be added.

Fall is a good time to take samples for soil testing. Each county Extension office has information on taking soil samples and sample bags. There is a nominal fee to cover the soil analysis costs.

Taking soil samples in the fall gives you plenty of time to carry out the recommendations. For instance, agricultural lime takes about six months to decompose and react with the soil; so it needs to be applied in the fall. Fertilizer prices usually are cheaper in the fall and soil is drier so it is easier to get into the field.

The turn-around time for soil tests usually is faster in the fall.

You need to take different samples for various land uses such as agricultural fields, lawns, garden, fruit trees, ornamental shrubs and azaleas because these may have distinct fertility and acidity or alkalinity requirements.

Take a sample from poor growing area and from adjacent areas of good growth. Mark each sample with a letter, or numbers on a field map. Collect at least 10 soil cores for small areas and up to 20 cores for larger fields.

How deeply you take cores for farm use depends on the tillage system used. For tilled areas, take cores from the surface to plow depth, usually six to eight inches. Take cores down to a four-inch depth in no-till fields and pastures.

Go about four inches down for lawns

For home lawns, take cores from the surface down to four inches. For gardens, ornamentals and fruit trees, take cores down to six to eight inches.

Be sure to take all cores from an area at the same depth.

After you've collected soil cores, put them in a clean, dry plastic bucket, crush the soil and thoroughly mix it. Allow this to air dry in an open, contamination-free space. When it dries, fill the sample bag and completely fill out the information sheet.

A separate sheet is needed for agricultural soil, home gardens, lawns and turf grasses and commercial horticultural crops.

It's a good idea to take core samples around the same time ach year to compare results from year to year.

To obtain the most accurate soil fertility report, contact county Extension office for more tips on properly taking samples.

Jerry Little is county extension agent for Agriculture/Natural Resources

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