A soil test is no better than the care given to taking samples. Follow the guidelines in Table (below) for taking soil samples. Not following these instruction or the instructions from your soil testing lab can invalidate your soil test results and interpretations. It is very important to completely and accurately fill out the soil test information sheet that goes to the lab with the sample (Figure: "Sample soil test results"). Mailing kits for submitting samples to the Agricultural Analytical Services Laboratory are available from all Penn State Cooperative Extension offices.
Table: Guidelines for taking soil samples
- Do not wait until the last minute. The best time to sample is in the summer of fall.
- Take cores from at least 15 to 20 spots randomly over the field to obtain a representative sample. One sample should not represent more than 10 to 20 acres.
- Sample between rows. Avoid old fence rows, dead furrows, and other spots that are not representative of the whole field.
- Take separate samples from problem areas if they can be treated separately.
- In cultivated fields, sample to plow depth.
- Take two samples from no-till fields: one to a 6 inch depth for lime and fertilizer recommendations, and one to a 2-inch depth to monitor surface acidity.
- Sample permanent pastures to a 3- to 4-inch depth.
- Collect the samples in a clean container.
- Mix the core samplings, allow to air-dry, and remove roots and stones.
- Fill the soil test mailing container.
- Complete the information sheet, giving all of the information requested. Be sure to include the soil name. Remember, the recommendations can be only as good as the information supplied.
Sampling No-till Fields
If the area has been in no-till corn management or long-term perennial grass for two years or more, it is advisable to use a reliable field kit to measure the pH of the surface soil. Surface applications of nitrogen fertilizers and manure may acidify this layer rapidly and decrease herbicide and nutrient effectiveness. Collect several cores less than 2 inches deep from the no-till area and mix thoroughly in a clean bucket. Remove a sample for pH measurement. Simple colorimetric pH kits normally are the most satisfactory for field use. If the pH of the surface soil is less than 6.2, take a standard soil sample for laboratory analysis. Apply the recommended lime as early as possible before corn plantings.
If this standard sample does not indicate a need for limestone and the surface pH is below 6.2, apply 2,000 lb/A of calcium carbonate equivalent. This amount should be adequate to neutralize the acidity created by the surface-applied nitrogen fertilizer.
Reference: The Agronomy Guide - Section 2: Soil Fertility Management
Table: 1.2-2 from The Agronomy Guide