The Importance of Soil Testing

Don’t guess, soil test!

Soil testing is a critical part of producing a successful crop, whether that be fruits, vegetables, forages, turf, or ornamentals. A soil test informs us of the fertility of our soil by telling us the levels of several essential nutrients present, as well as the relative acidity or pH. These results aid us in selecting plants, preparing our soil, selecting and applying the correct fertilizers, and identifying problems. Overfertilization can cause excessive plant growth, increase diseases, lead to increased pollution, as well as just being costly. Soil testing gives you precise measurements, leading to better decision making and ultimately more productive plants.

When you are considering growing a crop, the first thing you should do is conduct a soil test. This can help you make appropriate decisions and prepare your land accordingly.

Soil testing is the only reliable way to test soil pH. Soil pH affects nutrient availability to the plant. Most nutrients are at their optimal availability to plants between a soil pH of 6 and 7. However, some plants such as blueberries require more acidic soils. A soil test will tell you the pH, as well as provide you with recommendations to modify the pH for your selected crop. Substances such as sulfur can lower soil pH, while substances such as lime will raise soil pH.

Soil testing can be done at any time, however, you will want to give yourself time to allow for adjusting pH before planting if that is necessary. Depending on the substance used, It can take 6 months or more for added lime to begin providing benefits. 

So you know why to test your soil, but how do you do it? Soil testing is a service provided by Virginia Tech. You want to sample your soil when it is not too wet. Sampling in the fall is usually best for farmers to allow for adjusting pH. You want to divide the area into units if the area or field is not uniform, or if different areas are unique (garden, lawn, flower bed, crop field, etc.) You want to obtain a good, representative sample of soil. Sample in a zig-zag pattern across the area. Samples should contain at least 5 subsamples from the area mixed together, with each subsample taken at a depth of around 6 inches for plowed land, or 4 inches for pasture or lawns. You may sample with tools such as a soil probe or spade.

Soil probe with a soil core sample

The soil information sheet must accompany any sample sent to the Soil Testing Lab. This sheet can be found online or at your local VCE office. Take time to fill in the blanks to the best of your knowledge. If you need assistance your Extension agent can help you. Make sure the sample identifier on the sheet matches that of the sample box, and that you fill out the correct plant code for the sample you submit.

Soil tests at Virginia Tech are $10.00 per sample for a routine package. Routine tests make recommendations for the following: P (phosphorus); K (potassium); Ca (Calcium); Mg (Magnesium) and five micronutrients, as well as pH. Commercial farmer samples are free of charge. Results are typically received within a week, unless there is a delay due to a large number of samples being sent in.