Generally, soil tests for P, K, pH, EC, calcium (Ca), magnesium (Mg) and micronutrients will not change immensely from year to year; these can be analyzed every two to three years. Conversely, levels of NO3-N, SO4-S and Chloride (Cl-) can change from year-to-year and should be analyzed every year a non-legume crop is planted.
Soil samples should represent a uniform area of your field; take time to assess fields and split them up by differences, such as texture, color, slope, amount of erosion, drainage and pest management. Other options for producers using precision technologies may be small grids (two to five acres) or productivity zones based on soil differences. Individual samples would be submitted to the lab from each grid point/area or management zone. This data can be used to generate variable-rate fertilizer and seeding application maps. Regardless of what sampling method you use, some basic guidelines should be followed.
Sampling Guidelines
Consistency
- When sampling with a hand or hydraulic probe, carefully remove crop residue from the soil surface, then insert the probe (as straight as possible) to the desired depth.
- Take 10 to 15 samples from each management zone (or six to eight per grid) and mix thoroughly, as soils can be highly variable from one point to another.
- Sampling depth should be consistent from year to year so that nutrient values can be comparable over time.
Depth
- Sampling depth for the non-mobile nutrients (P, K, pH, OM, EC, zinc, iron, manganese, copper, and boron) is 0-6 inches. A deeper sample (0-24 inches) is recommended for mobile nutrients like NO3-N, chloride and sulfur.
- The best practice is to separate samples into two sub-sample depths, 0-6 inches and 6-24 inches. Keep in mind that deep samples (0-24 inches or, in some cases, over-vulnerable aquifers, 0-48 inches) must be taken if the field is a part of a concentrated animal feeding operation (CAFO) manure plan.
- In tilled fields, sampling prior to tillage operations is preferred for most-accurate results to ensure the correct sampling depth.
Submission
- Use a labeling system that works for you and the lab in which you intend to submit samples.
- It is best to air dry samples before mailing (do not use heat) or freeze and ship as quickly as possible, avoiding weekend layovers.
- For a list of known soil testing labs in and near South Dakota, view our Soil Testing Labs page.
Source : sdstate.edu