Ask an Agronomist

The answer will depend on the purpose of the sampling. Standard sampling for nutrients, soil pH, soil organic matter, and other common tests is usually to a 6-inch depth. In western areas, when sampling for soil nitrate, sampling to 2 or 3 feet is usually recommended. Some sampling purposes use a 1-foot depth.

It is important that a sufficient number of soil cores is taken to be representative of the area being sampled. Usually, 20-40 random cores are suggested as a minimum to represent a 40-acre field. For a small garden plot, 10-15 cores should be sufficient. The greater the variability in the soils of the area to be sampled, the more cores should be taken.

These are then thoroughly mixed together in a plastic bucket, then a subsample of about a pint of soil is sent to the lab. Use stainless steel or plastic sampling tools with no rust, corrosion, or other contamination. Samples should be refrigerated until shipping and be sent as soon as possible. Changes can occur in available nutrient levels if the sample is not processed expeditiously.

Typically, an agronomist will identify specific growth stages of particular crops to determine the rate at which they are progressing. Based on growing degree days (GDD) or heat units, we can also estimate what growth stage crops are at. The eKonomics Growing Degree Days calculator can help you estimate crop growth for specific areas within the US and Canada. Unfortunately, our data is limited to those geographies and crops based on availability.

Potassium issues are easily solved if sufficient potassium is applied, and it’s best if optimum soil-test potassium levels can be maintained. This helps avoid hidden hunger, optimizes N-use efficiency, and minimizes other stress. Take advantage of years with good crop prices and/or yields to invest in additional potassium.