Are your samples generating useful results?
Agronomy Bulletin 69 ─ Soil Sampling
Fertilizer programs should begin with accurate soil testing. Growers who can self-sample reduce costs and better understand their soil situations. Review best practices so your samples lead to more reliable results and more educated management decisions.
Factors to Consider
- Tools and equipment
- Choosing a laboratory
- Sampling technique
- Interpreting results
- Acquire the right equipment. The most common sampling tool is the soil probe. Soil probes are easy to use and most are graduated for gauging depth. If using a shovel, ensure you take an even vertical slice, rather than a wedge-shaped sample that over-represents the uppermost soil. Mix soil cores in a bucket to create a commingled sample for drying and mailing.
- Select a sampling technique. There are two types of sampling techniques: randomized and grid. Randomly collecting and mixing 15 to 20 soil cores from across a 10- to 20-acre field is the quickest way to create a sample. This removes bias that skews results. Grid sampling evenly distributes samples across the field to characterize variability. However, collecting several more samples is expensive and time-consuming. No matter the method, sample between former crop rows and avoid problem areas such as wet spots, fencerows or old burning areas, sampling separately if necessary.
- Adjust depth of sampling according to tillage. Conventional and minimum-till growers should sample at a 6-inch depth. No-till fields should be sampled at 2 inches deep for lime recommendations and at 4 to 6 inches deep for fertilizer recommendations.
- Sample in the offseason. Sampling right after harvest gives you more time to analyze data and develop a fertilizer plan. While there is no bad time to sample, labs often have a slower turnaround in the spring. Soils with optimal nutrient level should be sampled at least every three years or every time the crop is rotated.
- Choose a trusted laboratory. Various soil labs use different testing and recommendation methods. Pick a laboratory that you can rely upon for the long term. Compare cost, turnaround time and experience levels with your soil types. Also, find a lab that has an accredited quality control program. You do not have to use your agricultural university’s soil testing laboratory, since most states provide recommendations criteria at no cost. As long as you pick a private lab that uses the same testing methods, you can make your own recommendations. Follow the lab’s specific instructions for sample handling.
- Interpret the results. Raw data from a soil analysis are not helpful without recommendations for specific lime and fertilizer applications, which are calibrated from historical yield response and raw soil test data.
Quality soil samples generate accurate results to help you develop a profitable lime and fertilizer plan. For assistance with soil sampling and interpreting results, contact your local Mycogen Seeds customer agronomist or trusted agronomic adviser.