Can We Get More Information From Our Soil Samples?

A soil test is a profitable investment to inform our nutrient management strategy. Some farms find value in increasing sampling frequency (every one to two years) and intensity with more samples per field (0.5 versus 2.5-acre grid). Another possible way to increase the value of soil sampling is to consider additional tests that can provide helpful management information. Some examples are soil health, soybean cyst nematode, and corn nematode testing.

Depending on the lab we use, some tests may be available by checking a box on the lab input form. Sample collection costs may be minimal if we need a separate sample for a specific analysis. For example, depending on how we collect the nutrient soil sample, we often collect more soil than what will fit in the lab bag. Rather than tossing the excess soil back in the field, we can put it in a second bag. If the soil volume is not enough to split for a second (or third) analysis, we can collect additional cores.

There is a wide range of available soil health measures. The Soil Health Institute did a broad ranging analysis of 30 soil health test. SHI recommends a minimal suite of three measurements to be widely applied across North America (and likely beyond). Those measurements include: 1) soil organic carbon concentration, 2) carbon mineralization potential, and 3) aggregate stability. 

We have recently updated our guidelines for choosing a soil nutrient lab to include information on nutrient testing and soil health measures. Common nutrient and soil health terms are described. Plus, a listing of labs and services they offer is shown. Find the fact sheet at https://ohioline.osu.edu/factsheet/anr-0107  The list here focuses on a few of the more common tests available from labs in our region.

  • Active organic matter (POXC). Measures the portion of organic matter most likely to interact with plants and fertility.
  • Solvita test. This soil respiration test measures the soil's biological activity.
  • Haney test. This test measures how hospitable soil is for microbial life. Tests include measuring soil nutrients available to soil microbes, soil respiration (microbial breathing), water-soluble organic carbon, organic nitrogen, C:N ratios, and NO3, NH4, and other key nutrients. The results indicate the amount of food readily available to soil microbes and is sensitive to measuring root exudates and decomposed organic material.
  • Bulk density and aggregate stability. These laboratory tests measure soil structure and compaction.
  • Soil texture (or particle size analysis). A measurement of the amount of sand, silt, and clay in your soil, which dictates soil type.

 

Soybean cyst nematode (SCN) testing

Active management of Soybean Cyst Nematode (SCN) begins by knowing if you have the problem. Until the end of September (beginning of October for late planted soybean fields) you can scout fields and carefully dig out root to check for the presence of SCN. In addition, a composite soil sample will reveal the presence (or not) of SCN in your field, but most importantly, it will tell you the levels of SCN (Know your numbers!), which will help you select the best SCN management approach. You can collect soil sample for SCN test any time (i.e., in fall after harvest, spring before planting, or during the growing season).

As we mentioned above, the same composite sample collected for soil analysis can be divided into a subsample for SCN testing. Remember that nematodes are alive, and we want them alive until samples are processed. Therefore, samples must be protected from heat and direct exposure to sunlight until they are shipped to the lab. Find details about how to sample and where to send your SCN samples here.

Furthermore, with funding from Ohio Soybean Council and The SCN Coalition, growers may submit up to two soil samples to the Soybean Pathology and Nematology Lab, and we will test them for SCN free of charge.

 

Corn nematode testing

Several nematode species can negatively impact corn production (Fig. 1).

Corn field affected by plant-parasitic nematodes

Sampling for corn nematodes is slightly different than sampling for SCN. For example, we do not recommend collecting samples for corn nematode analysis in the fall. We must sample during the growing season to determine the relationship between nematode levels and potential damage to corn. Only corn fields showing symptoms [chlorotic and stunted plants, swollen and poorly developed roots (Fig. 2), etc.], specially under nutrient availability, should be sampled for corn nematodes.

Corn root affected by stubby-root and lesion nematodes

Samples can be collected when symptoms start appearing during the season. Up to corn growth stage V6, soil and root samples must be collected for corn nematode analysis. Collect a composite soil sample from the transition zone, the area between symptomatic/damaged plants and healthy ones. Using a shovel, collect plants with their roots from the transition zone. Place these roots in well-labeled plastic bags for shipping. Between corn growth stages V6 to R3, only composite soil samples should be collected. For corn growth stage R4 and beyond, we do not recommend sampling because the nematode levels are variable and not consistent with potential damage to corn. Keep in mind that nematode samples are alive, therefore, you must handle it carefully. To keep the nematodes alive, store your samples in a cool, dark place out of direct exposure to sunlight and ship them to the lab as quickly as possible.

 

Final considerations

Yield or past soil test results should drive sample area size decisions. A single sample should not represent more than 25 acres. Grid or zone sampling often results in zone sizes of two to twelve acres and target lime or nutrients to areas of greatest need. Sample depth should be consistent. For sample depth, our Tri-State Recommendations use an 8-inch sample core. Mark your probe at your selected depth. Throw out and take another sample core when cores are compacted in the probe. We like to blame the lab for bad samples, but we generally see more variability in the sample collection process than laboratory procedures for nutrient analysis. If you want more information on soil sample collection procedures, see the factsheet at https://go.osu.edu/soilsample .

 

Crop Observation and Recommendation Network

C.O.R.N. Newsletter is a summary of crop observations, related information, and appropriate recommendations for Ohio crop producers and industry. C.O.R.N. Newsletter is produced by the Ohio State University Extension Agronomy Team, state specialists at The Ohio State University and the Ohio Agricultural Research and Development Center (OARDC). C.O.R.N. Newsletter questions are directed to Extension and OARDC state specialists and associates at Ohio State.