The MSU Extension Soil Fertility program has published two reference sheets on getting a good soil sample and the questions that need to be answered before a sample is sent off for laboratory analysis.
Clain Jones, Extension soil fertility specialist and professor in the Department of Land Resources and Environmental Sciences, said MSU soil fertility guidelines are based on spring soil sample results. Spring sampling is ideal because spring levels are more indicative of growing season nitrogen availability, compared to fall nitrogen levels.
Spring sampling can be more difficult than fall sampling, however, Jones suggested a few samples be taken in the spring, especially on soils less than 2 feet deep and those with greater than 60 pounds of nitrogen per acre last fall.
He said the effort put into getting soil samples from the right depth, time and location is rewarded by valuable soil test results.
“By tracking overwinter nitrogen losses or gains for given fields and rotations, producers are better able to predict future spring nitrogen levels from late fall soil samples and avoid over- or under-fertilization,” he said.
Sampling depth is another important consideration. Most nutrients and soil characteristics are determined from zero to 6-inch soil samples. Nitrogen for annual crops should be determined from samples taken 2-3 feet deep. Hay and pasture fields are usually sampled to 1-foot depth.
The soil analyses that should be requested may vary depending on whether the prior crop had growth problems or if the soil is showing issues like crusting. Jones suggested reviewing last season’s growth issues, which could indicate analyzing for something extra, such as cation exchange capacity or pH in the upper 3-inches, if acidity is suspected.
“We also list the specific soil analyses required by the Natural Resources Conservation Service if producers are involved in programs such as the Environmental Quality Incentives Program,” Jones said.
There are many other decisions made in the soil sampling process, such as which lab should be used and which test is best for soil phosphorus. Jones said it’s easy to forget a step in getting a good soil sample or to forget the answer to an important question about the sample or the field it came from.
“We’re providing these reference sheets to help anyone involved with soil sampling get the most value,” Jones said.