Taking a good soil sample
Soil test analysis data collected from a field or garden can be no better than the sample. Therefore, proper collection of the soil sample is extremely important. Representative samples are as important to get good data back for those farming thousands of acres to those planting the home garden.
Soil tests can be submitted to a private soil testing lab or they can be submitted to the University of Minnesota Soil Testing Laboratory. Many local county extension offices have the submission forms and soil testing bags. The informational sheets are listed on the U of M Soil Laboratory Website: soiltest.cfans.umn.edu/ or you can directly contact the laboratory at (612) 625-3101.
Soil test data can provide data that indicates soil fertility, ph, and organic matter. Fertilizer recommendations are made corresponding to the soil test data. Common tests include phosphorus (P), potassium (K), organic matter, and pH. requirements. The most common fertilizer used for a fertility program is nitrogen. Nitrogen (N) is not tested for as often with a soil test due to nitrogen’s ever changing chemical forms in the soil.
Start by dividing the field/garden/lawn into areas that have the same soil color and texture, cropping history, and fertilizer, lime and manure treatments. On farmland and acreages, use of soil survey maps that indicate soil types, slope phase and erosion phase are useful because organic matter, nutrient levels and soil pH can vary following these map units. One sample should not represent more than 20 acres on level, uniform landscapes, or 5 acres on hilly or rolling land. Soil sampling using an intensive grid pattern of at least 2.5 acres in size is another option for growers working with a crop consultant or agricultural professional.
Sample each area for composite samples, which means you are pulling a large amount of samples and then you will condense. Within each area collect 15-30 sub samples (cores, borings, or spade slices) in a zigzag pattern throughout the designated field area. The more variable the soil, the more sub samples should be combined per area sampled. Scrape off all surface residues from the sub sample site.
Sample the soil to a depth of 6-8 inches (plow layer) for cultivated crops, or 3 inches for pasture, lawns or sod fields. Sample row crop fields between rows, except for ridge till plantings. Also avoid sampling dead or back furrows, terraces, old fence rows, lime or fertilizer spill areas, headlands, eroded knolls, low spots, or small saline areas. Sample at least 300 feet away from gravel or crushed limestone roads because their dust changes soil ph.
Mix the sub samples thoroughly in a clean plastic pail, and fill the sample box or bag to the fill line (1 pint). If the samples must be taken wet, they should be dried before being mixed and submitted to the Laboratory. Do not exceed a drying temperature of 97F, and do not use a microwave unless only the nitrate test is requested.
While different soil testing laboratories may offer different soil test options the procedures for conducting the actual tests tend to be similar. Contact the McLeod County Extension at 320-484-4303 or Meeker County Extension at 320-693-5275 for availability of submission forms, sample bags, and soil testing interpretations.