Obtaining a quality soil sample is vital for receiving accurate nutrient recommendations and achieving crop yield goals.
“In a 20-acre field, there is about 40 million pounds of soil,” said Sarah Kenyon, agronomy specialist with University of Missouri Extension office in Houston. “Of those 40 million pounds, you send one pound to the lab for results, so make sure that one pound represents the field.”
Soil samples need to be taken every three to four years. The average soil test assesses nitrogen, potassium, phosphorus, calcium, magnesium, organic matter, neutralizable acidity, cation exchange capacity and pH levels. Texas County Extension charges $17 per soil test.
Testing for micro-nutrients is not done unless the producer requests it at an additional charge. Micro-nutrients include zinc, sulfur, iron, manganese, copper, sodium, and boron. The fee ranges from $4-5 per nutrient and must also include a regular $17 test.
When soil sampling, be aware of previous management practices that can impact soil fertility. For example, if a pasture was once two pastures, separate samples should be taken on either side of the old fence line. Likewise, if there is high animal traffic in a pasture, that area should be sampled separately. Hillsides and waterways should be sampled differently. If a pasture has been converted to a crop field, separate samples need to be taken, or if a pond or tree line has been removed.
“Several samples bags need to be collected if the land is uneven,” Kenyon said.
When soil sampling, it is important to take samples at the same time of year to provide consistency and make proper year-to-year comparisons.
“It is best to wait at least three months after application of fertilizer, lime or manure before taking a soil sample,” Kenyon said.
Sample cores need to be four to six inches deep, because samples that are to shallow can cause an overestimate of soil fertility levels.
“Every core should be the same depth and quantity to provide uniformity,” Kenyon said.
A zigzag pattern of random soil sampling across the field works well in most situations. Be sure to avoid feeding areas, loafing areas around shade trees or ponds, or other areas of the field where animals congregate. The fertility in these areas is typically much higher than the rest of the field.
To collect a soil sample use a soil probe or auger; soil augers are available for use at the Houston MU Extension office. If you use a shovel, dig a hole and slice off one side. Individuals may even choose to use an electric drill to collect the soil sample.
“You can choose several different tools to do the same job,” Kenyon said. “The important thing to keep in mind is to collect the correct depth for each core sample.”
Kenyon recommends collecting 10 to 20 core samples in a bucket, and then crumbling and mixing them. Remove sticks, rocks and grass and place about one pint of soil into a plastic bag or soil sample box.
“The number of core samples collected should reflect the variation of the land and land history; more samples if the land is varied, less if it is more uniform,” Kenyon said. “It is better to take too many samples as opposed to too few.”
Grid soil sampling can also be used. This technique divides the field in 2.5 acres per samples. Grid sampling is economical when used in high yielding fields, especially when significant variations in soil tests are anticipated.
“It can also be useful in a field where the history is unknown,” Kenyon said. “Grid soil sampling provides the most accurate results when paired with a variable rate spreader.”
After collecting the soil take it to the nearest University of Missouri Extension county office. The staff there can help with the paperwork. The results should be returned in seven to 10 days.
Interpreting soil tests are the most difficult part of the process, but Extension specialists can make it easier. “Interpreting Missouri Soil Reports” is a guide sheet that can help individuals interpret their soil report. It is available at http://extension.missouri.edu/p/g9112.
Kenyon encourages farmers to call the Texas County Extension office with soil questions.
“When farmers call with questions about their soil report, I can give them recommendations specific to their farm and to their management goals,” she said.
Farm site visits can also be scheduled when necessary. Call the Texas County Extension office in Houston at 417-967-4545 or email Kenyon at kenyons@missouri.edu.
Texas County Extension agronomy specialist Sarah Kenyon advises that coring devices are best for soil sampling. Augers are recommended on rocky soils. Hand samplers at least three feet long are desirable because they reduce back strain. A power drill facilitates sampling in rocky or dry soils. Use a plastic container with a hole in the middle to collect the soil as the auger pulls it out of the ground. Empty the soil out of the plastic container into the soil sample bucket after each successful attempt to get a six-inch core.