By MU Extension Agronomist Jill Scheidt
Obtaining a quality soil sample is vital for receiving accurate nutrient recommendations for your field.
“In a 20 acre field, there are 40 million pounds of soil. Of those 40 million pounds, you send 1 pound to the lab for results,” said Jill Scheidt, an agronomy specialist with the University of Missouri Extension.
Soil samples need to be obtained every 3-4 years; sampling costs range anywhere from 14-20 dollars depending on where you go and which nutrients you want to test. The average soil test assesses nitrogen, potassium, phosphorus, calcium, magnesium, organic matter, neutralizable acidity, cation exchange capacity and pH levels. Micro nutrients are not tested for unless the producer requests it at an additional charge.
Different soil types and soil needs are in the same pasture or field. Several samples bags need to be collected if the land is uneven. For example, if a pasture was once 2 pastures, separate samples should be taken on either side of the old fence line. Hillsides and waterways should be sampled differently as well. If a pasture has been converted to a crop field, separate samples need to be taken if a pond or tree line has been removed.
Sample cores need to be at least 6-8 inches deep. Every core should be the same depth and quantity. If using a shovel instead of a soil probe, dig a hole and slice off one side. Collect 10-20 cores in a bucket, crumble and mix them well. Then remove sticks, rocks and grass and place about one pint of soil into a plastic bag or soil sample box. Always label the bag in reference to where the sample was taken.
Interpreting soil tests are the most difficult part of the process. The first section of the soil test represents the current level of nutrients. Macro nutrients are expressed in pound per acre and micro nutrients are expressed in particles per million (ppm) and rated on a scale of very low, low, medium, high, very high, to excessive.
The lower section is the recommended additions of the nutrients expressed in pounds per acre according to the desired yield goal. Limestone tonnage recommendations can be calculated by dividing the Effective Neutralizing Material (ENM) by the guarantee of the limestone dealer. ENM guarantees are usually 400-450.