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Soil Testing Sentinel Program in Minnesota

By Daniel Kaiser, University Extension Soil Fertility Specialist

With the extreme variability in growing conditions there have been some questions regarding the variability in soil test. A project is being launched to establish a series of sentinel plots to study the monthly variation in soil test values over the next two growing season. We are looking for participants that are willing to take samples from a single point within a field and mail them off to us at Saint Paul. The goal of this study is to gain a better understanding of what is happening over the growing season for a number of different nutrients commonly measured.

The study areas can be in any crop and can be previously fertilized with commercial fertilizer or manure.  However, I would like to know what was put on and when to gain a better understanding of variations between the locations.  The following is a general idea of the work involved in this project:

1) Select and geo-reference a field area with GPS in order to return to that site every 4 to 6 weeks when sampling is possible.
2) Collect about 2 lbs of soil in a fixed area around the sampling point.  Within a radius of 10 feet or less would be adequate.
3) Label the sample with location and sampling date and store in a lined or Ziploc bag and place in a refrigerator.
4) Send the samples off to the University.
5) If possible, hand harvest a small section around the sampling point.

Maintaining the samples in a cool place where the loss of moisture is critical.  Once we receive the samples they will be sieved and split into two samples, one will be air dried and sent off for analysis.  The second sample will be kept in a field moist state for analysis, One major component of this work will be to attempt to gain a better understanding of the variation of the potassium soil test over time.  The moist samples will help to determine if the difference between the field moist and dry potassium test warrants more research around the state of Minnesota.

Postage to send the samples off to me is available, or a pickup can be scheduled.  Compensation for travel to and from the sampling sites can be arranged. 

We also will have soil temperature sensors to install at the field locations.  Soil moisture will also be measured, but completed directly from the soil samples by taking weights before and after drying.  Moisture and temperature will be studied in order to determine if there is any link between differences in analysis before and after drying on the test themselves and on the variability in the soil test over time.

If interested, Please contact Daniel Kaiser via email ( or by phone at
612-624-3482. We currently are looking for up to 20 sampling locations to start by the end of 2013 to represent most of the major soil associations around the state of Minnesota..  

Specific details for the project can be found in the link below.

Soil Test Sentinel Plots.pdf

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  1. Dan,
    Are you coordinating other lab data with your trials. I think Agvise has several years of this type of data. Paul Groneberg


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