Soil Nitrate Testing
Why should you be concerned?
Nitrate testing of soil is an excellent and inexpensive way of evaluating the available nitrogen (N) status of your soil. MSU research and demonstrations have shown that many farmers could reduce their N fertilizer application rate on corn without risk of reducing yields if they used the soil nitrate test. Excess N fertilizer may increase nitrate contamination of groundwater.
Case Studies
We interviewed five Michigan farmers who recently used soil nitrate tests, with assistance from the Michigan Groundwater Stewardship Program (MGSP). Here is what they had to say about soil nitrate testing.
Why did you soil nitrate test?
- To decrease nitrogen leaching by avoiding over-application.
- To spread costs by not applying all the nitrogen, at one time.
- To determine if cover crops are recycling nitrogen.
- To save money.
How did you soil nitrate test?
- Many farmers hired a service to collect the soil samples.
- Soil nitrate testing instructions are given below.
How much did it cost?
- $10 to $18 per sample for labor and laboratory fees.
- The MGSP can cost-share up to 50% of the expenses.
Soil Nitrate Testing Instructions
- Soil samples can be taken in June after the soil has warmed up.
- Sample all fields where corn is to be planted. Manured and legume fields will likely contain the most nitrate.
- Soil-sample boxes for the soil nitrate are available from your MSU County Extension office.
- Each sample should be a composite of 15 to 20 soil cores taken from a uniform field no larger than 20 acres
- Take each core to a depth of 10 to 12 inches.
- Air-dry the sample immediately in a warm room. Do not hold wet samples in a plastic bag for any length of time.
- Take the sample to your MSU County Extension office for processing through the MSU Soil and Plant Nutrient Laboratory, or to a laboratory of your choice.
Economics of Nitrate Testing
The cost of soil nitrate analysis by the MSU lab is $7 per sample. Each sample should represent no more than 20 acres. Assuming it cost $6 to take the sample, the total cost is $13 per 20 acres or 65 cents per acre.
Reducing your N fertilizer rate by 5 pounds per acre on 20 acres will more than cover the costs of the test. Results from research and on-farm demonstration studies over the past five years indicate that nitrogen adjustments based on the test would return more than $5 per acre.