Interpreting Your Soil Test Report — For Farmers

Targeted to farmers or producers of crops grown

over a large area – units in pounds per acre

Step 1: Do you need lime?

The most important information the soil test provides is based on the pH of the soil. If your pH is too low for the crop you are growing, we will make a lime recommendation. The sample soil test report recommends 2.5 tons of lime per acre. This application should come before any fertilizer is added (preferably about 2 months) to allow the liming material to raise the pH to an optimal level for your crop. If your sample does not have a lime recommendation, move on to the next step.

Step 2: Calculate the amount of fertilizer required

The nitrogen recommendation in the sample soil test report calls for 80 pounds per acre. Suppose you want to use urea (46 percent nitrogen). First, convert the percentage of the nitrogen source (urea) to a decimal (46 percent = 0.46). Now, divide into the recommended amount listed on the report: 80 ÷ 0.46 = 174 pounds of urea per acre.

The same approach for calculating nitrogen can be used for phosphorous and potassium. If you are using triple superphosphate (TSP) at 46 percent P205, convert to a decimal (46 percent = 0.46) and divide into the recommended amount listed on the report: 40 ÷ 0.46 = 87 pounds of TSP per acre. If you are using muriate of potash (60 percent K₂O) to provide potassium, first convert the percentage to a decimal (60 percent = 0.6). Next, divide into the recommended amount: 80 ÷ 0.6 = 133 pounds of potash per acre. 

Additional Information

The second page of the soil test report contains additional details about your sample. Units for elements tested are in pounds per acre (ppa). Of particular interest are phosphorous and potassium: green bars indicate additional fertilizer will probably not result in additional plant growth or yield; yellow bars indicate a plant response may or may not occur; and red bars indicate additional fertilizer will likely result in increased plant growth or yield.

What about nitrogen measurements? Plants require specific forms of nitrogen that are tricky to measure in the lab. Additionally, nitrogen is so mobile in the soil, measurement of current values would not be very helpful for predicting a nitrogen recommendation. Therefore, MSU Extension recommendations are based on research.

The information given here is for educational purposes only. References to commercial products, trade names, or suppliers are made with the understanding that no endorsement is implied and that no discrimination against other products or suppliers is intended.

Publication 3824 (POD-10-22)

By Keri Jones, Laboratory Coordinator, Plant and Soil Sciences.