Interpretation of Soil Test Results (Lawn & Garden)

The INTERPRETATION section of your Soil Test Report focuses on four of the basic test results (Phosphorus, Potassium, pH, and Organic Matter) and represents them in graphical format.  A short explanation of how to read the graphs is 2/3 of the way down the left-hand column of the Explanation of Soil Test Report page.  The bar graphs use letters and symbols to fill the bar and the scale along the bottom provides context. 

For the Example Home Lawn Report, the phosphorus bar is filled with P’s showing that this soil tested very high for plant-available phosphorus using the Olsen P method. The bar of K’s for potassium extends out to the medium level and the asterisks for pH show that it is above the optimum level for a lawn and is slightly alkaline. Soluble salts were not tested, so that graph is blank.

For the Example Vegetable Garden Report, the phosphorus bar is about half-filled with P’s showing that this soil tested medium to high for phosphorus. The bar of K’s indicates that potassium is at the medium level, the asterisks for pH show that it is moderately acid and a little below optimum for many vegetables, and the asterisks for “Soluble Salts” show that salts are low and in the satisfactory range.

One of the Soil Test Results that is not shown in the Interpretation section is Sulfur for the Home Lawn sample, so we will have to wait for the RECOMMENDATIONS section to see its impact.  Another result not shown is Organic Matter, but an interpretation of organic matter levels and a short discussion of the importance of organic matter is provided on the Explanation of Soil Test Report page.  The Home Lawn, with 2.8% organic matter, is classified as Low.  The Vegetable Garden, with 3.5% organic matter, is classified as Medium.  The amount of soil organic matter is one of the main factors determining nitrogen fertilizer recommendations for many plants.  The higher the organic matter, the lower the nitrogen recommendation.  This is because decomposition of organic matter and subsequent release of plant-available nitrogen is a significant source of this nutrient for plants.  Examples showing the effect of soil organic matter level can be seen in the nitrogen recommendation tables for different types of plants in Soil Test Interpretations and Fertilizer Management for Lawns, Turf, Gardens, and Landscape Plants.

The Explanation of Soil Test Report page also has brief discussions of soil pH, buffer index, soluble salts, lead, and other special tests.  For more information that will help you interpret your Soil Test Results see Soil pH Modification (PDF), Overview of Essential Nutrients (PDF), which includes information about Nitrogen, Phosphorus, and Potassium results.