The RECOMMENDATIONS section gives you the bottom line: How much fertilizer or lime should you apply for optimum growth of your lawn, garden, or landscape plants? For some people, this may be the only part of the Soil Test Report that they are concerned about.
The initial line of the RECOMMENDATIONS section tells you what type of plants the recommendation is for. In this example, we have one for a Home Lawn and one for a Vegetable Garden. Immediately below is an area between two solid lines that gives the actual amounts of lime and fertilizer nutrients to apply. Below that at the bottom of the page are additional instructions on how to select a fertilizer, application timing, and methods of application.
In the Example Home Lawn Report, the left side of the first line of the RECOMMENDATIONS tells you that the “LIME RECOMMENDATION” is 0 LBS/1,000 SQ. FT. (0 pounds of lime per 1,000 square feet), so liming is not recommended. On the right side of the first line it says “Grass watered Clippings removed”. This is information supplied by the client on the Soil Sample Information Sheet that accompanied the sample. The way a lawn is maintained is important because nitrogen recommendations for lawns vary depending on how the turf is managed. You can find more information on lawn care at Established Lawns and Turf, Nitrogen Recommendations (PDF). The next line says “TOTAL AMOUNT OF EACH NUTRIENT TO APPLY PER YEAR*” and below that are the recommendations for the three major nutrients: NITROGEN – 3 LBS/1,000 SQ. FT., PHOSPHATE – 0 LBS/1,000 SQ. FT., and POTASH – 3 LBS/1,000 SQ. FT. The asterisk at the end of the “TOTAL AMOUNT” line refers you to a “CAUTION!” statement below that discusses split nitrogen applications and slow release fertilizers to avoid burning the grass. This is followed by a schedule for split applications.
The terms phosphate and potash are used to express the amounts of phosphorus and potassium in fertilizer recommendations, as well as their percentages in bags of fertilizer. They are also frequently referenced by their chemical formulas, which are P2O5 for phosphate and K2O for potash.
The line below the total amount of nutrients to apply is the approximate NPK (Nitrogen:Phosphate:Potash) ratio of the fertilizer recommendation, which is 10-0-10. This ratio helps you choose a fertilizer that will be as close as possible to matching the recommendation. Fertilizer nutrient ratios and guidance for selecting fertilizers and application rates are located on the Explanation of Soil Test Report page. You can find a thorough discussion of fertilizers, rate calculations, and application methods at Inorganic and Organic Fertilizers (PDF), Slow Release Fertilizers (PDF), Fertilizer Grades (PDF), Calculating Fertilizer Rates from Soil Test Recommendations (PDF), Methods of Applying Fertilizers (PDF), and Yard Waste Compost Application (PDF).
Application of phosphorus fertilizer to established lawns in Minnesota is regulated by state law to protect water quality. Fertilizer containing phosphorus cannot be applied unless a soil test shows a need for additional phosphorus to maintain adequate fertility. Because this soil test does not demonstrate a phosphorus requirement, it is extremely important to select a fertilizer that contains no phosphorus (the middle number on the fertilizer bag is zero). For more information see Preventing Pollution Problems from Lawn and Garden Fertilizers (PDF).
Though not found in this example, some Home Lawn Soil Test reports contain recommendations for Sulfur. Most soils in Minnesota will not require sulfur fertilization for adequate grass growth, but coarse-textured soil with low organic matter is one situation in which sulfur may be deficient.
In the Vegetable Garden Report, the “LIME RECOMMENDATION” is 20 LBS/100 SQ. FT. The first thing to recognize is that lime and fertilizer recommendations for vegetable and flower gardens, as well as landscape trees and shrubs, are given for an area of 100 SQ. FT. This is different than the recommendations for the Home Lawn, which are based on an area of 1,000 SQ. FT. If you calculate your fertilizer rate using the wrong unit of area, you risk over- or under-fertilizing by a factor of 10.
Plants differ in their optimum pH levels and liming rates differ accordingly. For a Vegetable Garden, the lime requirement is designed to raise soil pH to 6.5. See Raising Soil pH (PDF) for more information on liming soils. Some plants, such as azaleas and blueberries, require acid soil and you may have to reduce soil pH for them to grow well. See Soil Acidification (PDF) for more information if you need to reduce soil pH. Information on the pH requirements of some common landscape plants can be found at Soil pH Preferences for Selected Landscape Plants (PDF).
The “TOTAL AMOUNT OF EACH NUTRIENT TO APPLY PER YEAR*” for the Vegetable Garden are: NITROGEN – 0.15 LBS/100 SQ. FT., PHOSPHATE – 0.2 LBS/100 SQ. FT., and POTASH – 0.3 LBS/100 SQ. FT. At the bottom of the page is a recommendation for mid-season application of additional nitrogen for certain vegetable crops. The approximate NPK ratio of this fertilizer recommendation is 15-20-30. The information section below the recommendations, the Explanation of Soil Test Report page, and the links embedded above in the Home Lawn discussion provide details on selecting a fertilizer, determining application rates, and choosing the best method of application.
If your Soil Test Report is for something other than an established lawn or a vegetable garden (eg. a flower garden, new lawn, trees, shrubs, or a fruit planting), it will follow the same format as the examples above, and the information presented here should be helpful. For information on fertilizing other types of plants, please refer to: Trees, Shrubs, and Fruits, Vegetable and Flower Gardens, New Lawns and Turf, and Tree Fertilization: A Guide for Fertilizing New and Established Trees in the Landscape (PDF).