|
OneStop | Directories | Search U of M |
 
      
Understanding Your Soil Test Report for
|
| Agronomic Crops | Horticultural Crops | Lawn and Garden |
The first step for a producer in accurately fertilizing a field is to collect a representative soil sample and send it to a laboratory for analysis. After completing the analysis, the laboratory sends the results back to you along with lime and fertilizer recommendations. The second step in accurate and efficient fertilization is to interpret the results correctly. Then you are ready to apply the necessary rates of fertilizer and lime to achieve optimum yields of your crops. The Soil Test Report from the University of Minnesota Soil Testing Laboratory is relatively straightforward, but it contains a lot of information and some technical terminology that can be confusing if you have limited experience using it.
The information that follows is designed to provide some simple guidelines you can use to effectively interpret your University of Minnesota Soil Test Report. The next section provides a list of definitions for technical terms and abbreviations used in the report. In the following sections we will go through an Example Report step-by-step, review what is in the different parts of the report, provide links to useful sources of related soil fertility information, and highlight the bottom line: what does the report tell you to do in your field?
B - the chemical symbol for boron
Bray 1 Phosphorus - a soil testing procedure that is used to determine the level of plant available phosphorus in soils with a pH of 7.4 or less
Buffer Index - a soil test measurement that is used to determine the amount of lime required to raise soil pH to the desired level; the buffer index is measured only when the pH of a mineral soil is less than 6.0
Ca - the chemical symbol for calcium
Cu - the chemical symbol for copper
#ENP/A - abbreviation for pounds of Effective Neutralizing Power per acre; ENP units provide a uniform way of expressing the lime requirement, because liming materials differ in their purity and particle size distribution and these characteristics determine their neutralizing capacity in the soil; the label on liming materials will tell you the pounds of ENP per ton of product
Fe - the chemical symbol for iron
K - the chemical symbol for potassium
K2O - see Potash
lb/A - abbreviation for pounds per acre
Mg - the chemical symbol for magnesium
mmhos/cm - millimhos per centimeter; a unit of electrical conductivity that is used to measure the relative concentration of soluble salts in the soil solution
Mn - the chemical symbol for manganese
N - the chemical symbol for nitrogen
Nitrate, NO3-N - a plant available form of nitrogen that occurs in the soil; nitrate is also readily leached through the soil
Olsen Phosphorus - a soil testing procedure that is used to determine the level of plant available phosphorus in soils with a pH greater than 7.4
P - the chemical symbol for phosphorus
Phosphate, P2O5 - the terminology and chemical formula used to express the amount of phosphorus required in a fertilizer recommendation and the amount of phosphorus in a bag of fertilizer
pH - a measurement of the acidity or alkalinity of the soil solution
Potash, K2O - the terminology and chemical formula used to express the amount of potassium required in a fertilizer recommendation and the amount of potassium in a bag of fertilizer
ppm - parts per million
SO4-S - sulfate, a plant-available form of sulfur that occurs in the soil
Soil Texture - the relative proportions of sand, silt, and clay particles in a soil, which determine the soil type (e.g. silt loam or clay loam)
Soluble Salts - ions (charged atoms or molecules) that are dissolved in the soil solution
Zn - the chemical symbol for zinc
The Example Soil Test Report is in exactly the same format as the one you received in the mail from the University of Minnesota Soil Testing Laboratory. It contains recommendations for corn, but our discussion of it will be useful to you in understanding your own report no matter what crops you are growing. You will probably find it helpful to open the example report now and print a copy of it, so that you can refer to it as we go through its various parts. Example Soil Test Report
The University of Minnesota Soil Test Report contains five sections that we will go through in the same order as they appear in the report:
The Header, INTERPRETATION OF SOIL TEST RESULTS, SOIL TEST RESULTS, and RECOMMENDATIONS sections are on the first page of the Soil Test Report . The Comments section is on a separate page and is included with the Example Report. It lists 25 explanatory comments that may be noted by number in the RECOMMENDATIONS section. If you are growing corn, you were also sent an information sheet New Nitrogen Guidelines for Corn Production in Minnesota that you will use to determine the nitrogen fertilizer rate that best fits your field and situation. We will not go through that information here, because the document itself outlines the procedure for using the new guidelines.
You will not see a "Header" title, but what we are calling the Header section is the general information at the top of the first page. This information is self explanatory, although we'll point out that on the lower right side is a column of five items that contains two numbers you will need to refer to if you find it necessary to call the Soil Testing Laboratory to discuss some aspect of your report. These are the “Report No.”, which is 11 in this case, and the “Laboratory No.”, which is 17.
At the far left of the INTERPRETATION section are definitions for the “Soil Texture Code”. The Code lists the soil types contained in the broad classifications of “Coarse”, “Medium”, and “Fine”. You will refer to the Soil Texture Code when the texture of your soil is classified in the SOIL TEST RESULTS section.
The next three columns in the INTERPRETATION section graphically illustrate the relative levels of organic matter, soluble salts, and acidity in your soil, along with the buffer index. The graphs use stacked letters to form bar charts and they refer to the categories just below them in the SOIL TEST RESULTS section. In this case “Organic Matter” has five stacked O’s, which tells you that the amount of organic matter is medium in this soil. “Soluble Salts” were not measured, but there is a stack of two H’s above “pH”, telling you that the soil is moderately acid. A category related to pH is the “Buffer Index”, which has four stacked B’s and tells you that the Buffer Index is just below the intermediate level or slightly acid. The Buffer Index is measured only if the pH of a mineral soil is less than 6.0.
The rest of the INTERPRETATION section is not separated into columns, but it follows a similar graphical format that illustrates the relative levels (from “very low” to “very high”) of plant nutrients that were tested for in this soil. Once again, they refer to the categories just below them in the SOIL TEST RESULTS section. In this case, there is a stack of five P’s above phosphorus and a stack of 6 K’s above potassium, indicating that the soil tested in the medium range for both of these major plant nutrients (P is the chemical symbol for phosphorus and K is the chemical symbol for potassium).
Soil texture, organic matter, pH, buffer index, P, and K are part of the Regular Soil Test Series and are the usual categories tested. The nitrate (NO3-N) test is a standard practice used to adjust nitrogen fertilizer recommendations for a variety of crops in western Minnesota and is used in some situations in other parts of the state; see Using the Soil Nitrate Test in Minnesota. Soluble salts and the rest of the plant nutrients listed on the report are tested for only under specific circumstances where a problem is suspected or likely to occur. These circumstances include certain soil types and crops which are more prone than others to develop deficiencies of specific nutrients. See the University of Minnesota Extension bulletin Fertilizer Recommendations for Agronomic Crops in Minnesota for more information on crops and soils where soil tests in addition to the Regular Series are recommended.
At the far left of the RESULTS section is a box labeled “Sample/Field Number” which contains the identifying number or name you attached to the soil sample when you sent it to the laboratory. This is 5 on the Example Report. If you sent in more than one sample, it is critically important that you maintained a list of the sample numbers you attached to each field. As noted above in the INTERPRETATION section, the categories reported in this RESULTS section are those in the Regular Soil Test Series.
To the right of Sample/Field Number is “Estimated Soil Texture”. Texture is determined by an experienced lab technician on the basis of how a moist soil sample feels when it is manipulated between the thumb and fingers. In this case, soil texture is classified as Medium and if you go up to the Soil Texture Code box in the INTERPRETATION section you will see this means that your soil is a loam or silt loam.
The rest of the categories in the RESULTS section are the numerical measurements of laboratory analyses that were performed on your soil sample. “Organic Matter” is 3.5%, “pH” is 5.5, “Buffer Index” is 6.2, “Bray 1 Phosphorus” is 10 ppm (parts per million), and “Potassium” is 90 ppm. If you want to know more about the laboratory procedures used to obtain these measurements, see Our Methods on the University of Minnesota Soil Testing Laboratory web site.
The organic matter level is one of the factors used to determine the nitrogen fertilizer recommendation for some crops. Soils with higher organic matter have lower nitrogen recommendations. This is because decomposition of organic matter and the associated release of plant-available nitrogen is a significant source of this nutrient for crops. Soil organic matter is not used in nitrogen recommendations for corn.
A soil test that is often confusing to people is the Buffer Index. The Buffer Index is used to determine how much lime is required when soil pH is too acid. The Buffer Index is only run if the pH of a mineral soil is less than 6.0. The box will be blank if the soil is organic or if the pH is 6.0 or higher. Soils differ in their buffering capacity, or ability to resist a change in pH, so soils with the same pH may need different amounts of lime to achieve a similar pH change. The pH measurement tells you whether you need to apply lime and the Buffer Index tells you how much lime will be required to accomplish the desired change in pH.
The numerical laboratory measurements are not very useful to many people, because unless you work with them a lot it is not clear what the numbers mean (except for pH). That is why the INTERPRETATION section comes first. Laboratory tests for the amount of plant-available nutrients are indexes of relative availability, rather than absolute measurements of availability, and different laboratory methods give results that have varying numerical scales. The INTERPRETATION section tells you whether the laboratory measurement is low or high in terms of the need for fertilizer application. If the soil test is low, it means that the crop is likely to respond positively to the addition of fertilizer. If the soil test is high, it means that additional fertilizer is much less likely to improve crop growth.
People often wonder why there are two boxes for phosphorus: "Olsen Phosphorus" and "Bray 1 Phosphorus". This is because different laboratory methods are used depending on the pH of the soil. For calcareous soils with a pH greater than 7.4, the Olsen test is used. If soil pH is 7.4 or less, the Bray 1 test is used. These two phosphorus tests provide an example of how different laboratory methods give results that have varying numerical scales. For corn an Olsen P test of 12 ppm is high, but a Bray 1 P test of 12 ppm is medium.
When the Olsen P test is run, there will be numbers in both the Olsen P and Bray 1 P boxes. This is because the Bray 1 test is initially run and its results are recorded on all soil samples. For samples with a pH above 7.4, the Olsen test is then run and that result is also recorded. If there are numbers in both the Bray 1 and Olsen boxes, the Olsen P value is always the one used for interpretation and P fertilizer recommendations. The soil test report for vegetables Example Soil Test Report - Vegetables on the Horticultural Crops page gives an example of a soil where the pH is 7.6 and the Olsen P test is used.
The RECOMMENDATIONS section gives you the bottom line: how much fertilizer or lime should you apply for optimum production of your crop. For some people, this may be the only part of the Soil Test Report that they are concerned about.
The first line of the RECOMMENDATIONS section gives the cropping history. In the Example Report it tells you Crop Before Last: Corn, Grain and Last Crop: Soybeans. Cropping history is important in determining nitrogen recommendations when a legume is included in the rotation. In this case for corn following soybeans, the nitrogen recommendation will be 30-35 lb/A (pounds per acre) less than it would be for corn following corn or most other non-legume crops. See Fertilizer Recommendations for Agronomic Crops in Minnesota for more information on nitrogen credits for previous crops
The first box on the left side of the RECOMMENDATIONS section gives the “Crop and Yield Goal”, in this case Corn, Grain and 120 bu./acre. Yield goal is no longer used in determining nitrogen recommendations for corn, but it is still used for phosphorus and potassium recommendations and is a factor in determining nitrogen recommendations for other crops. This box also gives a list of pertinent Comments. In this case, numbers 3, 5, 11, 18, and 24 are specified. We will discuss these Comments in the next section after we go through the lime and fertilizer recommendations.
The next column to the right of “Crop and Yield Goal” is labeled “Method” and gives two application options for the recommendations that follow: “Broadcast” and “Row/Drill”. Broadcast refers to spreading fertilizer or lime on the surface of the soil before planting and incorporating it with subsequent tillage. Row/Drill refers to methods of placing fertilizer close to the seed at planting. The term Row means that fertilizer is placed in a "starter" band that is traditionally two inches to the side and two inches below the seed. The term Drill means that fertilizer is applied along with small grain seed as it is planted with a grain drill. For more information on applying fertilizer close to the seed, see the University of Minnesota Extension publication Use of Banded Fertilizer for Corn Production.
The next column is labeled “Lime #ENP/A” and the recommended rate is 2000 pounds of ENP per acre using a broadcast application. ENP stands for Effective Neutralizing Power. Giving the lime recommendation in ENP units provides a uniform way of expressing the lime requirement, because there are a variety of liming materials on the market that differ in their purity, their particle size distribution, and their neutralizing capacity in the soil. The analysis on the label of a liming material will tell you the pounds of ENP per ton of the product. Crops differ in their optimum pH and liming rates differ accordingly. For corn, the lime requirement is designed to raise soil pH to 6.0. For more information on liming and liming materials, see the University of Minnesota Extension publications Lime Needs in Minnesota and Liming Materials for Minnesota Soils.
After lime is the “N lb/A” column label and for corn the recommendation box below it is left blank. This is because the recently updated nitrogen recommendations for corn require some inputs by the corn producer to tailor them to the unique situation of their field and farming operation. Nitrogen recommendations for corn are now based on the productivity potential of the soil, the ratio of the price of N fertilizer to the value of the crop, the producer’s risk tolerance, the previous crop, the nitrate-N soil test if it is recommended for your location or conditions, and manure applications. As mentioned above, if you are growing corn an information sheet New Nitrogen Guidelines for Corn Production in Minnesota was included with your Soil Test Report. Work through that sheet to determine the N fertilizer rate that best fits your field and situation. For additional information on the new N guidelines, see the University of Minnesota Extension publication Fertilizing Corn in Minnesota. For information on nitrogen fertilization of crops besides corn, see the sections on various other crops in Fertilizer Recommendations for Agronomic Crops in Minnesota.
The next two columns in the RECOMMENDATIONS section are labeled “P2O5 lb/A” and “K2O lb/A”. Phosphate (P2O5) and potash (K2O) are the terms and chemical formulas used to express the amounts of phosphorus and potassium in a fertilizer recommendation. The fertilizer recommendation for phosphate is 50 lb/acre broadcast or 25 lb/acre row/drill. The fertilizer recommendation for potash is 50 lb/acre broadcast or 30 lb/acre row/drill. Row (or band) application of phosphate and potash close to the seed permits the use of lower rates of fertilizer for some crops (corn, wheat, and barley) that result in equivalent yields compared to higher rates of broadcast fertilizer. Band application of phosphate and potash is especially effective when soil conditions are cold and wet at planting. For more information on phosphate and potash fertilization of corn, see the previously cited University of Minnesota Extension publications Fertilizing Corn in Minnesota and Use of Banded Fertilizer for Corn Production. For information on phosphate and potash fertilization of crops besides corn, see the sections on various other crops in the previously cited bulletin Fertilizer Recommendations for Agronomic Crops in Minnesota.
The “Comments” page is the second page of the Soil Test Report. As noted above, Comments 3, 5, 11, 18, and 24 were listed in the RECOMMENDATIONS section of the report. These comments provide explanatory information that will help you apply fertilizer and lime effectively and efficiently. Comment 3, for example, tells you that you should broadcast and incorporate lime 6-12 months before seeding to allow time for it to react with the soil and sufficiently raise pH for the next crop. Comment 5 says that when low rates of potash are recommended you can double the suggested rate and broadcast in alternate years. Comment 11 gives some precautions about fertilizer materials and rates when applying fertilizer in contact with the seed and Comment 18 talks about subtracting the nutrients contained in manure applications from fertilizer recommendations. Comment 24 also discusses liming and tells you how to calculate the actual amount of lime to apply in terms of the lime recommendation that is given in ENP units. Be sure to read through the listed comments and apply the ones that are appropriate to your situation.
Hopefully this discussion has helped you understand the information contained in your Soil Test Report. If you have additional questions, contact:
| Dan Kaiser 612-624-3482 dekaiser@umn.edu |
or | Peter Bierman 612-626-4986 pbierman@umn.edu |