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Understanding Your Soil Test Report for
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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 two Example Reports step-by-step, review what is in the different parts of the reports, 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 Reports are in exactly the same format as the one you received in the mail from the University of Minnesota Soil Testing Laboratory. One example contains recommendations for an established perennial fruit crop, grapes, and the other example contains recommendations for three annual vegetable crops: sweet corn, cabbage, and tomatoes. The reports cover two very different situations and our discussion of them should be useful to you in understanding your own report no matter what type of crops you are growing. You will probably find it helpful to open the Example Reports now and print copies, so that you can refer to them as we go through their various parts. Example Soil Test Report - Grapes, Example Soil Test Report - Vegetables
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. In addition there is a separate document, "Notes for Horticultural, Turf, and Wild Rice Crops", that is sent to growers of these crops. The Notes pages list 16 additional comments that may be referred to by number in the same location in the RECOMMENDATIONS section as the Comments. For this exercise you can access the Notes pages and print copies to refer to at: Notes for Horticultural, Turf, and Wild Rice Crops
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 9 in the Grapes Report and 12 in the Vegetables Report, and the “Laboratory No.”, which is 11947899 in the Grapes Report and 18 in the Vegetables Report.
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 the Grapes Report “Organic Matter” has three stacked O’s, which tells you that the amount of organic matter is on the border between low and 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.
In the Vegetables Report “Organic Matter” has three stacked O’s, which tells you that the amount of organic matter is also on the border between low and medium in this soil. “Soluble Salts” were not measured, but there is a stack of seven H’s above “pH”, telling you that the soil is slightly alkaline. The “Buffer Index” was not measured for this sample, because it is determined 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 these soils. Once again, they refer to the categories just below them in the SOIL TEST RESULTS section. In the Grapes Report, there is a stack of ten P’s above phosphorus (Bray 1 Phosphorus), a stack of seven K’s above potassium, a stack of three Z’s above zinc, a stack of ten C’s above calcium, and a stack of three M’s above magnesium, indicating that the soil tested in the very high range for phosphorus, at the high end of the medium range for potassium, in the low range for zinc, in the high range for calcium, and near the medium level for magnesium.
In the Vegetables Report, phosphorus and potassium were the only nutrients tested. Two different tests were done for phosphorus, Olsen and Bray 1, but the Olsen Phosphorus test is the relevant one for this soil. The reason for two tests and selection of the Olsen P measurement will be explained in the next section - SOIL TEST RESULTS. The stacks of four P’s (above the Olsen Phosphorus box) and five K’s tell you that both phosphorus and potassium were low to medium in this soil. Interpretation of the relative phosphorus level is not straighforward, because there are three crops on this report and the stack of four P's refers to sweet corn. The relative phosphorus ranges for cabbage and tomatoes are different than the range for sweet corn, so the phosphorus level is actually in the very low range for cabbage and tomatoes. This difference between the crops is reflected in the P fertilizer recommendations on the report.
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 can be used in western Minnesota to determine nitrogen fertilizer recommendations for potatoes and sweet corn. Soluble salts and the rest of the plant nutrients listed on the report are most usefully tested for 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 Soluble Salts, Secondary Macronutrients, and Micronutrients sections in the University of Minnesota Extension bulletin Nutrient Management for Commercial Fruit & Vegetable Crops in Minnesota for more information on crops and soils where soil tests in addition to the Regular Series are recommended. Another useful nutrient management tool, especially for perennial fruit crops, is plant tissue analysis. Soil testing and plant analysis complement each other and are most effectively used in combination Plant Analysis. For vegetable crops, in-season monitoring of petiole/midrib nitrate-nitrogen can also be useful Tissue Nitrate Analysis.
At the far left of the RESULTS section is a box labeled “Sample/Field Number” which contains the identifying name or number you attached to the sample on the Soil Sample Information Sheet when you sent it to the laboratory. This is blank for the Grapes Report and is 1 on the Vegetables Report. The grape grower probably sent in only one sample and didn't bother to give his field an identifier. However, if you send in more than one sample it is critically important that you give them names or numbers and maintain a list of the sample identifiers you attached to each field.
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 the Grapes Report, 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 "Estimated Soil Texture" is also Medium for the Vegetables Report.
The rest of the categories in the RESULTS section are the numerical measurements of laboratory analyses that were performed on your soil sample. For the Grapes Report “Organic Matter” is 3.0%, “pH” is 5.5, “Buffer Index” is 6.5, “Bray 1 Phosphorus” is 45 ppm (parts per million), “Potassium” is 110 ppm, "Zinc" is 0.5 ppm, "Calcium" is 1500 ppm, and "Magnesium" is 70 ppm. For the Vegetables Report “Organic Matter” is 3.0%, “pH” is 6.0, “Bray 1 Phosphorus” is 4 ppm, "Olsen Phosphorus" is 6 ppm, and “Potassium” is 75 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 amount of soil organic matter is important, because it is one of the main factors determining nitrogen fertilizer recommendations. The higher the organic matter content, the lower the nitrogen fertilizer recommendation. This is because decomposition of organic matter and the associated release of plant-available nitrogen is a significant source of this nutrient for plants. Examples showing the effect of soil organic matter levels can be seen in the nitrogen recommendation tables for different crops in the University of Minnesota Extension bulletin Nutrient Management for Commercial Fruit & Vegetable Crops in Minnesota.
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 two boxes for phosphorus soil test results, "Olsen Phosphorus" and "Bray 1 Phosphorus", can also be confusing. The Grapes Report only has numbers in the Bray 1 P box, but the Vegetables Report has values for both Olsen P and Bray 1 P. As noted above in the INTERPRETATION OF SOIL TEST RESULTS section, the Olsen P measurement is the one used for the Vegetables Report. The reason for the difference in the two reports is that different laboratory methods are used to determine plant-available P, 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. The pH of the soil in the Vegetables Report is 7.6, so Olsen P is the appropriate measurement.
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 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 amounts 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. The two phosphorus tests discussed above, Olsen and Bray 1, provide an example of how different laboratory methods give results that have varying numerical scales. For many vegetables an Olsen P test of 28 ppm is high, but a Bray 1 P test of 28 ppm is medium.
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 Grapes Report it tells you Crop Before Last: Grapes and Last Crop: Grapes, which tells you that this is an established planting. This is important information for the Soil Testing Laboratory to know, because for perennial crops fertilizer recommendations are different for established plantings than they are for new plantings. In the Vegetables Report it tells you Crop Before Last: Sweet Corn and Last Crop: Cabbage. Cropping history is important in determining nitrogen recommendations when a legume is included in the rotation, because crops like peas, snap beans, alfalfa, and clovers will provide some nitrogen for the following crop Nutrient Management for Commercial Fruit & Vegetable Crops in Minnesota.
The first box on the left side gives the “Crop and Yield Goal”. The crop is Grapes, of course, on one report and on the Vegetables Report there are three crops listed that will be planted in this field: Sweet Corn, Cabbage, and Tomatoes. For sweet corn, a yield goal of 8 tons/acre is given. Yield goal is one of the factors used in determining N, P, and K fertilizer rates for some crops such as potatoes, snap beans, and sweet corn. Recommendations for many other vegetable and fruit crops are based on a single "approximate yield goal". These can be found in Nutrient Management for Commercial Fruit & Vegetable Crops in Minnesota. The "Crop and Yield Goal" box also gives a list of pertinent Comments and Notes following the label Comments. In the Grapes Report, numbers 3, 18, 24, 50, 53, and 64 are specified. In the Vegetables Report, numbers 4, 5, and 18 are specified for sweet corn and 18, 50, and 57 for both cabbage and tomatoes. We will discuss these Comments and Notes in the next section after we go through the lime and fertilizer recommendations for Grapes and Vegetables.
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. For annual crops this is done before planting and the fertilizer or lime is incorporated with subsequent tillage. Shallow incorporation is also possibe for some perennial crops that have cultivated row middles. Row/Drill refers to methods of placing fertilizer close to the seed at planting and it is practiced for some nutrients on some annual vegetable crops. Row placement means that fertilizer is placed in a "starter" band that is traditionally about 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, which is not relevant to the crops we are discussing here.
The following column is labeled “Lime #ENP/A” and in the Grapes Report the recommended rate is 2500 pounds of ENP per acre using a broadcast application. Lime is recommended for grapes because the soil pH is less than 6.0. For all three vegetable crops no lime is recommended, because the soil pH is already 7.6. 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 Grapes, 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” (pounds of nitrogen per acre) column label. For Grapes, the nitrogen recommendation is to broadcast 30 lb/acre. On the Vegetables Report the recommendations are: Sweet Corn - 150 lb/acre broadcast, Cabbage - 180 lb/acre broadcast, and Tomatoes - 130 lb/acre broadcast. The next two columns in the RECOMMENDATIONS section are labeled “P2O5 lb/A” and “K2O lb/A”. These give the fertilizer recommendations for phosphate and potash. Phosphate (P2O5) and potash (K2O) are the terms and chemical formulas used to express the amounts of phosphorus and potassium in fertilizer recommendations. The phosphate recommendations are 0 lb/acre for Grapes (since the soil test level was very high), 60 lb/acre broadcast or 35 lb/acre in the row for Sweet Corn, 150 lb/acre broadcast for Cabbage, and 150 lb/acre broadcast for Tomatoes. As described in the RESULTS section, phosphate recommendations for the Vegetables are based on the Olsen Phosphorus soil test measurement. Potash recommendations are 100 lb/acre broadcast for Grapes, 100 lb/acre broadcast or 40 lb/acre in the row for Sweet Corn, 200 lb/acre broadcast for Cabbage, and 200 lb/acre broadcast for Tomatoes.
The recommendations for Sweet Corn show that for this crop row application of phosphate and potash permits the use of lower rates that result in equivalent yields compared to higher rates of broadcast fertilizer. The effectiveness of reduced rates for row application has not been demonstrated for other vegetable crops. Row applications may be recommended as the most efficient method, such as for phosphate fertilization of potatoes, but recommended rates for row application are not lower than broadcast recommendations Nutrient Management for Commercial Fruit & Vegetable Crops in Minnesota.
After the primary macronutrients NPK are recommendations for secondary macronutrients and micronutrients. Zinc, calcium, and magnesium were tested for Grapes and no additional nutrients were tested for the Vegetable crops. Recommendations for Grapes are to broadcast 10 lb Zn/acre and 50 lb Mg/acre. No calcium is required.
The "Comments" listed in the RECOMMENDATIONS section refer to items on the second page of the Soil Test Reports we have been working through (titled "Comments"), as well as to items in a separate document we have already referred to: Notes for Horticultural, Turf, and Wild Rice Crops. Items on the Comments page are numbered 1-25 and items on the Notes pages are numbered 50-65. These Comments and Notes provide explanatory information that will help you apply fertilizer and lime effectively and efficiently. Be sure to read through the listed Comments and Notes and apply the ones that are appropriate to your situation.
As discussed above, Comment and Note numbers 3, 18, 24, 50, 53, and 64 are specified in the Grapes Report. Items 3, 18, and 24 are on the Comments page and items 50, 53 and 64 are on the Notes pages. Comments 3 and 24 discuss liming. Number 3 tells you that it takes 6-12 months for lime to react with the soil and raise pH to the desired level. Number 24 tells you how to calculate the actual amount of lime to apply in terms of the lime recommendation that is given in ENP units. Comment 18 gives information on subtracting the nutrients contained in manure applications from fertilizer recommendations. On the Notes pages, Number 50 talks about split applications of nitrogen on coarse textured soils to prevent nitrate leaching. The reported soil texture was medium, but comment 50 is listed in all fruit and vegetable reports in case your soil is somewhat sandy and drains readily. Several smaller nitrogen applications rather than a single large one will protect groundwater quality on sandy soils. Number 53 tells you to sidedress fertilizer in the spring for established perennial plantings and avoid winter damage by not applying nitrogen after June 30. Because this sample was tested for calcium, number 64 is listed and provides information on maintaining soil calcium levels and dealing with physiological calcium disorders that affect some crops.
Comment numbers 4, 5, and 18 are specified in the Vegetables Report for Sweet Corn and Comment 18 and Notes 50 and 57 are listed for both Cabbage and Tomatoes. Numbers 18 and 50 were described above for Grapes. Numbers 4 and 5 for Sweet Corn discuss the situation where low broadcast rates of only phosphate or potash are recommended and the option of doubling the rate and broadcasting in alternate years is suggested as a practical application method. Number 57 for Cabbage and Tomatoes recommends applying a starter solution high in phosphorus for vegetable transplants. More information on starter solutions can be found at the end of the "Phosphorus" discussion in the Primary Macronutrients section of the University of Minnesota Extension bulletin "Nutrient Management for Commercial Fruit & Vegetable Crops in Minnesota".
Hopefully this discussion has helped you understand the information contained in your Soil Test Report. If you have additional questions, contact:
| Peter Bierman 612-626-4986 pbierman@umn.edu |
or | Carl Rosen 612-625-8114 crosen@umn.edu |