Interpreting Soil Test Results for Gardens and Grounds
By Bruce Hoskins, Assistant Scientist of Plant, Soil, and Environmental Sciences, University of Maine. Reprinted with permission.
Uses and Limitations of a Soil Test
Soil testing is a quick and inexpensive way to determine the nutrient status of your soil. It helps to determine how much (if any) lime, fertilizer, or other amendments are needed to optimize your soil for plant growth. The first step in understanding the information you are receiving and how you can best use it, is to understand the limitations of the system.
Soils, even in a uniformly cultivated field or garden plot, are extremely variable. Because of this, one of the most important steps in soil testing is taking a good representative sample. Sample boxes and Field and Soil Sample Information forms are available, free of charge, on request from the lab or from any county office of Cooperative Extension. Sampling instructions appear both on the box and the form. These instructions should be followed closely, to ensure that the sample you send to the lab is representative of the whole area sampled. This is the single most important step you can take to make sure the system works for you.
Soil fertility testing should ideally provide consistent, reliable analytical results as quickly as possible. At the Maine Soil Testing Service, we use standardized mass-production procedures giving reproducible results with a minimum of sample handling. This system, monitored by a quality assurance program, provides accurate results in the shortest possible time. However, if you believe there is an error in your test results, call the Maine Soil Testing Service for a free of charge repeat analysis. We store samples for at least one month after testing.
A routine Standard soil test consists of measuring soil nutrients or other components which most commonly limit plant growth or production in Maine: phosphorus, potassium, calcium, magnesium, sulfur, micronutrients, pH, and organic matter. Nitrogen is also a common limitation to plant growth, but can be accurately tested only during the growing season (late May to late August), as part of a Comprehensive soil test.
Additional tests such as sodium, total soluble salts, or texture are available for an extra charge and must be specifically requested. Micronutrients (copper, iron, manganese, zinc) are not commonly deficient in Maine garden soils, but can be limited by improper soil pH or organic matter levels. Actual micronutrient deficiencies are often better diagnosed through plant tissue testing on those crops which warrant the extra expense.
The recommendations sent back to you for lime, fertilizer, or other amendments are designed to adjust soil nutrients and other components to a theoretical optimum level for best yield and quality from the crop you plan to grow. These optimum nutrient levels have been determined by greenhouse and field trials in Maine and other northeastern states. In this way the soil testing system is calibrated specifically for Maine soils and cropping conditions. It is further modified with experience in the field, feedback from growers and gardeners, and as new research information becomes available.
Soil testing is not the answer to all problems in growing a crop or in maintaining a healthy yard and garden. Poor plant growth or loss of yield may also be caused by insects, diseases, weed competition, pesticide residues, or excessively wet or dry conditions. When done properly, soil testing is a useful and economical tool for managing crop plant nutrition.
All the important background information pertaining to your sample appears at the top of the report form. Next to the printing date is the lab number (lab no.). All reference to this sample in our records keys on this number. When referring to your sample for billing purposes or problems with analysis, always reference the lab no. After the lab no. is the field or plot name which you gave to the sampling area. Record keeping is greatly simplified by using a consistent or permanent naming system for all your fields or plots, making it easier to follow nutrient levels over the years and to better monitor your soil fertility program.
Relative Soil Nutrient Levels
The test results for your soil are first presented as a series of bar graphs meant to help you visually interpret the actual numerical results which appear at the bottom of the report. Each graph is calibrated so that the ideal level for pH, organic matter, and each of the nutrients falls in the area under the “OPTIMUM” label. The meaning of each of the interpretation levels follows.
LOW — a nutrient, organic matter, or pH level listed as “low” has a high probability of limiting plant growth and yield. A recommendation will be made to substantially increase the level of this component in your soil. If the level is very low, several years of corrective fertilizing or liming may be necessary to achieve an optimum soil level. Close monitoring by yearly soil testing is suggested in this case. Banding of fertilizer near the row becomes critical at this test level to ensure efficient use and maximum nutrient availability within the rooting zone of the crop.
MEDIUM — a soil level listed as “medium” may be adequate for some low-demand crops in some cases. This is taken into account in the recommendations for those specific crops. A medium nutrient level may limit plant growth or yield by the end of the growing season or in years of very good growing conditions. Corrective fertilizing or liming is usually recommended in moderate amounts to cause a small increase in soil test level after the crop has been removed or to support an exceptional yield in a very good year.
OPTIMUM — a soil component listed as “optimum” is in the theoretical ideal range to support plant growth and to maximize yield. Corrective fertilizing is not recommended. Any amendments recommended for a component listed as “optimum” are to compensate for crop removal, so that this optimum level can be maintained from year to year. A small amount of a starter fertilizer containing this nutrient may also be recommended. When all nutrients fall in the optimum range, competitive interactions between nutrients are minimized. This is especially important with calcium, potassium, and magnesium, which can compete with each other for binding sites in soil and uptake into plants.
ABOVE OPTIMUM — An above optimum soil test level indicates a level higher than needed to support normal plant growth. Growth and yield may be inhibited, either because of direct toxic effects to plants or because the overabundance of one nutrient may interfere with the uptake or availability of others present at very low levels. Additional application of nutrients or other components present at an above optimum level will only increase the likelihood of reduced yield. There will be no recommendation for further additions of this component in almost all cases. One exception is the optional application of a very small amount of starter phosphorus on some crops to compensate for cold soils in the spring. Crop removal and other natural losses over time should eventually reduce the nutrient, pH, or organic matter level to optimum after a few years.
Below the Relative Nutrient Level bar graphs is a line stating the name of the crop for which you have requested recommendations. Check this carefully to be sure this is the crop you are intending to grow or the closest one listed on the Field and Soil Sample Information form. Be sure the crop code listed is for the correct growth stage or management situation. There are different crop codes for seeding vs. topdressing hay and turf crops. There are also different crop codes for new vs. established beds for some vegetable and fruit crops. The crop code is the key for all the recommendations that follow. If it is incorrect, write, call, or email the Maine Soil Testing Service to receive a corrected report form.
Following is a general overview of the recommendations for all crops. Greater detail on calculating specific nutrient requirements for all crops can be found in the “Soil Testing Handbook for Professional Agriculturalists,” which is also available on our website (http://anlab.umesci.maine.edu).
The lime recommendation is the amount needed to raise the current soil pH to the optimum level for the crop being grown. This should be the same pH listed in the pH management statement in the Laboratory Results section (see below).
The lime recommendation is based on the assumption that the lime is rated at 100% calcium carbonate equivalence (CCE), a measure of the neutralizing power of the lime. If the lime you are using is guaranteed for less than 90% CCE, you should increase the application rate accordingly.
Lime recommendations for more than one target pH are listed for some crops to make allowances for alternate management practices. Cation exchange capacity calculations are based on only one target pH in any case (see Cation Exchange Capacity, below). If the lime requirement to reach a target pH is more than 125 lb per 1000 sq. ft., a split application will be recommended over two or more years to adjust the pH gradually and avoid possible nutrient balance problems. If lime is to be topdressed, application should be limited to 100 lb per 1000 sq. ft. in any one year.
Lime is also the primary source of calcium. An optimum pH should automatically result in an adequate calcium level if the pH has been adjusted using lime. The lime recommendation is usually the only recommendation made to adjust the soil calcium level.
***IMPORTANT NOTE: If you have applied lime or liming material within six months prior to taking your soil sample, it probably has not yet completely reacted. The soil pH level that we report to you should continue to rise, even without further lime application. To correct for this, subtract any recent lime application from our lime recommendation(s) and apply only this reduced amount.
A sulfur recommendation is made in place of lime when it is necessary to acidify or lower the soil pH. Acidifying the soil is necessary to avoid nutrient availability problems, especially with micronutrients, in those situations where the soil pH exceeds 7.0. Sulfur is also recommended for acid loving plants where soil pH is above the 4.8 – 5.2 range. Sulfur can be applied to acidify soil either as elemental (yellow) sulfur or by using aluminum sulfate at six times the rate recommended for yellow sulfur.
Lesser amounts of sulfur may be recommended, as a nutritional supplement, when the sulfur test level is low or medium. See additional information on sulfur nutritional amendments in the Laboratory Results section.
Magnesium is recommended if the present soil level is below 15% saturation. Saturation levels are explained in the Lab Results section below. The most common and most economical source of magnesium is magnesium lime or dolomitic (high-magnesium) lime. Quite often when lime is not needed, no magnesium recommendation is made. Cases of acute magnesium deficiency are quite rare and the cost of other sources of this nutrient is often prohibitive. In most cases, it is acceptable to wait until lime is needed again and to then apply a magnesium lime. In some cases, other sources of magnesium are recommended. These are suggested if cost and availability are not a problem in your area.
The nutrient levels in the Laboratory Results section (below) are reported in simple elemental form (P, K, etc.). However, the guaranteed nutrient content of all commercial fertilizer blends is reported by law as a three number code in terms of percent N (nitrogen), percent P2O5 (phosphate), and percent K2O (potash) regardless of the actual chemical form of the nutrient carrier(s) in the blend. Note that phosphate and potash are expressed in a molecular form and not in simple elemental form. The recommendations you receive for these nutrients have been adjusted to be in the same terms as those in the fertilizer code.
Because of ample rainfall in the eastern U.S., there is not an acceptable year-round soil test to predict the amount of nitrogen that will become available to plants over the course of a growing season. A soil’s nitrogen supplying capacity depends on the microbial breakdown of organic matter and the conversion of the nitrogen in organic matter to the ammonium and nitrate forms (called mineral nitrogen). Since this conversion process depends on the highly variable factors of soil temperature and moisture, it is very difficult to predict. Nitrate nitrogen is the form most commonly used by plants, though some can use ammonium nitrogen for part or all of their requirements. Nitrate is also the most easily leached of all nutrients, since the soil has almost no capacity to hold it. Measurements of mineral nitrogen are most meaningful during the growing season, but not during early spring or late fall sampling periods.
The baseline nitrogen recommendation you receive is usually based on the full seasonal requirement needed to support high yield from the requested crop. Then adjustments to the baseline recommendation are made for a variety of different situations. For instance, a home garden soil with an optimum organic matter level should provide most of the nitrogen needed over the next growing season. Home gardeners are reminded to reduce the recommended nitrogen accordingly. Additional information on nitrogen adjustments and nitrogen fertilizer application appear below in the Management Recommendations section.
The phosphate requirement is calculated by subtracting the present test level from the optimum soil level for the crop you will be growing and converting from P to P2O5:
Phosphate requirement = (optimum P – present P) x factor
The factor converts from the soil level (reported as P) to fertilizer content (reported as P2O5) The factor also compensates for the partial loss of applied phosphorus to unavailable forms.
A small amount of phosphate may be recommended, even at above optimum soil test levels, as a starter fertilizer. It is meant to promote early root growth and to compensate for limited P availability while the soil is still cold. In most cases, an above optimum soil test level of phosphorus will result in a recommendation for no additional phosphate amendments. Optional phosphorus applications should be avoided if the application area is near a stream, lake, pond, or in a phosphorus-sensitive watershed.
At a very low P test level, the phosphate recommendation may be limited to a maximum amount. This is meant to raise the soil level gradually, prevent possible burn from excess fertilizer salts, and spread the extra cost over more years. Because of this limit, soil phosphorus may not be adjusted to the optimum level during the first year. Additional corrective applications may be necessary in subsequent years.
The potash recommendation is calculated to raise the soil level from the present (percent saturation) test level to the optimum percent saturation for the crop to be grown:
Potash requirement = (optimum % K sat. – present % K sat.) x CEC x factor.
The factor in this case serves two functions. It converts from the soil level (reported as K) to the guaranteed fertilizer content (reported as K2O). It also includes the conversion factor from milliequivalent (percent of CEC) level to pounds per 1000 sq. ft. CEC and percent saturation are explained in the Laboratory Results section.
If the potassium level in the soil is above optimum, no further potash amendments will be recommended. The exception to this is a small amount of potash recommended on low CEC soils for heavy potassium feeding crops, when the total quantity of available K is less than 250 lb/A.
At very low potassium test levels or for very high CEC soils, the potash recommendation may be limited to a maximum amount. This will raise the soil level gradually, prevent burn from fertilizer salts, prevent localized nutrient imbalance problems, and spread the cost over more years. Because of this limit on application, soil potassium may not be adjusted to the optimum level during the first year. Additional corrective applications may be necessary in subsequent years.
Small area recommendations
For all situations that typically involve less than one acre, recommendations for nutrient amendments are given on a 1000 square foot basis or in some cases on a 100 square foot basis. For chemical recommendations, we will also suggest a rate of one of the common grades of pre-mixed commercial fertilizer. Unfortunately, the common grades do not always fit the calculated requirements for each nutrient. The grade with the closest fit to the calculated requirements will be recommended and the application rate adjusted to match the nitrogen requirement.
Gardeners who use chemical fertilizers are given a choice between using a common commercial blend or mixing their own out of single nutrient carriers. If you choose to mix your own fertilizer, keep in mind that the ingredients listed are more concentrated than most fertilizers you commonly use. Ingredient weights and application rates should be followed closely. The benefit of mixing your own is that the calculated nutrient requirements are more accurately met. Since over-application of any one nutrient is avoided, it may also be more economical in the long run.
Recommendations for organic farmers and gardeners are made using nutrient sources that have not been chemically processed or derived. Each of the organic amendments suggested are a good, consistent source of at least one or two of the major nutrients. Application rates of these materials meet calculated N, P2O5, and K2O requirements. Rates of some organic amendments are adjusted to reflect the slower nutrient release rates of these materials. A manure nutrient equivalence or fertilizer substitution rate is given with both organic and chemical home garden recommendations. Manures and compost are too variable in content and rarely have the proper balance of nutrients to be used as the only source for all nutrients.
The management tips that appear below the lime and fertilizer lines contain general information on the placement, timing, or other modifications of the lime and fertilizer recommendations. They also contain specific information for some crops or management situations and warnings of common problems. This information is often just as important as the lime and fertilizer recommendations themselves. Be sure you read all the information on the report form.
Useful information for all crops
Banding of fertilizer or other amendments in the root zone ensures the most efficient use of these materials by the crop plants. It is especially critical if one or more nutrient levels is listed as “LOW.”
If you are not topdressing an existing crop, be sure to till or harrow in any compost, manure, lime (or sulfur), and phosphate amendments to ensure complete soil contact and better availability. These materials and nutrients do not readily move from the surface through the root zone when topdressed and will not move deeper than an inch or two during the growing season.
Because soils have a poor capacity to hold available nitrogen, a split application of nitrogen fertilizer is desirable for most crops, whether you use a chemical or organic nitrogen source. Plants need most of their seasonal nitrogen requirements during the period of rapid stem and foliar growth in early to mid-summer. Nitrogen applied just before this rapid growth stage is less likely to be lost from the root zone before the plant actually needs it. This is particularly important during years of heavy rainfall. Problems can also occur if nitrogen fertilizer is applied too late in the growing season. Specific recommendations for split application of nitrogen fertilizer will appear for those crops that will most benefit from it.
Important information that affects many home gardeners and organic growers is the modification of nitrogen recommendations based on organic matter level. In gardens, it is quite common for manures, compost, or other nutrient-rich organic matter sources to be added every year or two. The normal breakdown and release of nutrients from organic matter is more likely to supply a significant amount of nitrogen under these conditions. A soil with an organic matter level of 5 to 8 % should supply half or more of the seasonal nitrogen requirement for most garden crops. An application of about a quarter of the recommended nitrogen at planting time should be sufficient for the entire season in this case. This assumes the regular use of manure or compost. If peat moss, wood chips, or sawdust have been used, apply the quarter rate at planting time and the remainder of the full rate at early mid-season, regardless of the organic matter level.
Organic matter management
Active management of soil organic matter is essential, whether you use chemical or organic practices. Soil organic matter is very important in determining soil nutrient holding capacity, water holding capacity, structure, tilth, drainage, aeration, buffering capacity, and overall health. It should be monitored and actively managed, just as you would soil pH. Soil tillage of any kind will tend to speed the natural breakdown process of organic matter in soil. Soil organic matter should be replenished with yearly applications of animal manure, compost, cover crops, leaves, or other organic material. The establishment of a sod cover, as with hay land or turf, will tend to increase and maintain soil organic matter over time, even if no other sources of organic material are applied.
If organic matter is at an optimum level, only moderate quantities should be added each year. If organic matter is above optimum, none should be applied for a year or two to allow the level to decline through normal breakdown. Applying an excess of organic material can, in some cases, cause wild fluctuations in nitrogen availability. Temporary tie-up (immobilization) of available nitrogen can cause poor growth and greatly reduced yields. The release of too much available nitrogen can cause excessive height and foliar growth and delayed fruiting and ripening.
It is relatively difficult to build and maintain soil organic matter level in very sandy soils, since the normal breakdown rate of organic matter in these soils is very rapid. Certain sources of organic material provide a more lasting effect on soil organic matter than others. For sandy soils, organic materials that break down slowly, such as peat moss, finished compost, or leaves, are preferable to applying animal manure or other materials which break down more rapidly.
Warnings will appear for some specific crops if it is likely that the wrong management technique or nutrient source will adversely affect plant growth or yield.
For instance, late application of nitrogen fertilizers on tree crops may increase the likelihood of winter damage to new growth. pH and nutrient balance problems may occur from the over-application of wood ashes on home gardens or other crops. An above optimum pH level will limit the availability of some nutrients, especially micronutrients. Soil acidification may be needed in these cases. Specific warnings like these are given where problems commonly occur.
The laboratory results and the associated calculations can be the most confusing part of the report form. The numerical results are listed at the bottom of the report form as extra information, since they have already been interpreted for you in the Relative Nutrient Level section of the report form. Directly underneath each of the levels found or calculated there is an explicit listing of the optimum range for each of these values for the crop being grown. This can be used as a further aid to interpreting your test results. An explanation of each of the numerical terms follows:
Soil pH is the traditional measurement of the intensity of the acidity (or alkalinity) of your soil. A pH below 7.0 is acidic. A pH above 7.0 is alkaline. pH is measured in a soil/water paste made with distilled water. It is very useful as an index of relative acidity, but does not by itself predict lime requirement with great accuracy. Optimum pH level is 6.0 – 7.0 for home gardens, 5.5 – 6.5 for turf. The optimum soil pH for potatoes is 5.5 to 6.0. Acid-loving plants have an optimum pH level of 5.0 or lower.
Lime index is a pH measurement taken in a buffer solution that has been added to the soil to react with acidity. It is used to measure the total exchangeable or reserve acidity in the soil. It can be thought of as a simulated liming of the soil to measure its response to a lime application. The lime index, together with the current soil pH measured in water, is used to accurately calculate the quantity of soil acidity to be neutralized and the lime application necessary to raise your soil pH to the optimum level for the crop you plan to grow.
Pounds per acre extractable Phosphorus (P) is an index for phosphorus availability. It is not a direct measure of plant P uptake, but correlates well with the amount of phosphorus that plants can access from this soil over the next growing season. The per acre estimation assumes a 6 – 7 inch tillage layer or rooting zone. Most soils have about the same capacity to hold and supply phosphorus, so test levels are reported on a pounds per acre basis only. The optimum level for most vegetable and ornamental crops is from 20 to 40 pounds per acre (0.5 to 1 lb per 1000 sq. ft.) or the equivalent on a smaller area. Any phosphorus test level over 40 lb per acre is considered above optimum for these crops. Plants with a permanent root system (shrubs, trees, and turf grass) are much more efficient at accessing P in the soil. The optimum P test level for these crops is considerably lower. For example, established turf grass has an optimum P test level of 7 to 10 lb/A.
Pounds per acre exchangeable Potassium(K), Magnesium(Mg), and Calcium(Ca) are indices for the availability of these nutrients over the next growing season. As with the phosphorus level, the pounds per acre estimation assumes a 6 – 7 inch tillage layer or rooting zone. The available portion of these three nutrients is held by the soil and taken into plants as positively (+) charged particles called cations. The optimum level of these nutrients varies with the ability of the soil to hold cations. This will be explained in more detail next.
Cation Exchange Capacity (CEC) is an estimation of the soil’s ability to hold cations. It is a measure of the amount of active negative (-) charge in the soil. Since opposite charges attract, these (-) charged sites in the soil selectively hold the (+) charged cations. CEC varies according to soil texture, organic matter content, and pH. The (-) exchange sites hold most of the available potassium, magnesium, and calcium in the soil as well as exchangeable or reserve acidity (mostly aluminum).
The CEC that appears on the report form is not directly measured. Instead, it is estimated by converting the exchangeable Ca, K, Mg, and acidity levels found to equivalent amounts of (+) charge. All the (+) charges can then be added together. The sum of the (+) charges is assumed to equal the net (-) charge or CEC of the soil. Soil charges are expressed in terms of milliequivalents per 100 grams of soil (me/100 gm). In most soils, the net negative (-) charge or CEC will increase as the pH is increased. Because of this it is necessary to take into account the change in CEC after a recommended lime application. CEC is estimated at a projected pH, which varies depending on the crop to be grown. This projected pH or pH management level is explicitly stated for your crop in the first line of the Laboratory Results section. Because of this variation in nutrient holding capacity, a single soil can have two entirely different CEC estimates if recommendations are requested for two crops with different optimum pH levels.
By estimating the CEC, the optimum level of the three nutrient cations can be determined relative to the total capacity of the soil to hold them. In fact, for most crops the CEC is the basis for reporting and making recommendations for calcium, potassium, and magnesium. There is no explicit interpretation of relative level (low-medium-optimum) for CEC. In general, a CEC of 7 to 15 me/100 gm is a sufficient nutrient holding capacity for most crop production systems. A CEC value below 5 me/100 gm can become a limiting factor to plant growth and production.
Percent saturation is the portion of the estimated CEC that is occupied by the three exchangeable nutrient cations and exchangeable acidity, at their present levels. Optimum levels vary by crop, but for most crops grown in Maine, optimum nutrient levels to support maximum yield are in the following saturation ranges:
3 – 5% Potassium
10 – 20% Magnesium
60 – 80% Calcium
Percent saturation also provides information regarding nutrient imbalance and potential uptake competition. Since potassium, calcium, and magnesium can compete with each other for exchange sites in the soil and for uptake into plants, it is important that they not be drastically outside their optimum ranges. Plants will grow and produce equally well at a range of K, Mg, and Ca test levels, but uptake competition should be avoided if each is maintained somewhere within the ideal percentage ranges listed above.
Percent exchangeable acidity is reported to show the portion of the total nutrient holding capacity occupied by acidity under present conditions. Acidity is primarily composed of exchangeable aluminum, which is not an essential nutrient and can actually be toxic to sensitive plants under low-pH conditions. Acid-loving plants require a low pH (high acidity) soil and can tolerate relatively high levels of aluminum. Lime is recommended where necessary to reduce acidity to near zero. As the lime reacts in the soil, the acidity will be displaced and those exchange sites occupied by more useful nutrient cations: calcium and magnesium.
CEC adjustment — When a sample is taken after a recent lime application, there will still be a certain amount of unreacted lime in the soil. In these cases, the laboratory nutrient extraction procedure will dissolve some of this unreacted lime. The amounts of calcium and magnesium found will be partly from exchange sites and partly from dissolved lime. This will produce a false estimation of CEC. To correct for this situation, an additional test is run on all high pH samples to identify those calcium and magnesium levels which are inflated from dissolved lime. Milliequivalent levels of calcium and magnesium are corrected where necessary during the summation process for the purpose of estimating CEC. The reported lb/A values remain unchanged. In those cases where an adjustment has been made, this symbol will appear to the right of the CEC value: (A). This adjustment ensures that a reasonable estimation of CEC has been made, which will in turn give a more accurate assessment of the saturation levels and balance of the three nutrient cations and acidity.
Organic matter is the amount of decayed or humified organic material (crop residues, compost, manures, etc) in the soil. There are several possible methods that can be used to measure soil organic matter level. In the simple ignition method, the soil is heated to a very high temperature to burn off the organic matter. The other major method, more commonly referenced, is to chemically digest or oxidize the organic carbon in the soil. Both techniques are equally valid for monitoring organic matter content, but give different numerical results. The Maine Soil Testing Service measures organic matter by the ignition method, but converts this value to and reports in terms of the chemical oxidation method.
The ideal soil organic matter level, from the standpoint of nutrient cycling and fertility, is 5 – 8 %. If organic matter level falls below 2 – 3 %, the nutrient and water holding capacity of the soil becomes very limited and may not be sufficient to support normal plant growth during some growing seasons. A very high organic matter level (greater than 10 %) can cause wild fluctuations in the availability of some nutrients, especially nitrogen. In these cases, it is best to apply no organic matter for a year or two, to allow fresh organic material to stabilize as humus.
Sulfur is an essential plant nutrient, reported as parts per million (ppm) of plant-available sulfur. For plant nutrition purposes, sulfur is considered optimum or sufficient at a test level of 15 ppm or higher. If the sulfur test level is medium or low (less than 10 ppm), sulfur-containing fertilizers or amendments should be applied. Quite often, sulfur may be present in materials already recommended: manures, compost, Elemental sulfur or Aluminum sulfate acidifiers, Sul-Po-Mag (0-0-22-11), Potassium sulfate (0-0-50), Ammonium sulfate (21-0-0), Gypsum, or Epsom salt. After the application of soil acidifiers it is common for the sulfur test level to be well above optimum, which is not detrimental to plant growth or yield.
Micronutrients: Copper (Cu), Iron (Fe), Manganese (Mn), and Zinc (Zn) are required by all plants for proper growth and productivity, but only in minute amounts. They are only rarely limiting to plant growth or productivity in Maine soils. Zinc can occasionally be limiting to growth and yield in certain sensitive crops, such as corn. The optimum range for zinc availability is 1 – 2 ppm for most of these sensitive crops. Since copper, iron, and manganese are so rarely limiting, the reference test levels for these micronutrients are presented as the “normal range” of each in Maine soils. The availability of these micronutrients can often be managed simply by adjusting pH and/or organic matter levels in your soil. Supplemental information is included on micronutrient management with all soil reports and also on our website (anlab.umesci.maine.edu). Suggested micronutrient fertilizers and other amendments are also included in this information.
Lead Scan — All home/grounds soil samples are scanned for possible lead contamination. Lead is a naturally occurring trace element present in all soils at a normal background level of less than 50 parts per million (ppm). Lead “enrichment” or contamination of soils is a problem almost exclusively around older buildings or building sites. The usual source of this contamination is lead paint chips flaking, scraped, or sand blasted from these buildings over several decades. Lead paint was not banned until the 1970’s.
The lead scan is NOT a complete test for the presence of lead contamination. It is an initial screening for the presence of lead at a level higher than the normal background level. The lead scan report will indicate either a normal background level, a moderate contamination level, or a heavy contamination level. A normal background level would pose no health risk due to the lead content of the soil. A moderate to heavy contamination could, under the right circumstances, significantly add to the total daily intake of lead for those people working or playing in that area. Any vegetable garden, in which there is an indication of moderate to heavy lead contamination, will automatically be tested for total lead content. Any ornamental or lawn area with an indication of heavy contamination will also be tested for total lead content. A separate report with suggested guidelines and actions will be sent at a later date, usually within 2 to 4 weeks.
Lead is primarily a concern with growing children, who are much more sensitive to it than are adults. To be harmful, lead must be ingested by eating or breathing the dust. Plants do not typically accumulate dangerous quantities of lead internally. Surface contamination of edible parts from dust, rain spatter or direct soil contact (as with root crops) is usually the most significant source of plant contamination. Additional information on lead contamination is available through your UMaine Extension county office or through the lab website.
If you have paid in advance for the analysis of your sample(s), this will be indicated on the very bottom line of the report form for each sample. If our records indicate that full payment was not received, you will also receive an invoice with your report(s) indicating the amount still due.
Be sure that you have received credit for any payment you sent in with the sample(s). If there is an error in our records, please write, call, or email us so that we can correct our records of your account. Statements will be sent out monthly on any unpaid balances over two months old.
If you have a problem or question on the interpretation of your results or recommendations, please contact the nearest UMaine Extension county office. An Educator or crop specialist can help you with most general problems concerning soil testing.
Refer any problems of questionable results, additional analysis, incorrect crop codes, billing problems, etc. to the Maine Soil Testing Service lab. Soil samples are stored as long as space permits after they are initially processed in case it is necessary to run additional analysis. All results, recommendations, and customer information are permanently stored electronically for easy retrieval, reprinting, or modification.
Maine Soil Testing Service
University of Maine
Orono ME 04469-5722
207-581-2945 | 207-581-2934
Glossary of Terms
Amendment: any material added to the soil to enhance or increase nutrient content or availability. Lime, fertilizer, manure, compost, etc.
Ammonium-nitrogen: a form of mineral nitrogen commonly used in commercial fertilizers which is ultimately converted to nitrate-nitrogen by microbial action. (see Nitrogen section)
Available: the quantity of a nutrient element in the soil which is accessible for plant uptake at some point in the growing season.
Banding: the practice of placing fertilizer or other soil amendment in a strip below and to the side of the row when planting or in a circle around transplants.
Blend (fertilizer): the specific combination of nutrient materials used to produce a fertilizer of a guaranteed grade.
Calcitic lime: ground limestone containing less than 6% magnesium.
Calcium carbonate equivalence (CCE): rating of the acid-neutralizing value of a liming material, depending on the purity and chemical composition of the material.
Cation exchange capacity: measurement of a soil’s ability to hold cations against leaching. A measure of the soil’s potential nutrient holding capacity. (see Cation Exchange Capacity section)
Corrective fertilizing: applying nutrients in excess of the total needs of the crop being grown, for the purpose of raising the residual soil nutrient level after the crop has been removed.
Dolomitic lime: ground limestone containing about 10% or more magnesium.
Exchange (exchangeable): removing nutrient cations from exchange sites in the soil during measurement or plant uptake.
Exchange sites: locations on clay or organic matter particles with negative (-) charges which can hold nutrient cations. All exchange sites taken together make up the total negative charge or cation exchange capacity (also called the exchange complex). (see Cation Exchange Capacity section)
Exchangeable (reserve) acidity: the total quantity of acidity held by the soil which must be neutralized to raise the soil pH. It is comprised mostly of aluminum. At lower pH’s it occupies a significant portion of the exchange sites in the soil. (see Lime Index section)
Extraction (extractable): a general term for the removal of nutrients from the soil during measurement or plant uptake.
Grade (fertilizer): the guaranteed percent content by weight of a commercial fertilizer in terms of percent nitrogen, phosphate(P2O5), and potash(K2O). The same grade can be produced with entirely different sources of each nutrient.
Humification: the initial breakdown or decay of organic material in soil to form organic matter or humus.
Leaching: the removal of nutrients from the surface layer of soil by the actions of water percolation through the soil or by flooding with ground water.
Magnesium lime: ground limestone containing (by law) 6 % or more magnesium.
Major nutrient: any nutrient necessary for plant growth in relatively large amounts – nitrogen, phosphorus, potassium, calcium, magnesium, sulfur.
Micronutrient: any nutrient necessary for plant growth in relatively minute amounts – boron, copper, iron, manganese, molybdenum, zinc.
Nitrate-nitrogen: a form of nitrogen which is easily leached from soils. The primary form of nitrogen used by most plants. (see Nitrogen section)
Nutrient balance: the ideal condition of exchangeable calcium, potassium, and magnesium being present at the same relative level. (see Relative Soil Nutrient Level section and Percent Saturation section)
Nutrient imbalance: a situation where nutrient cations are present at greatly different relative levels, usually caused by an excess of one of them. (see Relative Soil Nutrient Level section and Percent Saturation section)
Organic matter: a mixed and variable component of the soil, composed primarily of plant residues, manures, and composts in various stages of decomposition. (see Nitrogen section and Organic matter section)
Phosphate (P2O5): the chemical representation of any and all phosphorus sources in commercial fertilizers.
Potash (K2O): the chemical representation of any and all potassium sources in commercial fertilizers.
Projected or target pH: the optimum pH level of the soil for the crop being grown, achieved after a recommended lime application has completely reacted. (see Cation Exchange Capacity section)
Relative nutrient level: classification of a particular nutrient or other soil component level as low, medium, optimum, or above optimum for a given soil and crop.
Split application: the practice of applying a total recommendation of lime or fertilizer over two or more separate applications spaced months or years apart, to gradually increase nutrient levels in the soil.
Starter fertilizer: typically a high phosphorus fertilizer applied at planting or transplanting to stimulate rapid root growth and early establishment of seedlings.
Topdressing: the even distribution of a soil amendment (lime, fertilizer, manure, etc.) on an established crop or sod without tilling it in.