Interpreting Your Soil Test Results

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  • 7/24/2019 Interpreting Your Soil Test Results


    Interpreting Your Soil TestResults

    Interpreting Your Soil Test Results

    The primary goal of soil testing is to inform ecient and eective resource

    management. Soil testing is the most accurate way to determine lime and nutrient

    needs. Soil testing is also useful for identifying contaminated sites (e.g., elevated levels

    of lead.

    The results provided on your soil test report re!ect the properties of the sample you

    su"mitted and the testing procedures used "y the #niversity of $assachusetts Soil and

    %lant Tissue Testing &a"oratory. The analytical methods used "y the la"oratory were

    developed for climate and soil types common to 'ew ngland and the 'ortheastern

    #.S. It is important to recogni)e that the values o"tained when a soil sample is

    analy)ed are of little use as raw analytical data. In order to ma*e use of the values in

    predicting nutrient needs, the test must "e cali"rated "y conducting nutrient response

    research, under local conditions with representative soils ranging from de+cient to

    adeuate for each nutrient of concern. The optimum range (or typical range in some

    cases is provided in the column to the right of your results. These interpretations, as

    well as lime and fertili)er recommendations, are "ased on +eld and greenhouse trials

    conducted in $assachusetts and other 'ortheastern states. Recommendations provided

    with your soil test report are speci+c to the crop selection that you identi+ed on your

    soil sample su"mission form and are "ased on the analytical results for your sample.

    The purpose of this fact sheet is to provide a "rief e-planation of each of the values

    provided on your soil test report and how they are used to generate recommendations.


    Modifed Morgan Extractable Nutrients:

    The la" uses the $odi+ed $organ e-traction procedure, originally developed at the

    #niversity of onnecticut in the early /012s for use on 'ew ngland Soils. It is

    a universal e-traction procedure, meaning it is used to determine all ma3or nutrients

    and many of the micronutrients simultaneously. 'early all of the 'ew ngland State

    #niversities and ornell use the $organ e-traction procedure.

    Phosphorus (P) 45mong other important functions, phosphorus provides plants with a

    means of using the energy harnessed "y photosynthesis to drive its meta"olism. 5

    de+ciency of this nutrient can lead to impaired vegetative growth, wea* root systems,

    poor fruit and seed uality, and low yield6 however, e-cessive soil phosphorus levels

    are a concern due to the potential negative impact on surface water uality. $ost

    phosphorus losses occur with runo, "ut where soil levels are e-tremely high,

    su"surface losses can occur. %hosphorus enrichment is a leading source of water

    uality impairment of many la*es, streams, and rivers in 'ew ngland.
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    Soil phosphorus e-ists in a wide range of forms. Some phosphorus is present as part of

    soil organic matter and "ecomes availa"le to plants as the organic matter decomposes.

    $ost inorganic soil phosphorus is "ound tightly to the surface of soil minerals (e.g., iron

    and aluminum o-ides. 7arm, moist, well8aerated soils at a p9 level of a"out :.;

    optimi)e the release of "oth of these forms. %lants reuire fairly large uantities of

    phosphorus, "ut the levels of phosphorus availa"le to plant roots at any given time are

    usually uite low. .Soil tests attempt to assess the a"ility of soil to supply phosphorus

    from "ound forms during the growing season. 7hen a soil test indicates that

    phosphorus is low and fertili)er is needed, the rate recommended is intended to satisfy

    immediate crop needs and "egin to "uild soil phosphorus levels to the optimum range

    (i.e., "uild and maintain. %hosphorus recommendations are customarily e-pressed as


  • 7/24/2019 Interpreting Your Soil Test Results


    is reuired, dolomitic lime (rich in $g will "e recommended. If $g is low and lime is not

    reuired, psom salts (magnesium sulfate may "e recommended.

    Sulfur (S)4Sulfur is a component of several en)ymes that regulate photosynthesis and

    nitrogen +-ation. The vast ma3ority of sulfur in soil is stored in soil organic matter and

    is converted to availa"le mineral form "y the action of soil microorganisms. In 'ew

    ngland, atmospheric deposition resulting from com"ustion of fossil fuels has

    historically contri"uted signi+cant amounts of sulfur to soil each year6 however, with

    improved emissions control and the use of cleaner fuels, sulfur deposition has "een

    reduced. Still, sulfur de+ciencies are rare in 'ew ngland and an optimum range for

    $odi+ed $organ e-tracta"le sulfur has never "een identi+ed. The interpretation of

    e-tracta"le sulfur levels found on your report is "ased on what is typically found. 7hen

    sulfur levels are low, several sources of sulfur are availa"le to ensure adeuate plant

    nutrition includingA gypsum (calcium sulfate, potassium sulfate (2828;2 and sul8po8

    mag (2828or some crops, the amount of %

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    (assuming the sample su"mitted is representative of the area of concern. stimated

    total lead levels a"ove 122 ppm are a concern. In such cases, consult the separate

    insert on soil lead levels.

    Cation Exchange Caacit! and Soil "cidit!:

    Cation Exchange Capacit4ation e-change capacity ( is a measure of the soilDs

    a"ility to retain and supply nutrients, speci+cally the positively charged nutrient ions

    called cations. These include the cations calcium (a ollowing the fertili)er and lime recommendations provided with your report

    will typically result in "ase saturation values within normal ranges.

    Soil p! and Exchangeable Acidit 4 =ne of the most valua"le pieces of information you

    can get from soil testing is a measure of soil acidity. Soil p9 is an indicator of the soilDs

    acidity which is a primary factor controlling nutrient availa"ility, micro"ial processes,

    and plant growth. 5 p9 of G.2 is neutral, less than G.2 is acidic, and greater than G.2 is

    al*aline. $aintaining proper soil p9 is one of the most important aspects of soil fertility

    management. $ost 'ew ngland soils are naturally acidic and need to "e limed

    periodically to *eep the p9 in the range of :.2 to G.2 desired "y most crops and

    ornamental plants. 7hen the soil is acidic, the availa"ility of nitrogen, phosphorus, and

    potassium is reduced, and there are usually low amounts of calcium and magnesium in

    the soil. #nder acidic conditions, most micronutrients are more solu"le and are

    therefore more availa"le to plants. #nder very acidic conditions aluminum, iron, and

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    manganese may "e so solu"le they can reach to-ic levels. Soil acidity also in!uences

    soil micro"es. >or e-ample, when soil p9 is low ("elow :.2, "acterial activity is

    signi+cantly reduced. 5cidic soil conditions also reduce the eectiveness of some


    7hen soil p9 is maintained at the proper level, plant nutrient availa"ility is optimi)ed,

    solu"ility of to-ic elements is minimi)ed, and "ene+cial soil organisms are most active.

    7hile most plants grow "est in soil with a p9 "etween : and G, there are some nota"le

    acid8loving e-ceptions, including "lue"erry and rhododendron, which perform "est

    under soil conditions associated with a lower p9.

    Bue to the climate and geology of 'ew ngland, soils here tend to "e naturally acidic

    (C.;8;.;.The most eective way to manage soil acidity is to apply agricultural

    limestone. The uantity of lime reuired is determined "y the target p9 ("ased on

    crops to "e grown and the soils "uering capacity. ?uering capacity refers a soilDs

    tendency to resist change in p9. Soil p9 is a measure of active acidity, "ased on the

    concentration of hydrogen ions (9E in soil solution, and is an indicator of the current

    soil condition. 7hen lime is added to a soil, active acidity is neutrali)ed "y chemical

    reactions that remove hydrogen ions from the soil solution. 9owever, there are also

    acidic cations (9E and 5l1E adsor"ed on soil colloids (the which can "e released

    into the soil solution to replace those neutrali)ed "y the lime. This is called

    e-changea"le acidity. Soils such as clays or those high in organic matter have a high

    cation e-change capacity ( and a potential for large amounts of e-changea"le

    acidity. These soils are said to "e well "uered. To eectively raise the soil p9, "oth

    active and e-changea"le acidity must "e neutrali)ed. The la" determines "uering

    capacity and lime reuirement "y estimating the e-changea"le acidity. -changea"le

    acidity, which is reported in units of meF/22 g, is directly related to the uantity of

    lime reuired to increase the p9 from its current level to the target level determined "y

    the selected crop.

    =ccasionally soil p9 must "e lowered, "ecause either the plant reuires acid soil or the

    soil was previously over8limed. Incorporating elemental sulfur (S is the most eective

    way to lower soil p9. =nce applied, the sulfur o-idi


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