interpreting your soil test results

7/24/2019 Interpreting Your Soil Test Results

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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.

SOIL TEST RESULTS

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.
https://soiltest.umass.edu/sites/soiltest.umass.edu/files/fact-sheets/pdf/SPTTL_2%20Interpreting%20Your%20Soil%20Test%20Results.pdfhttps://soiltest.umass.edu/sites/soiltest.umass.edu/files/fact-sheets/pdf/SPTTL_2%20Interpreting%20Your%20Soil%20Test%20Results.pdf


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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

%


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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

her"icides.

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)es to sulfuric acid. 5pplying ; to /2

l"s. of sulfur per /222 s. ft. will lower the p9 of most 'ew ngland soils "y

appro-imately half a unit. (#se the lower rate for very sandy soils. 'o more than /;

l"s. of sulfur per /222 s. ft. should "e applied at any one time. Retest the soil after C

to : months to determine if more sulfur is needed.

"dditional Otional Tests:

The la" oers several additional optional tests for routine analysis. 7hile each of these

tests can provide useful information under certain conditions, results are not directly

used to ma*e fertili)er or lime recommendations.

"rganic Matter 4Soil organic matter (S=$ is composed of materials containing car"on.

These materials include plant and animal remains (including "acteria and fungi in

various stages of decomposition, root and micro"ial e-udates and humus. 9umus is the

end8product of decay and is resistant to further decomposition. 'ative S=$ content of


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most cultivated or developed areas of 'ew ngland is almost always less than H and

typically in the < to C range. Several factors control the amount of S=$ a soil may

have, including soil te-ture and drainage. 7ell8drained, coarse te-tured soils tend to

naturally have lower levels of S=$. This is due, in part, to the rapid micro"ial

decomposition rates favored "y these soil conditions. In fact, it is dicult to maintain

high levels of S=$ in these soils without drastic, and sometime unsustaina"le,

measures. Bespite the low S=$ content of many 'ew ngland soils, it is an important

component of soil for nutrient supply, water holding capacity, cation e-change

capacity, and soil structure.

S=$ supplies nutrients through the process of minerali)ation, which is the

decomposition of organic compounds "y micro"ial action into car"on dio-ide and

mineral constituents. Soil micro"es are most active in warm soils (over G2J> that are

moist, "ut well aerated, with a p9 "etween : and G. $inerali)ation of nutrients will

proceed rapidly under these conditions. Three of the macronutrients are made availa"le

to plants "y minerali)ationA nitrogen (', phosphorus (%, and sulfur (S. S=$ has a

direct in!uence on water holding capacity due to its a"ility to a"sor" large amounts of

water, and indirectly "y improving soil structure, which creates more pore space for

water storage. Soil structure is enhanced "y S=$ "ecause in the process of

decomposition stic*y compounds are produced "y microorganisms. The cation

e-change capacity of soils is controlled "y the clay content and the S=$ content with

"oth materials supplying negatively charged sites for adsorption of cations. In most

'ew ngland soils, the humus portion of S=$ accounts for the vast ma3ority of the

cation e-change capacity.

The optimum range for S=$ for soil health varies across soil types. Kenerally, lower

levels of S=$ are sucient, and practical to achieve, in coarse te-tured, sandy soils as

compared to +ner soils with more clay content. >or e-ample, or this reason, soil nitrogen testing is not generally useful for predicting

fertili)er need in our humid environment. 'itrogen recommendations are "ased on crop

need with the assumption that very little availa"le ' remains in the soil after the

growing season. 5d3ustments should "e made "ased on soil organic matter content and

where soils were recently amended with manure or compost or where legumes are

grown in the rotation.

'itrate ('=18' analysis is oered as an additional optional test for routine analysis6

however, these results are not directly used to ma*e fertili)er recommendations. In

general, a soil '=18' concentration of 12 ppm or higher during the active growing

season is sucient for most plants. Interpretation of soil '=18' levels "elow 12 ppm is


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somewhat ne"ulous "ecause soil nitrogen is so dynamic. 7hen the concentration of soil

'=18' is less than 12 ppm, additional fertili)er may or may not "e needed.

#nder certain speci+c conditions soil '=1testing can "e useful for predicting fertili)er

needs. The %re8sidedress Soil 'itrate Test (%S'T has "een shown to successfully

predict sidedress fertili)er ' needs for a few crops (e.g., corn, pump*in, peppers,

ca""age, "ut the %S'T reuires stricter sampling (depth and timing and handling than

a standard soil fertility sample. ontact the la"oratory or visit the we"site for more

information on this test.

Soluble Salts4Solu"le salts, present in many commercial (and some natural fertili)ers

and deicing products used on sidewal*s and roads, can cause severe water stress and

nutritional im"alances in plants. Kenerally, seedlings are more sensitive than

esta"lished plants to elevated solu"le salts levels, and great variation e-ists "etween

plant species. $ost soils tested "y the #$ass la"oratory have values "etween 2.2H and

2.;2dSFm (mmhoFcm with the middle of the range typical of most fertile mineral soils.

7hen values are greater than 2.:2 sensitive plants (such as onions, etc. may suer

salt damage. The level of solu"le salts can change rapidly in the soil due to leaching, so

the eects of time and growing conditions are important considerations when

evaluating the signi+cance of the solu"le salts level. -cessive levels can often "e

corrected "y leaching with li"eral amounts (


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&a"oratory $anager6 Solomon @ariu*i, &a"oratory %rogram oordinator. Revised Muly

interpreting your soil test results

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