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Parts per million (ppm)
Results for the major and minor elements are reported in parts per million (ppm) on an elemental basis. An acre of mineral soil 6 to 7 inches deep weighs approximately 2 million pounds. Therefore, to convert parts per million readings to pounds per acre, multiply by 2.
Meq/100g (milliequivalents per 100 grams)
Soil cations, such as calcium, magnesium, potassium and hydrogen can be expressed in terms of their relative ability to displace other cations. The unit of measure meq/100g serves this purpose. For example, one milliequivalent of potassium is able to displace exactly one milliequivalent of magnesium. The cation exchange capacity of a soil, as well as the total amounts of individual cations, may be expressed by using these units.
Electrical conductivity measurements are often used to measure the amount of soluble salts in the soil. Conductivity is generally expressed in mmhos/cm. The conductivity increases with increasing soluble salts. The soil is considered saline when the conductivity reading of the saturation reaches 2 mmhos/cm.
Most soil test readings on the report are given a rating of very low (VL), low (L), medium (M), high (H), or very high (VH). The purpose of these readings is to provide a guideline for determining optimum nutrient levels for crop growth. Upon request, an unrated form can be obtained. Optimum levels may vary slightly from those shown on the Soil Analysis Report, however, the best value is dependent on many factors such as crop, yield potential and soil types.
Organic Matter and ENR (Estimated Nitrogen Release)
Percent organic matter is a measurement of the amount of plant and animal residue
in the soil. The color of the soil is usually closely related to its organic
matter content, with darker soils being higher in organic matter. The organic
matter serves as a reserve for many essential nutrients, especially nitrogen.
Bacterial activity releases some of this reserve nitrogen, making it available
to the plant. The ENR is an estimate of the amount of nitrogen that will be released
over the season. In addition to organic matter level, ENR may be influenced by
seasonal variations in weather conditions as well as physical soil conditions.
Three types of phosphorus tests may be reported. The P1 (weak Bray) test measures
phosphorus which is readily available to the plants. The optimum level will
vary with crop yield and soil conditions, but for most field crops, 20 to 30
ppm is adequate. Higher levels may be needed for especially high yields as
well as for certain vegetable crops. The P2 (strong Bray) test measures readily
available phosphorus plus a part of the active reserve phosphorus in soil.
A level of 40 to 60 ppm is desirable for good yields of most crops.
The bicarbonate P(sodium bicarbonate) test measures the amount of
readily available phosphorus in slightly basic (pH of 7.0 - 7.2) to highly
basic soils (pH 7.3 and greater). In basic soils the phosphorus exists mostly
as alkaline earth phosphates. The extraction by dilute sodium bicarbonate correlates
with what the crops can extract from these soils. The weak and strong Bray
extractions are acidic (low pH). These extracting solutions are neutralized
by the presence of free lime in higher pH soils, thus giving lower phosphorus
The relationship between P1 and P2 can help evaluate the phosphorus fixing ability
of the soil. A wide ratio (greater than 1 to 3) may be the result of high soil
pH, free calcium, high clay content or use of highly insoluble phosphate fertilizer.
A narrow ratio (less than 1 to 2) means either the soil does not have a fixing
ability for phosphorus or that a highly soluble source of phosphorus has been
This test measures available potassium. The optimum level will vary with crop,
yield, soil type, soil physical condition, and other soil related factors. Generally,
higher levels of potassium are needed in soils high in clay and organic matter;
lower levels in soils which are sandy and low in organic matter. Optimum levels
for light-colored, coarse textured soils may range from 100 to 150 ppm. Dark-colored,
heavy textured soils may require potassium levels from 150 to 250 ppm.
Magnesium and Calcium
The levels of calcium and magnesium found in the soil are affected primarily
by soil type, drainage, liming and cropping practices. These basic cations are
closely related to soil pH. As the soil pH increases, the levels of calcium and/or
magnesium usually increase. Calcium deficiencies are rare when the soil pH is
adequate. Magnesium deficiencies are more common. Adequate magnesium levels normally
range from 50 to 70 parts per million. The need for magnesium can be further
determined from its base saturation, which should be above 10 percent.
Sodium is considered as it relates to the physical condition of the soil. Adverse
physical and chemical conditions may develop in soil high in exchangeable sodium.
These conditions may prevent the growth of plants. Reclamation of these soils
involved the replacement of exchangeable sodium by calcium or magnesium and the
removal of sodium by leaching.
The soil pH measures active soil acidity or alkalinity. A pH of 6.9 or less is
acid. Soils with a pH of 7.0 are neutral, values higher than 7.0 are alkaline.
Under normal conditions the most desirable pH range for mineral soil is 6.0 to
7.0 and 5.0 to 5.5 for organic soil.
The buffer index is a value used for determining the amount of lime to apply
on acid soils with a pH of less than 6.6. The lower the buffer index, the higher
the lime requirement.
Cation Exchange Capacity (CEC)
Cation Exchange Capacity measures the soil's ability to hold nutrients such as
potassium, magnesium, and calcium, as well as the other positively charged ions
such as sodium and hydrogen. The CEC of a soil is dependent upon the amounts
and types of clay minerals and organic matter present. The common measurement
for CEC is milliequivalents per 100 grams (meq/100g) of soil. On most soils it
will vary from 2 to 35 meq/100g depending upon the soil type. Soils with high
CEC will generally have higher levels of clay and organic matter. For example,
one would expect soil with a silty, clay loam texture to have a considerably
higher CEC than a sandy loam soil. Although high CEC soils can hold more nutrients,
good soil management is required if these soils are to be more productive.
Percent Base Saturation
Percent base saturation refers to the proportion of the CEC occupied by a given
cation (an ion with a positive charge such as calcium, magnesium or potassium)
or combination of cations referred to as bases. The percentage saturation for
each of the cations will usually be within the following ranges for optimum performance.
- Potassium: 1 to 5
- Magnesium: 10 to 40
- Calcium: 60 to 80
The soil test measures nitrate-nitrogen (NO3-N) which is water soluble and readily
available for the plant. When considering nitrogen levels needed for optimum
crop performance, this test will indicate the level of nitrate-nitrogen present.
Depth tests determining NO3-N will give more detailed information for making
nitrogen recommendations. It is important that other soil factors including organic
matter content are taken into consideration when interpreting the nitrate-nitrogen
soil test and predicting crop response. This test is not suited for high CEC
soil, or high rainfall areas.
The soil test measures sulfate sulfur (SO4-S) which is readily available and
preferred for plant uptake. Optimum levels for sulfur depend on organic matter
content, soil texture, drainage, and desired yield goal. Whenever the following
conditions exist, the need for sulfur will normally be increasingly important
for optimum crop performance.
- Well-drained, low CEC soils
- Soils low in organic matter
- Low soil pH (below 6.0)
- Use of high-analysis, low-sulfur fertilizers
The 0.1 NHCl extraction is used to extract zinc. A test level of 3 to
6 ppm is normally adequate. If the DTPA extraction is requested, a level of 1.8
to 2.5 ppm should be adequate under normal conditions. Factors taken into consideration
when interpreting the zinc test include available soil phosphorus, pH, crop and
A test range of 20 to 30 ppm of extractable manganese is usually adequate when
the 0.1 NHCl extraction is performed. A test range of 14 to 22 ppm is
adequate when using the DTPA extraction. Soil pH is especially important in interpreting
manganese test levels. In addition, soil organic matter, crop and yield goal
must also be considered. Since manganese quickly reverts to insoluble (unavailable)
forms shortly after application, row or band treatments and foliar applications
are the recommended methods for applying manganese.
A level of 20 to 30 ppm of extractable iron is usually adequate for either the
0.1 N†HCl or the DTPA extraction. Soil pH is a very important factor in
interpreting the iron soil test. In addition, crops vary a great deal in sensitivity
to iron deficiency. Foliar applications provide the best results when correcting
A level of 1 to 1.8 ppm of copper should be sufficient for both extraction methods.
The soil pH, organic matter level, high rates of nitrogen, and the crop to be
grown are important factors that should be considered when interpreting copper
Readily-available boron is extracted from the soil with hot water. Adequate levels
range from 1 to 1.5 ppm. Factors to be taken into consideration when interpreting
the boron test should include pH, organic matter and texture, as well as the
crop to be grown.
Excess Lime Rate
A visual rating of free lime is reported. Soils high in free lime tie up major
and minor elements making them unavailable to the plant. An application of elemental
sulfur or acid forming fertilizer can be beneficial in keeping phosphorus and
micronutrients in soluble form. Excess lime will have an effect on the degradation
of some herbicides.
If the level of salinity is less than 1.0 mmhos/cm the effect is negligible.
Readings greater than 1.0 mmhos/cm may affect salt-sensitive plants. A level
greater than 2.0 mmhos/cm may require planting salt tolerant plants. An excessive
concentration of various salts may develop naturally or be the result of poor
irrigation water, excessive fertilization, or contamination from various chemicals
or industrial wastes. One effect of high soil salt concentration is to produce
water stress in a crop which may cause the plant to wilt or even die.
Additional requested analyses such as chloride or aluminum will be shown in this
This section of the report is used by the agronomist to address problems when
specific test results indicate a need for special interpretation. Specific answers
or special attention to a certain aspect of the soil test requested by the client
will also appear in this section.
All samples are filed by report number. When contacting A†&†L†concerning
a certain report, be sure to refer to this number.
An account number has been assigned to each A†&†L†client.
The use of this number will speed up sample processing and location of samples
within the laboratory system.
The identification number assigned by the client to each individual sample is
reported here. Because of limited space, sample numbers must be limited to 4
The identification number which was assigned by the laboratory to each individual
soil sample is shown here.
Agronomist reviewing report.
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