pH measures active soil acidity or
alkalinity. A pH of 7.0 is neutral. Values lower than 7.0 are
acid; values higher are alkaline. Usually the most desirable
pH range for mineral soils is 6.0 to 7.0 and for organic soils
5.0 to 5.5. The soil pH is the
value that should be maintained in the pH range most desirable
for the crop to be grown.
is an index value used for determining the amount of lime to
apply on acid soils to bring the pH to the desired pH for the
crop to be grown. The lower the buffer pH reading
the higher the lime requirement.
phosphorus test measures that
phosphorus that should be available to the plant. The optimum
level will vary with crop, yield and soil
conditions, but for most field crops a medium to optimum
rating is adequate. For soils with pH above 7.3 the sodium
bicarbonate test will determine
the available P.
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 on soils high
in clay and organic matter versus soils, which are sandy and
low in organic matter. Optimum levels for light-colored,
may range from 90 to 125 ppm (180 to 250 lbs/ac). On
dark-colored heavy-textured soils
levels ranging from 125 to 200 ppm (250 to 400 lbs/ac) may be
Primarily soil type, drainage,
liming and cropping practices affect the levels of calcium
found in the soil. Calcium is
closely related to soil pH.
Calcium deficiencies are rare
when soil pH is adequate. The
level for calcium will vary with soil
type, but optimum
ranges are normally in the 65% to 75% cation saturation range.
same factors, which affect calcium levels in the soil,
also influence magnesium
levels except magnesium deficiencies are more common. Adequate
range from 30 to 70 ppm (60 to 140 lbs/ac). The cation
saturation for magnesium should
be 10 to 15%.
measures sulfate-sulfur. This is a readily available form
preferred by most
plants. Soil test
levels should be maintained in the optimum range. It's
other soil factors, including
organic matter content, soil
texture and drainage be taken
into consideration when interpreting sulfur soil
test and predicting crop
readily soluble boron is extracted from the soil.
Boron will most likely be deficient in
sandy soils, low in organic matter with adequate rainfall. Soil
pH, organic matter level
and texture should be considered in interpreting the boron test,
as well as the crop to be
is most likely to be deficient on low organic matter sandy
soils, or organic soils. The crop to be grown, soil
texture, and organic matter should be considered when
interpreting copper tests. A rating of medium to optimum
should be maintained.
pH is a very important factor in interpreting iron tests. In
addition, crops vary a great deal in sensitivity to iron
deficiency. Normally a medium level would be adequate for most
soils. If iron is needed it would be best applied foliar.
pH is especially
important in interpreting manganese test
levels. In addition, soil organic
matter, crop and yield levels must be considered. Manganese
will work best if applied
foliar or banded in the soil.
factors, which should be considered in interpreting the zinc test,
include available phosphorus, pH, and crop and yield level.
For crops that have a good response to zinc, the soil
test level should be
is not an essential plant nutrient but is usually considered
in light of its effect on the physical condition of the soil.
Soils high in exchangeable sodium may cause adverse physical
and chemical conditions to develop in the soil.
These conditions may prevent the growth of plants. Reclamation
of these soils involves the replacement of the exchangeable
sodium by calcium and the removal by leaching.
concentration of various salts may develop in soils. This may
be a natural occurrence or it may result from irrigation,
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 to
where plants may wilt or even die. The effect of salinity is
negligible if the reading is less
than 1.0 mmhos/cm. Readings greater than 1.0 mmhos/cm may
affect salt sensitive plants and readings greater than 2.0
mmhos/cm may require the planting of salt tolerant plants.
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. During the growing season, a part of this reserve
nitrogen is made available to the plant through bacterial
activity. The ENR is an estimate of the amount of nitrogen
(lbs/acre) that will be released over the season. In addition
to organic matter level, this figure may be influenced by
seasonal variation in weather conditions as well as soil
Nitrate nitrogen is a measure of the nitrogen available to the
plant in nitrate form. In high rainfall areas, sandy soil
types and areas with warm winters, this measurement may be of
limited value except at planting or side dress time. In the
areas with lower rainfall, the nitrate test
may be very beneficial.
Exchange Capacity (CEC)
Cation exchange capacity measures the soil's
ability to hold nutrients such as calcium, magnesium, and
potassium, as well as 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 expression for CEC is in
terms of milliequivalents per 100 grams (meq/100g) of soil.
The CEC of soil can range from
less than 5 to 35 meq/100g for agricultural type soils. 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, it doesn't
necessarily mean that they
are more productive. Much depends on good soil
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). The percentage
saturation for each of the cations will usually be within the
40 to 80 percent
Magnesium: 10 to 40 percent
Potassium: 1 to 5 percent
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