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2.2 Chemical Characteristics
Nutrient availability
Not all soil nutrients are available to plants. Some are so strongly held to clay or organic matter
particles that plants can not take them up. Others are in chemical forms that some organisms
cannot process.
Soil pH is often the chief factor in determining nutrient availability. The optimal pH for all soil
nutrient availability is between 6.5 and 7.5, in which condition most soil nutrients will be available
for crop uptake. Below pH 6.5 or above pH 7.5, certain elements will become less available, even if
they are present in the soil. Soil fertilizers need to be applied to some soils to compensate for lower
availability of a nutrient due to pH.
Deficiencies
Plants will not perform as well when some
nutrients are deficient, but it is not always
easy to tell from a plant’s appearance what
the underlying deficiency is; a soil test can
help confirm or rule out some possibilities. For
example, phosphorus deficiency is common
and occurs for two reasons: phosphorus
occurs at low concentrations naturally in soils
and phosphorus that is in soil or that is
added to soil is or becomes unavailable to
plants. Plants may exhibit the same or similar
symptoms of deficiency for lack of more
than one nutrient. For this reason, further
testing may be needed to exactly ascertain a
deficiency or combination of deficiencies.
Zinc deficiency in corn
Iron deficiency in sugarcane
Phosphorus deficiency in corn
Manganese deficiency in rose