| Most soils in Alabama must be fertilized for optimum
production. Unfertilized soils are naturally low in plant nutrients
because the parent materials from which they were formed were low
in phosphorus (P), and many were low or medium in potassium (K).
In addition, Alabama's relatively high temperatures plus rainfall
have caused release, leaching, and runoff of nutrients from fields,
especially where they have been croped continuously and the surface
has been allowed to erode. Likewise, the nitrogen (N) supplying
capacity of soils is dependent on the organic matter content which
is low in Alabama soils because of rapid decomposition under prevailing
environmental conditions. Therefore, unless these major nutrients
have been built up in soils by past fertilization and management
practices, soils will need fertilizer for sustainable production.
Most Alabama soils have been in continuous production for
more than 100 years. Some have been fertilized regularly throughout
that period. The addition of nutrients to soils and crops where
they are not needed and cannot be utilized is not only a waste
of resources but could also be environmentally unsound.
Nutrient needs were originally determined
by thousands of simple fertilizer experiments
conducted on farms throughout the State.
Prior to the establishment of the Auburn
University Soil Testing Laboratory in 1953,
general fertilizer recommendations were made
by Auburn University for different soil types.
These recommendations were based on these
cooperative experiments and other more complicated
experiments conducted on substations and
experiment fields located on the major soils
throughout the State.
This system is no longer adequate because
soils have been altered by past management.
Properly managed soils have become more productive
over the past 40 years as fertilizer use
has increased. Some nutrients may have been
depleted while others have been built up
in soils, depending on amounts supplied in
fertilizers and amounts removed in harvested
crops. General fertilizer recommendations
based on soil type are no longer practical
because past management practices now have
more influence on soil fertility than does
soil type. Soils separated only by a fence
may differ more in fertility than the original
unfertilized soils located in the different
regions of the State.
Soil tests have been developed to determine
the fertility level of individual soils.
This has required much field and laboratory
research at many locations over the years
to calibrate test results with response to
fertilizers in the field. Reliable soil tests
based on such research are now the only practical
basis for determining the needs of specific
crops on the many soil situations now existing
in Alabama.
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