Firstly, soil
fertility is a complex concept when referring to the potential of a soil to
supply nutrients in the normal amounts, forms and proportions required for
optimum plant growth. Describing soil fertility in total is beyond the scope of
this content. Soil properties that affect the necessary nutrient supply to plants
include organic matter, soil texture, cation exchange capacity as well as soil
pH.
Organic
Matter
The
organic matter of the soil affects both the chemical and physical properties of
a soil even though it makes up only 1 to 5 percentage of the soil mass. In
addition to holding available plant nutrients in an exchangeable form, nutrient
is released by organic matter when it decomposes. Crop residues, manure, and
other organic materials contain significant amounts of nitrogen, phosphorus, sulfur
and boron and serves as a reservoir for these nutrients, which become available
as soil microorganisms convert the organic nutrients into inorganic, plant
available forms. Soil organic matter influences soil physical characteristics
such as soil erosion, soil temperature, water holding capacity and drainage.
Additions of organic materials to the soil will increase the amount of water held
available for crops in sandy soils and improve drainage in heavier textured
soils by its influence on pore space. Adding organic matter to soils as manure
or green manure crops before planting is more beneficial than surface
applications with no incorporation after plant is establishment.
Soil
texture
The soil
texture describes the feel and nature of the soil, its coarseness or fineness.
More specifically, it is the relative proportion of sand, silt and clay that
make up the mineral portion of a soil. All textures of soil are found in various
parts of Wisconsin. Plants will grow in most soil types as long as they have
enough, but not too much, water and nutrients in such soil. Additions of
organic matter will help minimize soil limitations due to texture but will not
entirely remove severe problems.
Cation
Exchange Capicity
One of the
most important and necessary reservoirs of plant nutrients in the soil is the
exchangeable nutrients held on cation exchange sites. Most of the potassium,
ammonium, calcium and magnesium used by plants emerge from this exchange sites.
Each soil has a finite capacity to hold positively charged nutrients, the cation
exchange capacity. Silt and clay soils can hold several times more positively
charged nutrients than sandy soils. However, even sands have adequate exchange
capacity to hold all of the nutrients needed by plants in an available form.
The
soil pH
The establishing
and maintenance of proper soil pH by the use of limestone contributes an
important role in productivity due to the fact that it influences the soil pH
on nutrient availability and other chemical and biological processes affecting
plant growth. The pH of the soil affects the availability of plant nutrients.
Optimum availability of plant essential nutrients is ensured when mineral soil
pH is maintained between 6.0 and 6.5. In some circumstances nutrient
deficiencies or toxicities can be avoided by adjusting the soil pH to the
proper volume.
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