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For centuries, farmers have realized the need to maintain soil fertility to sustain or improve crop yields.The history of the production and use of inorganic fertilizer can be traced back to the nineteenth century when Justus von Liebig established the theoretical foundations of agricultural science and when John Bennett Lawes began producing fertilizers containing phosphorus (Smil, 1997).By accident or by trial and error, it was found that applications of various organic wastes or naturally occurring mineral substances, such as manure, compost, fish remains, ashes, saltpeter, and other materials, would sometimes increase crop yields or apparently restore the fertility of the land.The German scientist Liebig recognized the value of elements derived from the soil in plant nutrition and correctly deduced the necessity of replacing those elements in the soil to maintain soil fertility.While carbon, hydrogen, and oxygen, which collectively make up 90%-95% of the dry matter of all plants, are provided by the atmosphere, other essential nutrients are derived from the soil.These nutrients are classified as primary nutrients (nitrogen, phosphorus, and potassium) and secondary nutrients (calcium, magnesium, and sulfur).The use of fertilizer to replenish these nutrients results in many benefits to man and the environment, including: o Increased agricultural outputs (mainly food and fiber).In 1840 Liebig published a recommendation that pulverized animal bones be treated with sulfuric acid to make the phosphate more readily available to plants.Plants also need micronutrients (boron, chlorine, copper, iron, manganese, molybdenum, and zinc) in much smaller amounts.As the science of chemistry progressed and more and more chemical elements were discovered, the relative importance of various elements for plant growth and yield was identified.Nutrients taken up by crops must be replenished to maintain soil fertility and productivity and prevent land degradation.o Reserving lands marginally suitable for agriculture for other uses.o Increased water-holding capacity.

For centuries, farmers have realized the need to
maintain soil fertility to sustain or improve crop
yields. By accident or by trial and error, it was found
that applications of various organic wastes or naturally occurring mineral substances, such as manure,
compost, fish remains, ashes, saltpeter, and other
materials, would sometimes increase crop yields or
apparently restore the fertility of the land.
The history of the production and use of
inorganic fertilizer can be traced back to the nineteenth century when Justus von Liebig established
the theoretical foundations of agricultural science
and when John Bennett Lawes began producing
fertilizers containing phosphorus (Smil, 1997). As
the science of chemistry progressed and more and
more chemical elements were discovered, the
relative importance of various elements for plant
growth and yield was identified. The German
scientist Liebig recognized the value of elements
derived from the soil in plant nutrition and correctly
deduced the necessity of replacing those elements in
the soil to maintain soil fertility. Liebig is usually
credited with initiating the fertilizer industry. In 1840
Liebig published a recommendation that pulverized
animal bones be treated with sulfuric acid to make
the phosphate more readily available to plants. This
practice was accepted, and production of fertilizers
by chemical processing began in the 1840s.
Fertilizers provide plants with nutrients needed
for growth and development. Plants grow and
reproduce by utilizing nutrients, water, and carbon
dioxide from the air, and energy from the sun. While
carbon, hydrogen, and oxygen, which collectively
make up 90%–95% of the dry matter of all plants,
are provided by the atmosphere, other essential
nutrients are derived from the soil. These nutrients
are classified as primary nutrients (nitrogen, phosphorus, and potassium) and secondary nutrients
(calcium, magnesium, and sulfur). Plants also need
micronutrients (boron, chlorine, copper, iron, manganese, molybdenum, and zinc) in much smaller
amounts.
Nutrients taken up by crops must be replenished to maintain soil fertility and productivity and
prevent land degradation. The use of fertilizer to
replenish these nutrients results in many benefits to
man and the environment, including:
• Increased agricultural outputs (mainly food and
fiber).
• Increased water-holding capacity.
• Biological nitrogen fixation.
• Improved soil erosion control.
• Less extensive land use.
• Reserving lands marginally suitable for agriculture
for other uses.
Commercial fertilizers usually contain at least
one of the primary plant nutrients in a form that is
assimilable or “available” to plants. This includes
compounds that are water soluble or soluble in
special solutions that are used to estimate availability
to plants such as citric acid, neutral ammonium
citrate, or alkaline ammonium citrate. With nitrogen
fertilizers, slow release may be very desirable from
an environmental and efficiency standpoint.
Fertilizer products are customarily designated
by a series of numbers to express the grade of the
fertilizer product. Each of the numbers indicates the
amount of a nutrient contained in the fertilizer
product. This number includes only the amount of
nutrient present in a form that is available for plant
nutrition. The content of each nutrient is the guaranteed minimum rather than actual amount, which is
usually slightly higher. Three numbers are usually
used when expressing the grade of a fertilizer
product. These numbers always refer in order to the
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content of the primary nutrients: nitrogen, phosphorus, and potassium. If any other nutrient is present,
an additional number is given, followed by the
chemical symbol of the nutrient it represents. Most
countries indicate the content of phosphorus and
potassium in oxide forms, P2O5 and K2O. Therefore,
a fertilizer product with a grade of 12-6-22-2MgO is
guaranteed by the manufacturer to contain a minimum of 12% N, 6% P2O5, 22% K2O, and 2% MgO.
Some common fertilizers and common grades are
given in the following table.