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.