Fertilizer

Fertilizer are compounds given to plants to make them grow. Fertilizers can be naturally occurring compounds such as peat or mineral deposits, or manufactured through natural processes (such as composting) or chemical processes (such as the Haber process).

They typically provide the three major plant nutrients (nitrogen, phosphorus, potassium: N-P-K), the secondary plant nutrients (calcium, sulfur, magnesium), and sometimes trace elements (or micronutrients) with a role in plant nutrition: boron, chlorine, manganese, iron, zinc, copper, and molybdenum.

Both organic and inorganic fertilizers were called “manures” derived from the French expression for manualtillage, but this term is now mostly restricted to organic manure.

Though nitrogen is plentiful in the earth’s atmosphere, relatively few plants engage in nitrogen fixation (conversion of atmospheric nitrogen to a biologically useful form). Most plants thus require nitrogen compounds to be present in the soil in which they grow. While manure, cinder and ironmaking slag have been used to improve crops for centuries, the use of fertilizers is arguably one of the great innovations of the Agricultural Revolution of the 19th Century.

In the 1730s, Viscount Charles Townshend (1674-1738) first studied the improving effects of the four-crop rotation system that he had observed in use in Flanders.

The influential works of chemist Justus von Liebig (1803-1883) first denounced the vitalist theory of humus, arguing first the importance of ammonia, and later the importance of inorganic minerals.

Sir John Bennet Lawes (1814-1900) was experimenting with crops and manures at his farm at Harpenden and was able to produce a practical superphosphate in 1842 from the phosphates in rock and coprolites. Encouraged, he employed Sir Joseph Henry Gilbert, who had studied under Liebig at the University of Giessen, as director of research. To this day, the Rothamsted research station that they founded still investigates the impact of inorganic and organic fertilizers on crop yields.

10-20