Before the availability of artificial fertilizers in the mid-19th century, farms were traditionally organic, with recycling of animal waste, and perhaps with the application of lime on acid soils. Agricultural chemical analysis may have begun with Carl Wilhelm Scheele (1742-1786), the Swedish pharmacist who isolated citric acid from lemons and gooseberries and malic acid from apples. In France, Nicolas Theodore de Saussure (1767-1845) studied the mineral composition of plant ash, and in Britain, Sir Humphrey Davy

© 2002 CAB International. Methods in Agricultural Chemical Analysis: a Practical Handbook (N.T. Faithfull)

(1778-1829) analysed plants into 19 constituents, estimated the feeding value of 97 different grasses, and published his Elements of Agricultural Chemistry in 1813 (Faithfull, 1993).

The term 'Father of Agricultural Chemistry' is usually ascribed to Baron Justus von Liebig (1803-1873). In 1840, Liebig withdrew from the sphere of pure organic chemistry to apply his genius to the study of agricultural chemistry. He finally put the nail in the coffin for the humus theory, which claimed that plants mainly derived their carbon from humus in the soil rather than carbon dioxide. The role of nitrogen-fixing bacteria on the nodules of leguminous plants was only presented in 1886 and published in 1887, after Liebig's death. He therefore was under the misapprehension that most of the plant's nitrogen supply originated in ammonia from the air. He was aware, however, of the efficacy of legumes as nitrogen gatherers (Curtis, 1942). Another deficiency was the fact that he never took the acidity of the soil into account (Bradfield, 1942). Liebig assiduously carried out analyses of the mineral components of plant ash from the viewpoint that if the mineral elements removed from the soil by a particular plant species could be replaced or increased by application of a fertilizer compounded in the same proportions of mineral elements as found in the ash, then the yield would be enhanced. He considered the minerals to be in the form of solutions held in a state of physical absorption within the soil, the role of the cation exchange properties of clay and humus in the soil not yet being discovered. In this context, (Walters, 1989, p. 161), Albrecht quotes S.C. Hood who said, 'The oldest and most persistent of these errors may be referred to as the Liebig Complex. Over 100 years ago Justus von Liebig announced that plants needed from the soil no more than proper amounts of nitrogen, phosphorus and potash in water-soluble forms' (Liebig, 1840).

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