CHAPTER 1 



INTRODUCTION 



A rational system of agriculture must be based on an 



exact acquaintance with the means of nutrition of 



vegetables, and with the influence of soils and action 



of manure upon them. 



LlEBIG (1840) 



A. Historical 



The fact that calcined plants yield an ash containing inorganic 

 salts has been known since antiquity, and the beneficial effect on 

 crops of adding this ash to soil was recognized in early agricultural 

 practice (see opposite). Nevertheless, the origin and significance of 

 the mineral elements in plants for long remained a matter of 

 controversy, and, as recently as the nineteenth century, it was still 

 being argued with some conviction that salts are created de novo 

 within them as a by-product of growth. 



The classical experiment of Van Helmont (1577-1644), reported 

 by his son in Ortus Medicinae (1684) was the first quantitative 

 investigation of plant nutrition of which there is any record. He 

 planted a willow {Salix sp.) cutting, weighing 5 lb, in 200 lb of dry 

 earth, and watered it with rain-water over a period of 5 years. At 

 the end, the plant weighed 169 lb 3 oz, and the earth had lost about 

 2 oz in dry weight. The experiment successfully disproved Aristotle's 

 view that plants absorb their food in an elaborated form from the 

 soil (humus theory), but Van Helmont concluded, perhaps under- 

 standably in the existing state of knowledge, that 164 lb of plant 

 material had been produced from water alone. He did not enlarge 

 on the significance of the small decrease in dry weight of the soil, 

 which was presumably due to removal of inorganic substances. 

 Woodward (1699) pointed out that plants can survive with their 

 roots immersed in water, but growth is better in river water than in 

 rain-water, and best in a watery extract of soil (Table 1). On the 



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