THE FERTILITY OF THE SOIL 7 



driven this theory of plant nutrition home to all ; a science 

 of agricultural chemistry was founded, and such questions 

 as the function of the soil with regard to the plant could 

 be studied with prospect of success. By this time also 

 methods of analysis had been so far improved, that some 

 quantitative idea could be obtained as to the amount of 

 the various constituents present in soil and plant, and 

 naturally enough the first theory of soil fertility to be 

 framed required that fertility should be increased by 

 the addition of materials which were taken from it by 

 the crop. As the supply of air, from which the plant 

 derives its carbonaceous substance, is unlimited, the 

 extent of growth would seem to depend upon the supply 

 available of the other constituents which have to be 

 provided by the soil. 



It was DAUBENY, Professor of Botany and Rural 

 Economy in this University, and the real founder of 

 a science of agriculture in this country, who first pointed 

 out the enormous difference between the amount of 

 plant food in the soil and that taken out by the crop. 

 In a paper published in the Philosophical Transactions 

 in 1845, being the Bakerian Lecture for that year, 

 DAUBENY described a long series of experiments that he 

 had carried out in the Botanic Garden, where he culti- 

 vated various plants, growing some continuously on the 

 same plot, and others in rotation. Afterwards he com- 

 pared the amount of plant food removed by the crops 

 with that remaining in the soil. The results DAUBENY 

 obtained may be illustrated by the diagrams which show 

 the amounts of nitrogen, phosphoric acid, and potash in 

 some of our Rothamsted soils, compared with the amounts 

 of the same materials removed by the crops they pro- 

 duced. Roughly speaking, we may say that any normal 



