INTRODUCTION 7 



the different substances from which plants derive their 

 nourishment" 3 



Soon after Liebig's first work appeared, the investi- 

 gations at Rothamsted by Sir J. B. Lawes were under- 

 taken. The most extensive systematic work in both 

 field experiments and laboratory investigations ever 

 conducted has been carried on by Lawes and Gilbert 

 at Rothamsted, Eng. Dr. Gilbert had previously been 

 a pupil of Liebig, and his becoming associated with 

 Sir J. B. Lawes marks the establishment of the second 

 experiment station. Many of the Rothamsted experi- 

 ments have been continued since 1844, and results of 

 the greatest value to agriculture have been obtained. 

 The investigations on the non-assimilation of atmos- 

 pheric nitrogen by crops, published in 1861, were ac- 

 cepted as conclusive evidence upon this much-vexed 

 question. Their work on manures, nitrification, the 

 nitrogen supply of crops, and the increase and decrease 

 of the nitrogen of the soil when different crops are pro- 

 duced, has had a most important bearing upon main- 

 taining the fertility of soils. 



" The general plan of the field experiments has been 

 to grow some of the most important crops of rotation, 

 each separately, for many years in succession on the 

 same land, without manure, with farmyard manure, 

 and with a great variety of chemical manures, the 

 same kind of manure being, as a rule, applied year 

 after year on'the same plot. Experiments with differ- 

 ent manures on the mixed herbage of permanent grass 



