1896.] PUBLIC DOCUMENT— No. 33. 113 



deservedly of late engaged the most careful attention of agri- 

 cultural investigators. 



The experiments in part described within a few subsequent 

 pages were planned in 1883, and have been continued to the 

 present time upon the same tield, with such modification as 

 circumstances advised. 



The investigations have been divided into three periods : — 



(a) Study of the existing soil resources of plant food, 

 1884 to 1889. 



(b) Study of the effect of excluding nitrogen plant food 

 from outside sources and of adding nitrogen plant food in 

 various available forms, 1889 to 1892. 



(c) Studying the effect of the cultivation of leguminous 

 crops on the resources of available nitrogen plant food in 

 the soil under treatment, 1892 to 1896. 



The systematic treatment of the field here under considera- 

 tion, as far as suitable modes of cultivation and of manur- 

 ing are concerned, was introduced during the season of 

 1883 to 1884. 



The subdivision of the entire area into eleven plats, " one- 

 tenth of an acre each," of a uniform size and shape, 132 

 feet long and 33 feet wide, with an unoccupied and un- 

 manurcd space of 5 feet in width between adjoining plats, 

 has been retained unaltered since 1884. A detailed state- 

 ment of the temporary aim and general management of the 

 experiments, as well as of the results obtained in that con- 

 nection from year to year, forms a prominent part of my 

 contemporary printed annual reports, to which I have to 

 refer for further details, 1884-95. The first four years of 

 the stated period 1884-89 were principally devoted to an 

 investigation into the general character and condition of 

 the soil under cultivation, as far as its natural and inherent 

 resources of available phosphoric acid, nitrogen and potash 

 were concerned. TJie soil 'proved to be in particular defi- 

 cient in potash. Different varieties of corn (maize) were 

 raised in succession to assist in the investigation. 



Since 1889 the main object of observation upon the same 

 field has been to study the influence of an entire exclusion 

 of any additional nitrogen-containing manurial substance 



