8 SEASONAL NITRIFICATION AS INFLUENCED BY CROPS, ETC. 



area for the purpose of finding out, if possible, the best methods of 

 handling the prairie lands there so that profitable crop returns might 

 be realized. At all of these stations a large number of rotations have 

 been established, and other plats have been set aside for experiments 

 with various methods of cultivation without regard to crop rotations. 



In the spring of 1907 the writer was put in charge of the substation 

 at Belief ourche, S. Dak., where experiments in dry-land agriculture 

 were inaugurated. The station site was on virgin prairie lands, so 

 nothing was done that year beyond breaking up and preparing land 

 for use in 1908. In the spring of that year an elaborate series of 

 rotation systems was established, and a large number of other plats 

 were set aside for use in the studies of soil-moisture conservation by 

 different methods of cultivation, the success of the methods being 

 measured finally by the crop yields, though moisture determinations 

 were made during the entire season. 



The work to be described was done on some of the plats used for 

 the purpose of trying out different cultural methods, it being thought 

 that different crops and different tillage methods would influence 

 the nutritive properties of the soil solution. Owing to the press of 

 field duties and to the inconvenient location of the station as regards 

 supplies, it was found necessary to limit the laboratory work to a 

 study of the natural activity of nitrification in the soil as measured by 

 determinations of nitrates, nitrites, and ammonia in three plats receiv- 

 ing different treatments and bearing different crops. 



The literature on nitrifying organisms and on nitrification is very 

 voluminous, and while the author does not by any means claim to 

 have read it all, it is believed that most references which have any 

 direct bearing on the present subject matter have been cited. In no 

 case was there found reported work on nitrification in the field as 

 influenced by crops and tillage that had been carried on continu- 

 ously throughout the crop season. The few references found which 

 might have a bearing were generally reports on work carried on in 

 humid regions or in the laboratory, the conclusions of which could 

 hardly be extended to the semiarid regions. Much of the literature, 

 however, was helpful in formulating suggestions explaining the 

 phenomena found. 



DESCRIPTION OF THE SOIL IN WHICH THE EXPERIMENTS WERE 



CONDUCTED. 



The soil of the station and of the surrounding country is known as 

 "gumbo" and is a heavy, black or gray, clay loam to a depth of 2 to 

 3 feet, and below this depth heavy clay usually occurs, extending to 

 6 feet or deeper, overlying the partially disintegrated cretaceous shale 

 which is the geological formation of the whole surrounding country. 



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