895 



The subiocts tresitod are: (1) The Kothaiusterl Experimental Station, 

 (2) the eirciimstaiices whicli (leteniiine the rise and fall of uitrogeuous 

 matter in the soil, (3) uitriticatioii, (4) iiitriticatioii and denitritication, 

 (5) nitrification of soil and niannres, (0) d)'ainaj;"e and well waters. A list 

 of Kothanisted papers referred to in the lectnres is given in an ai)pendix. 



Lecture I. — The liothamsfed Experimental Station (p[). 7-131). — This 

 gives a general a(X!onnt of the origin, history, i)lans, and resnlts of 

 experimental work at Rothamsted, and is devoted to practically the 

 same subjects as those covx'red by a paiHi)lilet issued l)y that station in 

 June, 1801, an abstract of which will be tVumd in l«]xperinuMit Station 

 Record, vol. iii, p. 73. In addition the endowment and managers of 

 the Lawes trust are given. 



Lecture IT. — The eireumstances ichich determine the rise and fall of 

 nitrogenous mutter in the soil (pp. 22-41). — "■ Ii^itrogen of soils exists in 

 three very different forms of combination, (1) as ammonia, (2) as nitrates, 

 and (3) as nitrogenous organic matter. The ammonia is generally insig'- 

 uiflcaut in amount. Although itself a jiroper food for plants, it is only 

 seldom that it has any importance from this point of view, owing to its 

 rapid conversion into nitric acid. The quantity of nitrates present in 

 the soil is usually far more considerable tlian that of ammonia, though 

 it is very rarely that 5 per cent of the total nitrogen of the soil exists 

 in this state. * * * The great bulk of the nitrogen contained in soil 

 occurs in combination with carbon and the elements of water, forming 

 the so-called humic compounds or nitrogenous organic matter of the 

 soil." 



The nitrogenous matter of soil is the residue of former animal and 

 vegetable life and there are probably very few sedimentary rocks which 

 do not contain an appreciable amount of nitrogen. Borings of calca- 

 reous clay (Oxford) from a depth of about 500 feet below the surface 

 showed 0.04 per cent of nitrogen. The examination of samples of Roth- 

 amsted subsoils, taken in many cases at as great a depth as 9 feet, 

 show that while there is a variation in different places of from 0.03 to 

 0.06 per cent of nitrogen, there is no indication that it diminishes' as we 

 descend after a certain distance from the surface has been reached. 

 "The nitrogen of this deep subsoil is to be regarded as in great 

 part of ancient origin, belonging in fact to the clay when originally 

 deposited. A sandy subsoil is usually poorer in nitrogen than one of 

 clay. The nitrogenous matter of our surface soils, with Avhich agricul- 

 ture is chiefly concerned, is undoubtedly in greatest part of niodern 

 origin, and the processes which bring about its accumulation and dimi- 

 nution are at the present day in progress under our own eyes and deserve 

 our most careful study." 



The production or accumulation of uitrogen in the surface soil is 

 illustrated by tabulated analyses of R')thamsted and Manitoba soil at 

 dei)ths varying in the first case from !) inches to 9 feet, and in the sec- 

 ond from 1 to 4 feet. "With undisturbed soils lying in natural prairie 



