2 RESULTS OF EXPERIMENTS AT ROTHAMSTED, 



for many years in succession on the same land, without any nitrogenous 

 manure ; or when grown in alternation one with another, also without 

 nitrogenous manure; that is to say, under conditions in which the soil 

 is to a great extent exhausted of accumulations of nitrogen due to 

 recent supplies by manure, and when, therefore, the plants have to rely 

 largely on what may be called the natural resources of the soil, and on 

 those of the atmosphere. - 



I shall next show the effects of artificial supplies of nitrogen, on 

 the growth of the different descriptions of plant, on the amount of 

 nitrogen they assimilate, and on the amount and character of their 

 products. 



Lastly, I shall adduce evidence of quite other kinds, as to the 

 sources of the nitrogen, more especially of the Leguminosce ; a question 

 which has been the subject of experimental enquiry, and at times of 

 active 'controversy, for about half a century; which has in recent 

 years assumed a somewhat new aspect ; but which cannot even yet be 

 said to be conclusively settled. 



YIELD OF NITROGEN PER ACRE PER ANNUM IN DIFFERENT CROPS, 

 WITHOUT NITROGENOUS MANURE. 



Table I. (p. 3), shows the yield of nitrogen per acre per annum, 

 with mineral, but without any nitrogenous manure in Wheat and 

 in Barley as Gramineous crops, in Turnips as representatives of the 

 Crucifera, in Sugar-Beet and Mangel-Wurzel of the Chenopodiaeea, 

 and in Beans and Clover as Leguminous crops, when each is grown for 

 many years in succession on the same land. It also shows, the amounts 

 of nitrogen yielded per acre, when Turnips, Barley, a Leguminous 

 crop, and Wheat, are grown in an actual course of rotation, also with 

 mineral, but without nitrogenous manure. 



Incidentally it is to be noticed that, in the case of each of the 

 crops Wheat, Barley, and Beans thus grown year after year on the 

 same land for many years in succession without nitrogenous manure, 

 there was a reduction in the yield of nitrogen per acre per annum, over 

 the second period compared with the first ; that is, as the accumulations 

 within the soil became reduced. 



Disregarding this tendency to reduced yield, it is seen that, over 

 the same period of 24 years, with full mineral but without nitrogenous 

 manure, the wheat yielded an average of 22-1 Ibs., and the barley 22 - 4 

 Ibs. of nitrogen per acre per annum ; the two allied crops, therefore, 

 yielding almost identical amounts, in their above-ground produce, 

 without nitrogenous manure, on soil very poor in available nitrogen, so 

 far as accumulations due to recent applications of nitrogenous manure 

 are concerned. 



Turning now to the yield of nitrogen in the root-crops, Turnips, 

 Sugar-Beet, and Mangel-Wurzel it may be mentioned that, prior to 

 the period referred to in the Table, Turnips had been grown for a 

 number of years, and had yielded 42 Ibs. of nitrogen per acre per 



