dates, and to the same depths, with a view to comp;ini 

 tive results. The results already obtained, especially so 

 far as the nitrogen as nitric acid is concerned, are of 

 much interest ; and, as has been said, the further com- 

 parative investigation of these adjoining Leguminous 

 and Gramineous crop soils arid subsoils, promises, per- 

 haps, more fruitful results, than that of any of the other 

 Itothamsted experimental soils. 



Samples of soil were taken from the wheat-fallow 

 plots at 5 places to the depth of 3 times 9, or 27 inches, 

 in 1881 ; from 4 places to the depth of 12 times 9 inches, 

 or 108 inches, in 1883 ; and from 3 places, also to the 

 depth of 108 inches, or 9 feet, in 1885. The results of 

 the determinations of nitrogen by soda-lime in the 

 surface soils, and those of nitrogen as nitric acid in both 

 surface and subsoils, have been given and discussed, in 

 more or less detail, in Nos. 62, 64, 67, 77, and 81 in 

 the list. 



VII. EXPERIMENTS ON ROTATION, IN AGDELL FII.I.K 



1. The Field Results. 



It will be observed that, in the case of each of the 

 field experiments hitherto considered, the plan has been 

 to grow the same crop year after year on the same land, 

 without manure, and by different descriptions of manure. 

 In those now to be described, various crops are grown 

 in an actual and typical course of rotation, namely, the 

 so-called four-course rotation, of turnips, barley, Legu- 

 minous crop or fallow, and wheat. The experiments 

 were commenced in 1848, and are still in progress, so 

 that the crop of the present year, 1891, is the 44th, and 

 the fourth of the eleventh course of 4 years. 



One-third of the land has been unmanured from the 

 commencement, one-third has received mineral manure 

 only, and one-third a mixture of both mineral and nitro- 

 genous manure; the manures being applied once in 

 4 years only, that is for the turnips commencing each 

 course. From half of each of the 3 plots, the turnip-crops 



c 2 



