E. J. Russell and E. H. Richards 505 



are extremely complex we have not attempted to follow them com- 

 pletely, and we are justified in this course by the field experiments 

 which we shall now describe. 



The relationship between the cornposition and the crop producing value 



of farmyard manure. 



Farmyard manure has to serve two functions in the soil : to supply 

 nitrogen in various forms, and also to supply organic matter which has 

 certain well-known physical eftects on the soil. It is not difficult to 

 estimate the nitrogen in some of its combinations, but it is difficult 

 to give any analytical figures except the total dry matter that will 

 show any relation to the physical effects. In order to discover how far 

 the analytical results were related to crop producing power our experi- 

 mental manure heaps were applied to the land at the conclusion of 

 each experiment, and the resulting crops were weighed. 



The experiments were only continued for one season : our previous 

 experience indicating that the later seasons bring out no new differences 

 between different samples of farmyard manure, and indeed only tend 

 to obliterate the old ones. 



The results obtained from dressings, of various samples of farmyard 

 manure are given in Table I. 



Table I. Relation between crop producing poiver and chemical 

 composition of samples of farmyard manure. 



1915. Potato Experiments, Rothamsted. 10 tons per acre of stored 

 farmyard manure applied. 



