CHAPTER IV. 



Influence of the varying quality of farm-yard manure on the results of experi- 

 ments in which it is one of the substances employed. Influence of the previous 

 treatment of the land. Influence of one substance in counteracting the bene- 

 ficial action of another. Influence of the time and manner of the application 

 of a manure, and of the period at which a root-crop is lifted. Influence of 

 the physical condition of a substance in its state of chemical combination, and 

 its tendency to decompose in a given soil. Influence of different varieties of 

 seed. Influence of seasons on the results of field experiments. When experi- 

 ments are to be rejected. Value of contradictory and of positive and negative 

 results. Is it desirable that experiments in practical and scientific agriculture 

 should be extensively made ] 



1. Influence of the varying quality of farm-yard manure on 

 the results of comparative experiments, in ivhich it is one of the 

 substances employed. 



NOTHING is better known than the varying quality of farm- 

 yard manure. Not only does it vary in fertilising value on 

 different farms, but upon the same farm also, and in some degree 

 in the same dung-heap ; so that we cannot expect from equal 

 weights of it at all times the same amount of effect in causing 

 crops to grow even on the same land. Supposing the nature 

 of the soil, therefore, to introduce no cause of diversity of the 

 kind adverted to in the preceding sections, this varying quality 

 of the farm-yard manure must influence in a greater or less de- 

 gree the results of every experiment in which it is made to play 

 a part, and must make the results of it open to suspicion. 

 Experience proves the correctness of this inference. Thus 



1. Mr Dockar, at Findon, some of whose experiments I have 

 already quoted, applied 20 loads of farm-yard manure to his 

 experimental turnip-field in 1843, and obtained from two mea- 

 sured eighths of an acre at the rate of 



