MISCELLANEOUS EXPERIMENTS 121 



phates, it is, however, by no means usual to make use of arti- 

 ficial manures supplying potash. It will thus sometimes 

 happen that a turnip crop is limited in its development by a 

 deficient supply of potash in the soil. 



The points now mentioned go far to explain the diversity of 

 results obtained in the use of ammonia salts. The ammonia 

 can only give a full return when the soil, or the manures em- 

 ployed, furnish (i) a sufficient supply of ash constituents to 

 the crop, and (2) an insufficient supply of nitrogen ; and when 

 these conditions are fulfilled, there is also required (3) the ex- 

 ternal conditions of light, heat, moisture, and tilth in the soil 

 necessary to produce a crop corresponding to the supply of plant 

 food. A failure in any one of these conditions will effectually 

 prevent a profitable return from the ammonia salts applied. 



As our present object is to ascertain what return may be 

 expected from sulphate of ammonia when used under conditions 

 reasonably favourable to its success, we will discard all groups 

 of experiments in which it produced no increase in the crop of 

 roots, and confine our attention to those in which some benefit 

 was obtained. In some of the groups admitted to use there are 

 individual farms giving no return from sulphate of ammonia, 

 these have not been struck out, as errors of experiment may 

 clearly occur both in the direction of deficiency and excess. 

 The experiments have next been divided into four classes : 

 (i) Experiments made without dung, but with phosphates and 

 potash salts ; (2) Experiments made without dung, with phos- 

 phates only ; (3) Experiments made with dung, and phosphates 

 and potash ; (4) Experiments made with dung, and phosphates 

 only. In calculating the average return from sulphate of am- 

 monia in each class, a value has been given to the results in 

 each group of experiments corresponding to the number of 

 farms on which the experiment was made. (p. 122). 



A large majority of the experiments were made in Scotland. 

 Those belonging to the Edinburgh centre were conducted by 

 Dr. Aitken, and will be found described in the Transactions of 

 the Highland Society. Those belonging to the Glasgow centre 

 were conducted by Professor \Yright, and are taken from his 

 Annual Reports. The Newcastle experiments were conducted 



