202 EXPERIMENTAL STATIONS. 



depends on the manner in which these have been met. They 

 are of two kinds, — those which by the exercise of skill, accuracy 

 and watchful care on the part of the experimenter may be 

 avoided or overcome, and those which lie beyond the control 

 of the most skilful and experienced. Chief among the latter are 

 diversity of soil, inequality of climate, and uncertainty of weather. 



The diversity of soil is a matter which usually does not 

 receive the attention which its importance demands, and it too 

 often happens that experimenters engaged in observing the 

 specific action of manures attribute to the manures themselves 

 effects which are due in great measure to the peculiar character 

 of the soils on which they are tried. The varieties of soil 

 which are often met with in a field of even a few acres are such 

 as to materially affect the operation of manures, and to occasion 

 differences in the crop which would not have occurred had the 

 soil been everywhere uniform. Even where a field is uniform and 

 well suited in that respect for an experimental station, the differ- 

 ence between its soil and that of other parts of the covmtry, even 

 in the neighbourhood, may be so great that the specific action of 

 certain manures applied to it may be very different from that 

 applied elsewhere. This is a circumstance wliich should warn 

 experimenters in drawing inferences from the results of their 

 experiments not to be too dogmatic, and to mistake for a general 

 law that which may, after all, have a very limited application. 

 It is not uncommon to hear a special form of manure lauded by 

 one experimenter as the one best suited for a certain crop, and 

 stigmatised by another as being comparatively useless. Some 

 express the opinion that sulphuric acid in any form is prejudicial, 

 and others that it is the ingredient in a superphosphate which is 

 most efficacious. Some declare that phosphates of mineral origin 

 are of small value compared with that derived from bones, and 

 care is taken by manufacturers, who sell bone phosphates only, 

 to let it be known that their manure is of purely animal 

 origin. Others assert that to attribute to animal phosphates 

 an efficacy superior to that of mineral phosphates is an entire 

 mistake. It was long accepted as a fact that mineral phos- 

 phates, unless dissolved by acid, were unable to be assimilated 

 by plants ; and yet experiments are produced to show that crops 

 are able to thrive on them in the undissolved state as well as in 

 the other. 



Conflicting opinions such as these are not necessarily due to 

 inaccurate observation or carelessness on the part of the experi- 

 menter, but more frequently to the inevitable contingencies 

 affecting all field experiments, and first among these is the various 

 nature of the soils in which the experiments have been tried. To 

 meet that difficulty as far as possible, it would be necessary to per- 

 form the same experiments on a variety of soils, and to investigate 



