2 The Value of Soil Analyses to the Farmer. 



stock the addition of another 25 lb., such as would be contained 

 in 2 cwt. of nitrate of soda, may increase the crop by 20 per 

 cent, or more. 



Facts of this kind led the chemists to attempt to draw a 

 distinction between the plant food in the soil that was available, 

 i.e., could be taken up by the plant, and the dormant stock 

 which needed to undergo some chemical change to reach the 

 form that could be utilised by the plant. Moreover, they began 

 to attack the soil with certain very weak acids in the hope of 

 extracting thereby only the available but not the total plant 

 food which was present in the soil. The method thus intro- 

 duced, though it did give additional information about the 

 capacity of the soil to bear particular crops, by no means 

 removed all the difficulties ; a large excess even of available 

 plant food was revealed in most soils, and the standard that 

 had to be attained to ensure fertility was found to vary with 

 both the crop and the character of the soil ; e.g. a sandy soil 

 with 0*01 per cent, of so-called available phosphoi-ic acid might 

 grow turnips perfectly well, whereas a clay soil with the same 

 percentage would need some superphosphate or other phosphatic 

 manure to ensure a reasonable yield. 



Many attempts were made to obtain a precise distinction 

 between the available and dormant plant food, but without any 

 general measure of success, so much so that there has arisen in 

 America a school of soil investigators who deny that the amount 

 of plant food in the soil as revealed by analysis influences its 

 fertility. The argument of Whitney and Cameron is that the 

 water in the soil from which the plant draws its nutrition can 

 only attain a certain degree of concentration in phosphoric acid 

 and potash by contact with the soil minerals containing these 

 elements, just as water can only take up a certain percentage of 

 salt. Moreover, such a saturated soil solution must possess 

 practically the same composition for all soils because they all 

 contain the same minerals. For example, water in contact 

 with a soil containing phosphate of lime will attain the same 

 concentration in phosphoric acid whether there is one or ten 

 parts per thousand of phosphate of lime in the soil. It would 

 follow as a consequence from this view not only that a chemical 

 analysis of the soil is a matter of no importance towards forming 

 an opinion as to its fertility, but that the plant itself is equally 

 indifferent to the amount of plant food it has at command, 

 its growth being determined by some other factors. 



We need not here consider the various points of controversy 

 that have arisen over these views of the American Bureau of 

 Soils ; the point worthy of notice is that they remind us, with 

 perhaps exaggerated emphasis, of the other functions which 

 the soil has to fulfil towards the plant. The soil not only 



