12 SOIL CONDITIONS AND PLANT GROWTH 



sity of ammoniacal manures were deleted from the third and later 

 editions. " If the soil be suitable, if it contains a sufficient quantity of 

 alkalis, phosphates, and sulphates, nothing will be wanting. The 

 plants will derive their ammonia from the atmosphere as they do car- 

 bonic acid," he writes in the Farmers Magazine. Ash analysis led 

 him to consider the turnip as one of the plants " which contain the least 

 amount of phosphates and therefore require the smallest quantity for 

 their development ". These and other practical deductions were seized 

 upon and shown to be erroneous by Lawes (160-162) who had for some 

 years been conducting vegetation experiments. Lawes does not discuss 

 the theory as such, but tests the deductions Liebig himself draws and 

 finds them wrong. Further trouble was in store for Liebig ; his patent 

 manure when tried in practice had failed. This was unfortunate, and 

 the impression in England at any rate, was, in Philip Pusey's words : 

 " The mineral theory, too hastily adopted by Liebig, namely, that 

 crops rise and fall in direct proportion to the quantity of mineral sub- 

 stances present in the soil, or to the addition or abstraction of these 

 substances which are added in the manure, has received its death-blow 

 from the experiments of Mr. Lawes ". 



And yet the failure of the patent manure was not entirely the fault 

 of the theory, but only affords further proof of the numerous pitfalls 

 of the subject. The manure was sound in that it contained potassium 

 compounds and phosphates (it ought of course to have contained nitrogen 

 compounds), but it was unfortunately rendered insoluble by fusion with 

 lime and calcium phosphate so that it should not too readily wash out 

 in the drainage water. Not till Way had shown in 1850 that soil pre- 

 cipitates soluble salts of ammonium, potassium and phosphates was the 

 futility of the fusion process discovered, and Liebig saw the error he 

 had made (173^). 



Meanwhile he continued to defend his position in the controversy 

 with Lawes and Gilbert. It is not possible in this short sketch to go 

 into details, but by 1855 the following points were settled by the 

 experiments made at Rothamsted to test the various points raised : 



(1) Crops require phosphates and salts of the alkalis, but the com- 

 position of the ash does not afford reliable information as to the 

 amounts of each constituent needed, e.g. turnips require large amounts 

 of phosphates, although only little is present in their ash. 



(2) Non-leguminous crops require a supply of some nitrogenous 

 compounds, nitrates and ammonium salts being almost equally good. 

 Without an adequate supply no increases of growth are obtained, even 

 when ash constituents are added. The amount of ammonia obtainable 

 from the atmosphere is insufficient for the needs of crops. Leguminous 

 crops behaved abnormally. 



