1 8 SOIL CONDITIONS AND PLANT GROWTH 



earlier by Boussingault, but they have the advantage that they 

 are still going on, having been continued year after year on the 

 same ground without alteration, except in occasional details, 

 since 1852. The mass of data now accumulated is consider- 

 able and it is being treated by modern statistical methods. 

 Certain conclusions are so obvious, however, that they can 

 be drawn on mere inspection of the data. By 1855 the fol- 

 lowing points were definitely settled (i66r) : 



(i) Crops require phosphates and salts of the alkalis, but 

 the composition of the ash does not afford reliable information 

 as to the amounts of each constituent needed, e.g. turnips re- 

 quire large amounts of phosphates, although only little is 

 present in their ash. Some of the results are : 



Composition of ash, per cent. 

 (1860 crop) 



K . 44-8 



P 2 5 ... 7-9 



Yield of turnips, tons per acre (1843)- 

 Unmanured . . . 4-5 

 Superphosphate . . . 12-8 

 ,, +potassic salts irg 



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

 genous 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. 



(3) Soil fertility may be maintained for some years at 

 least by means of artificial manures. 



(4) The beneficial effect of fallowing lies in the increase 

 brought about in the available nitrogen compounds in the 

 soil. 



Although many of Liebig's statements were shown to be 

 wrong, the main outline of his theory as first enunciated 

 stands. It is no detraction that de Saussure had earlier 

 published a somewhat similar, but less definite view of 

 nutrition : Liebig had brought matters to a head and made 

 men look at their cherished, but unexamined, convictions. 

 The effect of the stimulus he gave can hardly be over- 



