12 CHEMICAL FERTILIZERS 



In Table I it may be seen that, contrary to anything one 

 might have reasonably expected, farmyard manure has not 

 exhibited that striking superiority over artificial manures 

 that general farm experience would have suggested. At 

 Rothamsted the rainfall is not, perhaps, quite the lowest in 

 the British Isles, but it is a long way below the average, and 

 one would expect that so much farmyard manure, applied 

 for so many years, would have enabled the soil to regulate 

 the water supply in such a manner as to give the organic 

 manure an advantage over chemical fertilizers. As a matter 

 of fact, chemical fertilizers have beaten farmyard manure 

 over a stretch of so many years as to rule out altogether any 

 temporary or accidental influence. This important fact, 

 that nitrogen can be applied for so many years without any 

 exhaustion of the soil, has enabled Great Britain, during the 

 war, to increase her wheat yields by applications of sulphate 

 of ammonia. Had her government not been aware of 

 Rothamsted and its results, which had been copied and 

 confirmed under numerous and varied local conditions, 

 it would have been impracticable to have proceeded with the 

 vigorous wheat production that has taken place during the 

 war. Many wonderful things have been done during the 

 war, but probably there is nothing that can beat the achieve- 

 ment of a country that had previously failed to produce 

 one-fifth of its breadstufTs, increasing its yields in so short 

 a time under the stress of war, that it was able to bring the 

 production of breadstufTs up to more than three-quarters of 

 its requirements (see p. 180). 



Root Growth with Phosphorus. Of the oxides of 

 phosphorus it is only phosphorus pentoxide that is concerned 

 with any of the fertilizers. Phosphorus pentoxide by hydra- 

 tion gives meta-, pyro- or ortho-phosphoric acid accord- 

 ing to the amount of water that is taken up. In a soil, 

 the phosphoric acid exists in combination with calcium, 

 iron or organic matter. In some fertilizers pyro-phosphoric 

 acid may occur, as, for example, in super-phosphates that have 

 been overheated during the process of drying. 



Applications of phosphatic manures do not produce 



