INCREASE OF CROPS BY USE OF FERTILIZERS 19 



Some of the results of phosphatic manuring at Rothamsted 

 are summarized in Tables 2 and 3, which show the amount 

 of grain and straw yielded in three successive periods of 20 

 years each, under different treatments. 



During the many years in which barley was continuously 

 grown, none of the methods employed quite maintained the 

 yield, but the farmyard manure nearly achieved that object. 

 Complete chemical fertilizers have clearly failed somewhat in 

 this respect, but nothing like as strikingly as unbalanced 

 fertilizers lacking some important ingredient. It will further 

 be noticed that the most serious omission is nitrogen, and the 

 least important omission is potash, but this relationship 

 largely depends upon the characteristics of the soils; it is only 

 on light soils that potash is essential. With reference to the 

 straw, the use of farmyard manure has enabled the soil to 

 do more than maintain its position. Again, it will be seen 

 that nitrogen is more essential than phosphates, and phos- 

 phates more essential than potash. Barley does not seem to 

 permit of the replacement of farmyard manure by artificials 

 quite so readily as wheat does. 



The question as to whether phosphates have a specific 

 effect on transpiration in crops has been specially inquired 

 into by Leather in India. Many of the soils that he experi- 

 mented upon were markedly deficient in phosphates, and 

 responded to phosphatic manures, hence arose the question 

 whether the increased economy of water was due to the 

 specific effect of phosphates, or merely due to supplying a 

 soil with the particular element of plant food most needed. 

 He therefore employed a soil which apparently did not 

 require phosphatic fertilizers, as judged from the crops 

 produced, and in this case he found that the best plants and 

 the lowest transpiration ratios were obtained from the use 

 of purely nitrogenous fertilizers. He thus demonstrated 

 that the effect of superphosphate in the previous experiments 

 has been entirely due to the deficiency in this soil of readily 

 available phosphates, and not to any specific action on 

 transpiration by phosphates themselves. 



Leaf Development with Potassium. All the potassium 



