CHAPTER V 



THE FUNCTION AND USE OF PHOSPHATIC 

 FERTILISERS 



Ripening Effect of Phosphoric Acid — Most manifest in wet 

 Seasons — Effect of Phosphoric Acid in stimulating the 

 Formation of Roots and adventitious Shoots — Association of 

 Phosphoric Acid with the Intake of Nitrogen by the Plant — 

 Solvents to determine the relative Availability of Phosphatic 

 Fertilisers — Relative Value of Phosphatic Fertilisers deter- 

 mined by the Soil — Soils appropriate to Superphosphate — 

 Fate of Superphosphate applied to the Soil — Soils appropriate 

 to Basic Slag — Neutral Phosphatic Manures for light Soils — 

 Comparison of Bone Meal with other Phosphatic Fertilisers. 



Before considering the question of the relative fertilis- 

 ing value of the different phosphatic manures and their 

 application in practice, it will be necessary to get some 

 idea of the function of phosphoric acid in the nutrition 

 of the plant. 



Just as nitrogen delays maturity by promoting 

 growth, phosphoric acid has an opposite effect ; it is in 

 some way closely bound up with grain formation, being 

 always found in greater proportions in the reproductive 

 parts of the plant than elsewhere. This ripening action 

 is very clearly seen in the Rothamsted experiments on 

 barley ; the plots without phosphoric acid being as a 

 rule about a week behind those which receive this 

 fertiliser. 



This effect is brought out in the diagrams, Fig. 3, 



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