RELATION OF FERTILISERS TO SOIL FERTILITY. 13 



on this point is not conclusive, but it is fairly certain that the increases^ 

 when such have been found, are insufficient to account for the great increase 

 in fertility noted by Ptussell and Hutchinson (three or four times the crop 

 in the case of heat, and 20 to 50 per cent, in the case of volatile antiseptics). 



S. U. Pickering* shows a slight increase in the total water-soluble material, 

 both of heated and of treated soils, but the nature of the mineral matter 

 extracted is not stated. 



G. S. Frapsf has found that previous ignition increases the amount of 

 phosphoric acid, which can be dissolved from several naturally occurring 

 phosphates. Wavellite, in particular, yields ten times as much phosphoric 

 acid, soluble in -|-nitric acid, after as before ignition. 



It is to be remembered, however, that in this case there is no question of 

 the presence of agricere, and further, that, in our soils, at all events, these 

 minerals are not likely to be present in any quantity. 



C. B. LipmanJ finds in the case of soils the opposite effect to that noted 

 by Fraps in the case of phosphatic minerals. He finds that the effect of 

 igniting soil is to reduce the amount of phosphoric acid extracted by nitric 

 acid. This agrees with the observations of J. Konig and others that 

 phosphoric acid is fixed by colloids in the soil forming insoluble calcium 

 phosphate, so that the combination is rendered more complete by the action 

 of heat. 



H. I. Jensen|| has also investigated this point. He treated several soils 

 of varying known degrees of fertility with different soil-solvents before and 

 after ignition -e.g., strong hydrochloric acid (sp. gr. 1 4 1), citric acid (1 per 

 cent.) and nitric acid (?). 



The results are very irregular and vary in different directions, being 

 frequently identical, but they point to the conclusion that in the case of 

 heated soil at all events the increased fertility is not due to the greater 

 solubility of the recognised plant-foods. Any considerable differences occur 

 only in cases where the quantities of plant-food are extremely small and are 

 probably due to experimental errors. 



C. B. Lipman^[ has carried out experiments in which previously sterilised 

 soil was infected with filtered suspensions, so as to remove the protozoa. He 

 finds no difference in the results when such filtered liquids are used and 

 when unfiltered suspensions containing protozoa are employed, and is "unable 

 to confirm the claims of Russell and Hutchinson as to the influence of 

 protozoa in modifying the amount of work done by decay bacteria." 



Another view of the action of heat upon soils has been more recently advanced 

 by O. Schreiner and E. C. Lathrop** and E. C. Lathropff. These authors find 

 that heating the soil results in an increase in the water soluble constituents 



* Jonrn. Agric. Sci., vol. 3, p. 32. 



t Journ. lid. Eny. Chemistry, vol. 3, p. 335. 



Journ. Ind. Eny. Ghent., vol. 4, p. 603. 



Lar.d. Vcrsuch. ftat., 1911, vol. 75, pp. 377-441. 



|| Prcc. Hoy. A'oc., N.S.W., vol. 45, p. ]f>9. 



IF Xew Jersey A^ric. Expt. Station, Bull. 248. 



* Journ. Am. Chcm. Soc., vol. 34, p. 1242. 



tt Jbid., p. 1-260. 



