MANURING 247 



drops of hydrochloric acid are poured on to a handful of soil, 

 there is a foaming or effervescence, that is a sign of the presence 

 of calcium or magnesium carbonate. If no foaming or effer- 

 vescence takes place it is evident that lime is not present, at 

 least in the form of carbonate. 



The tests employed by analytical chemists in analysing 

 soils are, of course, more complicated and more exhaustive. 

 The soil is generally ignited to determine by loss the amount of 

 humus and combined water and part is also treated in solution 

 with various acids to detect the presence and the proportions 

 of nitrogen, phosphorus, potassium, magnesium and calcium, 

 etc., and to indicate what deficiencies should be supplied. A 

 deficiency of any of these chemical elements always manifests 

 itself in poor and backward growth and in liability to disease. 

 The benefits of manuring are founded on the axiom that no 

 great abundance of the general elements of plant food can com- 

 pensate for a deficiency in one remaining important element. 



Of recent years there has been quite a change of opinion 

 and practice in more advanced circles interested in agricultural 

 chemistry. While at one time it was generally accepted that 

 the requirements of any cultivation as regards manuring could 

 be definitely ascertained by means of a chemical analysis of the 

 soil, this is not now believed to be correct. The necessary 

 elements may be present in the soil, and this may be certified 

 by means of chemical analyses, but they may not be " avail- 

 able/' This is to say, they may be locked up in a sufficiently 

 insoluble form. Instead, therefore, of the strong acids hitherto 

 employed in testing the soil, which broke down all opposition 

 and released locked-up elements, it is now more commonly the 

 practice to employ quite a weak solution of citric acid as a test 

 of what amounts of phosphoric acid and potash are present in 

 the soil in a form readily " available " (easily soluble). If a 

 weak solution of citric does not bring evidence of the presence 

 of potash and phosphoric acid, they are not present in the soil 

 in a form " available " to the roots and the bacteria present in 

 the soil. 



As a matter of fact, here again with regard to what should be 

 applied to land in the form of manures there is a great deal oi 

 obscurity and indecision. Like the managers who chose about 

 a dozen different planting distances on their estates in the hope 



