THE MANURING OF THE CANE 93 



time be observed are probably due to different degrees of maturity or to other 

 uncontrollable factors vitiating the comparison. 



The Ash of a Plant in Relation to Manuring. It has been thought that 

 the analysis of the ash of a plant and the agricultural balance sheet would 

 give information as to the proper combination of manures to apply ; this idea 

 demands that for any plant there is one particular ash analysis which is 

 most suited for it. The variation, however, is so great that no " best ash " 

 for the cane can be obtained, and this captivating hypothesis breaks down 

 on subjection to scrutiny, or rather is not supported, as regards the cane, 

 by sufficient evidence. It is conceivable, however, that an ash analysis 

 snowing a low proportion of, say, lime might point to a deficiency of available 

 lime in the soil ; on the other hand, a deficiency of lime in the soil might be 

 reflected in small crops rather than in a low percentage of lime in the ash. 



Connected with this subject is the " Analysis of the Soil by means of the 

 Ash " ; this point has been recently studied by Hall, 22 who thus summarizes 

 his results, obtained, of course, in a temperate climate (England), but none 

 the less generally applicable : 



i. The proportion of phosphoric acid and of potash in the ash of any given 

 plant varies with the amount of these substances available in the soil, as measured 

 by the response of the crops to phosphatic or potassic manures respectively. 



2,. The extent of the variation due to this cause is limited, and is often no 

 greater than the variations due to season, or than the other variations induced by 

 differences in the supply of non-essential ash constituents -soda, lime, &c. 



3. The fluctuations in the composition of the ash are reduced to a minimum in 

 the case of organs of plants, which, like the grain of cereals or the tubers of potatoes, 

 are manufactured by the plant from material previously assimilated. 



4. The composition of the ash of the cereals is less affected by changes in the 

 composition of the soil than is that of root crops like swedes and mangels. 



5. The composition of the ash of mangels grown without manure on a particu- 

 lar soil gives a valuable indication of the requirements of the soil for potash manur- 

 ing. Similarly, the phosphoric acid requirements are well indicated by the compo- 

 sition of the ash of unmanured swedes, though in this case determination of the 

 citric acid soluble phosphoric acid in the soil gives even more decisive information. 



6. Pending the determination of phosphoric acid and potash " constants " for 

 some test plant occurring naturally on unmanured land, the interpretation of soil 

 conditions from analyses of plant ashes is not a practicable method by which 

 chemical analysis of the soil can be displaced. 



The effect of the soil on the composition of the ash of the cane is well 

 shown in some observations of Burgess 23 dealing with Hawaiian soils quoted 

 below : 



Burgess considers that potash manuring is indicated as advisable for the 

 soils of the Puna-Hilo district, where there is a very distinct correlation 

 between the potash in the soil as indicated by analysis and that found in 

 the molasses afforded by canes there grown. 



