CANE SUGAE. 



A point of very great interest in connection with cane growing and one 

 which has not, so far as the writer is aware, been thoroughly investigated, is 

 the lime : magnesia ratio best suited for the cane. Eor cereal crops generally, 

 for rice, and for such as have a large leaf development, evidence has been 

 brought forward by Loew 11 and his pupils that the lime should be in excess of 

 the magnesia in proportion from 1*5 to 2 times as great. In the absence of 

 any evidence to the contrary it may perhaps be taken that a similar ratio holds 

 for the cane. That an excess of magnesia has a deleterious effect on the cane 

 has been shown by Eckart, 12 who irrigated cane in tubs with both lime and 

 magnesia chlorides, and found a much better growth when the lime was in 

 excess of the magnesia than when the quantity of these two bodies was 

 mearly the same. 



Quite recently Loew 13 in Porto Rico has gone further into the subject in 

 special reference to the cane ; in that island he has found the soils containing 

 an excess of magnesia over lime. He quotes an instance of a cane soil suffering 

 from acidity, stiffness and an excess of magnesia over lime where an applica- 

 tion of 3000 Ibs. lime per acre increased the yield of cane 57 per cent. He 

 also writes : " The most favourable ratio of lime to magnesia in the soil for 

 cane will very probably be as 2-1, if both are present in an equal state of 

 availability. This can be inferred from experiments with maize by 

 Bernadini." 



The hypothesis of Loew, though carefully elaborated, is not accepted by 

 many agronomists; it has been followed up chiefly in Japan by Aso and 

 others. The lime-magnesia ratio must apply to the soil water or to readily 

 soluble forms in the soil ; a hydrochloric acid soil extract showing an excess 

 of magnesia over lime would not be sufficient to condemn a soil on Loew's 

 hypothesis. It is of interest to note that in some Demerara soil water, 

 Harrison 14 has found that with sulphate of ammonia manuring the molecular 

 ratio of calcium-magnesium was 1 : -77 ; with nitrate of soda manuring it was 

 1 : T52, and with no manuring 1 : 2*40, and with no cultivation 1 : 2- 57. 



Yields of cane had become very deficient in the second and third cases but 

 Harrison does not commit himself to attach any special significance to these 

 ratios. 



Distinction between Forms of Nitrogen. Nitrogen is con- 

 tained in manures as nitrate, ammonium salts, or as organic nitrogen ; these 

 differ in their effect as regards ' availability.' It was formerly held that the 

 plant absorbed nitrogen as nitrate ; latterly it has been clearly shown that 

 ammonia salts may be directly assimilated. The organic forms of nitrogen 

 have first to be acted on by soil organisms before they are of use to the plant, 

 and hence they are not so rapidly available as nitrate or ammonia salts; 

 cyanamide, too, is not at once available, and has to be acted on by soil 

 organisms, but field experiments have shown that this substance has a high 



70 



