84 CHAPTER VI 



are associated, due to biological, chemical, and physical effects which its component 

 parts have in a given soil, variations in the composition of the mixture beyond 

 certain limits may materially influence crop yields. 



4. A more definite knowledge concerning the amounts and proportions of 

 fertilizer salts to use in a mixture for best results would on some soils yield pro- 

 nounced profits, while a lack of such knowledge may in some cases result in a loss, 

 especially when soluble salts are employed. 



5. The greatest loss from the use of improper mixtures of fertilizers is apt 

 to occur on acid soils, and in such cases considerable risk is involved from the 

 continued application of mixtures containing ammonium sulphate, sulphate of 

 potash, and acid phosphate, when lime dressings are not previously made. 



6. While the chemical and physical analysis of a soil will usually prove 

 of value in indicating the best cultural methods to follow in maintaining or improving 

 its fertility, and may also indicate in a geneial way certain of the plant-food de- 

 ficiencies in given cases, it cannot afford definite information as to the amounts or 

 proportions of ingredients in fertilizer mixtures which will give maximum returns. 



7. It is possible that the data from more extended field experiments with 

 a large variety of soils, when reviewed in connection with the comparative analysis 

 of the soils, using both weak and strong acids as solvents, may indicate a somewhat 

 definite relationship between the analytical figures and the order of importance 

 which phosphoric acid and potash should assume in cane fertilizers in given cases. 



8. It would appear that analysis of sods, with more special reference to 

 their physical qualities, reaction and content of organic matter, nitrogen, and 

 more readily soluble lime, may, with due consideration of the water supply and 

 climatic conditions, be relied upon to indicate such manurial treatment as will 

 result in a profit, although thej' will not aSord definite information as to the weights 

 and proportions cf ingiedients in fertilizer mixtures which will result in maximum 

 efiiciency. 



9. Nitrogen is the most important element to be considered in the fertilization 

 of the sugar cane in the Hawaiian Islands, and when applied in mixed fertilizers 

 some risk of reduced efiSciency is entailed if either the potash or phosphoric acid 

 (in the form of soluble salts) is made to exceed the weight of this element. 



10. Unless, through past local experience or carefully conducted field tests, 

 it has been definitely determined that a modified formula may be expected to give 

 greater yields, it is safer, when applying nitrogen, potash and phcsphoric acid 

 in the form of soluble salts, to have the mixed fertilizer contain even quantitie." 

 of these elements, which are not to exceed 60 lbs. per acre in the case of each element. 



11. Field tests with fertilizers whose ingredients are mixed in varying pro- 

 portions will, if such experiments are accurately and scientifically conducted 

 through a sufficient period, give the most reliable information as to the best 

 manurial practice. Such experiments should be laid out in very long, narrow, 

 parallel and contiguous plats or strips, with the untreated check areas lying 

 immediately adjacent to the fertilized cane. 



12. The great importance of ' resting ' fields in rotation on Hawaiian planta- 

 tions, and growing iipon them leguminous crops is very clearly indicated. This 

 applies more particularly to the irrigated plantations, where the supplies of organic 

 matter are in the majority of cases becoming greatly reduced through successive 

 tillage operations in a comparatively arid climate, and by the favourable conditions 

 created for bacterial activity through regular irrigations under uniformly high 

 temperatures." 



More recent experiments summarized by Larsen^^ have given rather 

 different results. In some the appHcation of readily available nitrogen 

 alone gave as great a crop as when potash and phosphates were also used. 

 In others the greatest benefit followed from the application of a complete 

 manure. Variation in the soils themselves and the residual effect of previous 

 heavy applications of complete mixtures are possible disturbing factors. In 

 some of the later experiments there, the maximum money benefit from readily 

 available nitrogen was not reached until as much as 300 lbs. nitrogen per 

 acre had been applied. 



Java.^^ — The very numerous experiments made in Java have nearly 

 all led to the conclusion that readily available nitrogen is the only manure 

 required to give the maximum return. Certain soils are, however, benefited 



