H. I). llimiiiNsoN Oo 



dcscribod by Harrison and \Vaid(-:f) are tv])ical, wliere the applicationof 

 saccharine material has been quite inefi'ective in promoting greater 

 fertility. 



In many of these cases it is ditHcult to account for the absence of any 

 specific effect of the treatment on crop yield, owing to the lack of 

 information as to the precise conditions under which the experimonis 

 were carried out. The possibility is not excluded, however, that this 

 ineffectiveness is the resultant of two distinct sets of changes, luiniely, 

 the beneficial effects which have been discussed above, and the dis- 

 tinctly injurious ones which have been observed by Hiltner(2i), von 

 Seclhorst(25), Stutzer(2(i). P)artels(-7) and others to resiUt from the admix- 

 ture of straw, green manures and so forth, with the soil. The tendency 

 towards divergent results has been recognised by Peck (28) who states 

 that harmful effects are likely to attend the application of molasses at 

 frequent intervals to growing sugar cane, but that when applications 

 are made some weeks prior to the introduction of a crop, beneficial 

 results may be obtained. 



The experiments described in the following pages alford additional 

 evidence of each of these effects. The incorporation of such substances 

 as sugar, starch, or plant residues with the soil is likely to give rise to 

 two opposite processes, one of which results in a diminution, and the 

 other in an increase of the fertility of the soil. Whether the one pre- 

 ponderates over the other, or an equilibrium is attained, depends largely 

 on the quantity and type of material applied, the prevailing tenqjerature, 

 the interval before the introduction of a crop, and the presence of the 

 specific micro-organisms. 



In any case the destructive changes come first into operation but 

 their relative intensitv and the period of persistence are increased by low 

 temperatures. High temperatures by permitting of the entrance and 

 subsequent predominance of constructive bacterial changes, tend to 

 limit the extent and persistence of soil losses. 



The experiments show that the introduction of a crop immediately 

 after the incorporation of material containing carbohydrates will result 

 in decreased yields. If a long period is allowed to elapse before the crop 

 is sown this decrease may be only slight or entirely absent in spite of low 

 temperatures. If the soil temperature is high and sufficient time is given 

 before a crop is sown, adverse changes are likely to be reduced to a 

 minimum and favourable after-effects may be anticipated. 



The autumn application of plant residues, strawy material, etc., may 

 therefore be expected to lead to beneficial changes; spring applications 



