vii.] CULTURES FOR SOIL INOCULATION 209 



be inoculated or not. In such cases inoculation can 

 only be beneficial if the bacteria introduced either 

 belong to a more vigorous race of nitrogen fixers 

 than those normally present in the soil or are more 

 specifically adapted to that particular crop. It has not 

 as yet been conclusively demonstrated that such im- 

 proved races can be cultivated in the laboratory, or that 

 they can maintain themselves in the soil in competition 

 with the kindred organisms already present. It should, 

 moreover, be borne in mind that even if such improved 

 races of the nodule-forming organism can be introduced 

 to the plant, the improvement they can produce in the 

 yield is likely to be something of the order of a ten per 

 cent, increase, a gain which is only really perceptible 

 after careful and continued field experiments, and one not 

 to be detected by the ordinary farmer's eye. Of a very 

 different order are the results attained by inoculation 

 when the land contains none of the appropriate 

 organisms ; inoculation will then change a stunted, 

 sickly-looking growth into a profitable crop. It is only in 

 special cases that land devoid of the nodule organisms 

 is to be met with, most commonly when land is being 

 brought under cultivation for the first time, as in 

 breaking up a virgin soil or in reclaiming heath and bog 

 land. Such peaty and heathy soils, which are devoid of 

 carbonate of lime, rarely carry any leguminous plants 

 the nodules of which could supply the necessary bacteria 

 to farm crops like clover and lucerne ; when such land 

 has been reclaimed and limed an inoculation is advisable 

 before sowing a leguminous crop. 



Similarly when the cultivation of such leguminous 

 crops as lucerne or even sainfoin is being extended into 

 districts where they have not been grown previously, an 

 inoculation is often necessary before the roots will nodu- 

 late freely and the plant make its proper growth. Lucerne 



P 



