Knowledofe. 



With which is incorporated Hardwicke's Science Gossip, and the lUustrated Scientific News. 



A Monthly Record of Science. 



Conducted by \\"ilfred Mark Wel.b. F.L.S., and E. S. Grew, M,A. 



APRIL, 1 y 1 1 . 



SOIL BACTERIA AND CROP PRODUCTION. 



Bv H. B. HUTCHINSON. D.Sc. 



During the last thirty years the methods of 

 estimating soil fertility have undergone considerable 

 change. The crude chemical method of determining 

 total soil constituents has given place to one more 

 nearly appro.ximating that of the plant itself, and the 

 value of the results so 

 obtained has been con- 

 siderabh' enhanced by 

 the consideration of 

 the mechanical com- 

 position of any given 

 soil. 



Within the same 

 period the old concep- 

 tion of the soil as being 

 merely a store - house 

 of plant food has given 

 way and soil is now- 

 regarded rather as a 

 medium in w h i c h 

 myriads of micro- 

 organisms e.xist and 

 e.xert their influence. 

 The dissolution of 

 plant and animal re- 

 mains and the con- 

 sequent production of 

 substances capable of 

 subserving plant gro^\■th 

 bacteria. Smce nitrogen i 

 soil constituent, it is not 



Figure 1. 



Wheat Growing in Partially-sterilized Soils. 



Left to Right: Untreated, Tolnened. and Heated Soil. 



is the work of soil 



is the most valual)lc 



surprising that thi' 



organisms responsible for various reduction anti 

 oxidation changes such as amiuonilication. nitri- 

 fication, nitrogen-fixation, and so on. have received 

 most attention, while those inducing cellulose fenuen- 

 tation and changes in sulphur and iron cornpounds 

 have been less studied. 



Although the activities of this micro-flora result 

 in the production of plant food, it would be fallacious 

 to assume that this represents in any adequate 

 measure the total changes occurring in the soil. 

 Decomposition of highly-organised nitrogenous 



bodies mav be accom- 

 plished, nitrates formed, 

 -_. and nitrogen iua\- be 

 fixed, but a portion of 

 this elaborated material 

 may be lost again by 

 the action of other 

 organisms. S\-mbio- 

 sis and antagonism 

 between soil organisms 

 have been obser\-ed in 

 man\- instances, and 

 recent investiga- 

 tions indicate in a 

 striking manner the 

 far-reaching effect of 

 another factor inimical 

 to bacterial growth. 



The extent to w hich 

 this factor exerts an 

 influence is shown by 

 results obtained from 

 experiments on the 

 partial sterilisation of soils. Numerous workers 

 ha\-e shown that if a soil is subjected to the action 

 I if lu-at or of mild antiseptics, an increase in the 

 fertilit\- of that soil ensues. In the former case high 

 temperatures (95" to 100° C.) were adopted, and no 

 doubt led to a certain amount of chemical decom- 

 position of some of the soil constituents. Direct 

 chemical action, however, is insufficient to account 

 for the increase in fertilitv. 



123 



