THE MICRO-ORGANIC POPULATION OF THE SOIL 269 



Table LXX, — Effect of Acidulated Water on the Growth of Plants 

 AND Bacteria. Crowther and Ruston (71). 



At first sight this looks like a close relationship between 

 bacterial activity and plant growth. But the figures in the 

 last column show that the failure of the crop is not due to the 

 failure of the bacteria to produce ammonia and nitrate, for 

 relatively large amounts of these substances are left at the end 

 of the experiment. 



In similar manner the growth both of bacteria and of 

 plants may be helped by the same cause. This is more fully 

 discussed in the following section. Speaking generally, it is 

 found that the bacterial numbers increase as the intensity of 

 the farming increases. Thus Stoklasa and Ernest (273^) 

 found only i to 2 million organisms per grm, in their barley 

 land, 3 to 5 millions on the better treated sugar-beet land, 

 and 7 to 8 millions on the clover land. Again, the addition 

 of plant residues or of farmyard manure to the soil increases 

 the bacterial numbers by furnishing the organisms with addi- 

 tional food;^ it also increases the crop. Moorland soils 

 contain only few bacteria and are very unsuited to the growth 

 of most plants. But after cultivation and treatment with 

 lime and manures they become much better media both for 

 plants and bacteria. Fabricius and von Feilitzen (97^) found 



1 Examples are given by P. E. Brown, Iowa Research Bull., No, 13, 1913, 

 and by Heinze, Landw. yahrbiicher, 1910, 39; Erg&nz. Bd. 3, 314-343. 



