THE MICRO-ORGANIC POPULATION OF THE SOIL 2^ 



effect of added organic matter is to increase supplies of energy 

 and therefore to increase bacterial numbers. The question 

 whether nitrate supplies will be increased depends on the pro- 

 portion of nitrogen present in the added matter : if it is rich 

 in nitrogen a considerable amount of nitrate may be formed ;^ 

 if it contains no nitrogen there arises an actual loss of nitrate 

 though there may be a fixation of gaseous nitrogen. The 

 special case of farmyard manure has been much studied.^ 



Effects of Lime, Calcium Carbonate, and Magnesium Car- 

 bonate. — Numerous papers have been written on this subject 

 and the results are at first sight somewhat contradictory. 

 Much of the work has been done on acid soils, where, as 

 might be expected, benefit has been derived from neutralisa- 

 tion. F. E. Bear^ finds that calcium carbonate greatly in- 

 creases the numbers of bacteria in acid soils once the neutral 

 point is passed, but not before : it much increases ammonifi- 

 cation and nitrification up to the neutral point, but to a less 

 extent afterwards. In neutral soils, however, less concordant 

 results have been obtained ; some investigators have observed 

 detrimental effects from further addition of calcium carbonate,* 

 while others have obtained only beneficial results,* bacterial 

 numbers, ammonifying power and nitrifying power all being 

 increased. Magnesium carbonate may be more effective than 

 calcium carbonate in small quantities, but it is toxic in larger 

 amounts.^ Lime in excess of a certain amount acts as a 

 sterilising agent (i39<:). 



1 For the effect of the N : C ratio see P. E. Brown and F. E. Allison, Soil 

 Set., 1916, I, 49-75 ; and also H. B. Hutchinson and J. Clayton (139/). 



2 P. 193, also T. G. Temple, Georgia Rpt., 1916 ; Greaves and Carter, 

 jfourn. Ag. Res., 1916, 6, 889. 



^SoilSci., 1917. 4. 433. 



* E.g. J. G. Lipman, P. E. Brown, and I. L. Owen, Centr. Bakt. Par., 1911, 

 30, 156-181. 



' S. S. Peck, Hawaiian Sugar Planters^ Chem. Bull., 34, 1911 ; P. E. Brown, 

 Iowa Research Bull., 2, 1911 ; Bull., 44, 1918 ; J. E. Greaves, Soil Sci., igi6, 

 2,443-480; H. L,. Fulmei, yourn. Agric. Res., 1918, 12, 463-504, although he 

 obtained harmful effects on nitrification. 



«J. G. Lipman and P. E. Brown, N.y. Agric. Expt. Sta. 2Sth Ann. Rept., 

 141-204 : C. B. Lipman and P. S. Burgess, Journ. Agric. Sci., 1914, 6, 484-498 ; 

 H. L. Fulmer, Journ. Ag. Res., 1918, 12, 463. 



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