128 



SOIL CONDITIONS AND PLANT GROWTH 



A very similar result was obtained by King and Doryland (148) in 

 their numerous counts. Neither temperature nor moisture changes 

 produced any systematic increases in numbers, and the only factor 

 that did have this effect was deep ploughing. 



Using Remy's method of physiological grouping Lohnis and 

 Sabaschnikoff at Leipzig (i88) obtained a curious and wholly unex- 

 pected set of curves suggesting some remarkable seasonal relationships. 

 The urea-decomposing power, nitrifying power, nitrogen-fixing power 



Rate of Decomposition of Cyanamide 

 (Lohnis) . 



1904 

 1907 



\ 

 \ 





\ 



\ 



Mar Apr. May June July Aug. Sept Oct 



Le ReVeil de la Terre (Miintz and Gaudechon) 

 Rate of Nitrification. 



IGOO 



1200 



80O 



400 



Feb April May Feb. April 



14 Terre 9 Terrecuc 



Bacterial numbers in soil : plots IB and 48. Cropped with millet : unmanured. (The 

 curve showing moisture content is very similar to that for 43.) (Conn). 



FIG. 7. Bacterial activity in soils at different seasons of the year. 



and to a less extent the denitrifying power all reached a maximum in 

 spring, a minimum in summer and a maximum again in September. 

 Muntz and Gaudechon (2090) also showed by a somewhat different 

 method that the nitrifying power is at a maximum in spring. Conn 

 (710) obtained a similar curve for the bacterial numbers in his plots, 

 the numbers of bacteria being high in February when the land was 

 frozen, they fell in summer but rose again in autumn. (Fig. 7). 



