COMPOSITION OF DRAINAGE WATERS 237 



crops. Their growth is almost completed before nitrification 

 has reached its greatest activity (from flowering time onwards 

 the cereals take no more nitrogen from the soil), and being 

 harvested in August or early September, they leave the ground 

 bare at a time of rapid nitrate formation, thus exposing it to 

 all the risks of washing away by the autumnal rains. 



VI. OTHER CONSTITUENTS OF DRAINAGE WATERS. 



Complete analyses of the mineral constituents of the waters 

 draining from the various Broadbalk plots were made at various 

 times by the late Dr Voelcker and by Sir Edward Frankland ; 

 these analyses still constitute almost our only information as to 

 direct losses of the land by drainage. 



Table LXXXVI. gives an average of the five analyses 

 made during the years 1866, 1867, and 1868. 



TABLE LXXXVI. Composition of Drainage Waters from the Broadbalk 

 Wheat Plots, in parts per million (Dr A. Voelcker}. Mean of jive (or 

 fewer} Collections December 6, 1866 ; May 21, 1867 ; January 13, 

 April 21, and December 29, 1868. 



As regards constituents of manurial value, it has already 

 been noted that practically no nitrogenous compounds occur 

 in drainage water except the nitrates ; phosphoric acid is 



