THE MAINTENANCE OF SOIL FERTILITY 557 



Table 0A.A.I3L 



ESTIMATED ADDITIONS THAT MIGHT OCCUR TO A SOIL UNDER A 



ROTATION OP MAIZE, OATS, WHEAT, AND TWO YEARS HAY. 



EXPRESSED IN POUNDS TO THE ACRE A YEAR. 



Source of Addition 



N 

 12.5 



25.0 

 37.5 



P^O. 



K2O 



CaO 



SO3 



Rain-water (pars. 236 and 264) 

 Free fixation by soil organisms 

 (par. 238) 







— - — 



" 



65.0 



Crop-roots and residues ^ 





Total 



65.0 







use of farm manure and a green-manure on the soil in question. 

 The green-manure is leguminous and is applied once during 

 the five-year rotation. 



Table CXXX 



further additions that might be made to the five-year 



rotation on dunkirk silty clay loam, expressed in 



pounds to the acre a year. 



Additions 



N 



P2O, 



K2O 



CaO 



SO, 



Organic 



Matter 



Farm manure ^ 



Leguminous green- 

 manure ^ 



21.1 

 20.0 



21.7 



31.6 



7.3 



12.4 



1000 

 600 







Total 



41.1 



21.7 



31.6 



7.3 



12.4 



1600 







* Important because of the additions of organic matter that occurs 

 thereby. 



* It is estimated that of the crops removed and fed or used as bedding, 

 only 30 per cent, of the N, K^O, CaO and SO3, 50 per cent, of the PgOs 

 and 25 per cent, of the organic matter reach the soil as farm manure (par. 

 294). The crops removed carried about 4000 pounds of organic matter 

 to the acre. 



^The green-manure is estimated as 4000 pounds of air-dry matter 

 carrying 100 pounds of nitrogen, which is considered as fixed from the 

 air. This should yield SOOO pounds of soil organic matter. 



