THE MAINTENANCE OP SOIL FERTILITY 555 



of a soil is obviously impossible unless some knowledge is at 

 hand regarding tlie losses and additions which a soil sustains 

 in the course of a definite rotation. Fortunately, some fairly 

 reliable data have already been presented regarding the re- 

 moval of soil constituents under controlled conditions. The 

 Cornell lysimeter tanks, bearing a rotation of maize, oats, 

 wheat, and two years of hay, offer very satisfactory informa- 

 tion (paragraphs 95 and 163). The losses covering a ten-year 

 period are expressed in pounds to the acre a year. The soil is 

 a Dunkirk silty clay loam. 



While such figures are probably open to considerable error 

 and obviously would not apply with any degree of accuracy 

 to a light soil, they indicate in a general way the magnitude 

 and order of the losses that may be expected from such a soil 

 under the conditions specified. 



Table CXXvIII 



losses from a dunkirk silty clay loam soil kxpbessed in 



pounds to the acre a year over a ten- year period. 



rotation: maize, oats, wheat and two years 



hay. cornell lysimeter tanks. 



Source of Loss 



N 



PA 



K^O 



CaO 



SO, 



Drainage (par. 163).... 

 Cropping (par. 163) .... 

 Atmosphere (pars. 

 220 and 233)^ 



7.3 

 70.5 



• 



trace 

 43.5 



68.7 

 105.4 



845.9 

 24.3 



108.5 

 41.0 



Total 



77.8 



43.5 



174.1 



370.2 



149.5 







The organic carbon in this soil over the ten-year period was 

 reduced at the rate of approximately 1 per cent, a year.^ This 

 is equivalent to a reduction in organic matter of about 1200 



^The largest loss of carbon is probably to the atmosphere as carbon 

 dioxide. The other avenue of loss is in the drainage water. 



^Lipman and Blair report a reduction of organic carbon of .74 per 

 cent, a year over a period of ten years on Sassafrass loam in New 



