207 



corn and oats yielding 100 bushels, and one 

 acre of clover yielding four tons, includes for 

 the total crops : Potassium, 320 pounds ; mag- 

 nesium, 68 pounds; calcium, 168 pounds; 

 phosphorus, 77 pounds. 



"If only the grain, including a yield of 4 

 bushels an acre of clover seed, is considered, 

 the straw, stalks and hay being returned to 

 the soil either directly or in farm fertilizer- 

 then the loss per acre from four years of crop- 

 ping as above would be as follows: Potas- 

 sium, 51 pounds; magnesium, 16 pounds; cal- 

 cium, 5 pounds; phosphorus, 42 pounds. 



"The average annual loss by leaching from 

 good soils in humid sections is known by the 

 results of many analyses to be about as fol- 

 lows per acre: Potassium, 10 pounds; cal- 

 cium, 300 pounds ; phosphorus, 2 pounds. 



"The average annual loss of magnesium in 

 drainage water from good soils is probably 

 30 pounds or more an acre, but the data thus 

 far secured are inconclusive with respect to 

 that element." 



Thus, by arithmetic, it would appear accord- 

 ing to these figures that such a soil as the 

 Leonardstown loam would support only two 

 cycles of rotation, or eight years' cropping, so 

 far as its phosphorus in the upper strata is 

 concerned. 



