264 SYSTEMS OF PERMANENT AGRICULTURE 



ing the entire twelve years, and Table 43 & g ives the average re- 

 sults for the last four years. 



TABLE 43. PENNSYLVANIA EXPERIMENTS WITH DIFFERENT FORMS OF PHOS- 

 PHORUS: YIELDS PER ACRE: AVERAGE OF DUPLICATE PLOTS 



(a) Average of Twelve Years' Work 



(V) Average of Last Four Years 



By computation it will be found that the cost of the nitrogen 

 and the potassium for four years was $24.06 per acre ($25.26 on the 

 bone-meal plots); while the phosphorus for four years cost $3.36 

 in soluble or reverted form, $3.50 in bone ($4.70 including the cost 

 of nitrogen), and $1.05 in the raw rock phosphate, at the prices 

 mentioned in Table 24. 



At safe prices for increase in produce based upon zo-year aver- 

 ages for the corn belt : corn 35 cents a bushel, oats 30 cents, wheat 

 70 cents, and hay $6 (about $3 per ton being allowed for 

 stacking, baling, marketing, and loss), the value of the increase 

 produced in four years by $24 worth of nitrogen and potassium is 

 $11.72 per acre as an average of the twelve years, and $10.19 per 



