phosphorus being removed from plot u in the crops produced as is 

 applied during the five years, as is easily determined by computa- 

 tion. It is impossible that the crop yields will be permanently 

 maintained under this system, unless the partially depleted sur- 

 face soil is removed by erosion at least in corresponding rapidity as 

 the phosphorus is removed in crops. 



On the other hand, nitrogen must be the limiting element where 

 30 pounds of phosphorus were used; but, wherever the amount of 

 phosphorus was increased, the nitrogen was also reduced, so that 

 it is impossible to determine what effect is produced either by in- 

 creasing the phosphorus or by reducing the nitrogen. 



The experiments on plots 14 and 15 are essentially variations in 

 amount used of a complete fertilizer; but on 15 the fertilizer is 

 applied for wheat, and on 14 for corn and wheat, while on all other 

 plots the fertilizers are applied in three portions, for corn, oats, and 

 wheat. (The manure is applied in two equal portions, for corn 

 and wheat.) 



The comparison of the different forms of nitrogen is valuable, 

 because nitrogen is the limiting element on those plots; while the 

 comparison of different phosphates is likewise so planned that 

 phosphorus is the limiting element. 



The insoluble phosphorus in raw bone, basic slag, and tankage 

 is reckoned at 10 cents a pound. 



In the main the Ohio experiments reported in Table 82 were 

 designed to supply about the same quantities of nitrogen, phos- 

 phorus, and potassium, as were removed in the average crops pro- 

 duced by farmers on the ordinary land in that section of the state. 

 Where complete fertilizers are used by farmers in a rotation of 

 this kind, about 200 pounds per acre may be applied for corn and 

 again for wheat, making 400 pounds for the rotation. The most 

 common composition is the 2-8-2 goods, containing 2 per cent 

 of ammonia (NH 3 ), 8 per cent of " available phosphoric acid" 

 (P 2 O 5 ), and 2 per cent of potash (K 2 O); or, in the 400 pounds, 

 about 7 pounds of nitrogen, 14 pounds of soluble (and 3 pounds 

 of insoluble) phosphorus, and 7 pounds of potassium. In other 

 words, the total amounts applied in four or five years would furnish 

 enough nitrogen for one 5-bushel crop of corn, enough phosphorus 

 for one 7o-bushel crop, and enough potassium for one lo-bushel 



