FARMYARD MANURE 175 



required to furnish 12 Ib. of nitrogen, and, 

 assuming the price of the nitrate of soda 

 to be 10 per ton, the outlay on 77 Ib. would 

 be 6s. lOd. Similarly, to obtain 12 Ib. of 

 potash we might purchase 100 Ib. of kainit 

 at a cost of about 2s. ; and to obtain 5 Ib, 

 phosphoric acid we might select a 30-per- 

 cent. -soluble superphosphate costing 2, 15s. 

 a ton, of which 37 Ib. would be necessary, 

 involving an outlay of lid. Adding these 

 figures together, we obtain a theoretical 

 value for farmyard manure of 9s. 9d. per 

 _ton, a sum that is much in excess of its 

 market price. In point of fact, certain con- 

 siderations combine greatly to reduce the 

 value of farmyard manure below its theo- 

 retical level. Thus it has been found at 

 Rothamsted that only one-fourth to one-third 

 of the nitrogen supplied in farmyard manure 

 is utilized by plants, as contrasted with 

 three-fourths in the case of the nitrogen of 

 nitrate of soda. If the fate of the phosphoric 

 acid and potash could thus be followed up, 

 it would probably be found that their 

 availability in farmyard manure is no greater 

 than that of the nitrogen. Then, again, 

 farmyard manure is a very dilute substance, 

 so that large quantities have to be applied 

 to the land to secure a full crop, and the 



