200 



The Rothamsted Grass Experiments. 



It is now clear that only a comparatively small proportion 

 of the nitrogen supplied in farmyard manure is recovered in 

 the increase of crop. The residue actually determined in the 

 soil is very large ; and it is possible that the whole of the 

 nitrogen existing as nitric acid, especially in the subsoil, is 

 not accounted for by the soda-lime determinations. It is 

 very remarkable, however, that, notwithstanding this great 

 ascertained accumulation, and the annually renewed supply 

 by manure, larger quantities of corn, or of straw, or of both, 

 and also of hay, are every year obtained by the use (in con- 

 junction with mineral manures) of much less than half as 

 much nitrogen applied as ammonia-salts or as nitrate of soda. 

 The wheat plots so manured, and so yielding, at the same 

 time show less than two-thirds as high a percentage of nitro- 

 gen in the first 9 inches of depth. 



TABLE LIII. EXPERIMENTS ON WHEAT. ESTIMATED NITROGEN 



SUPPLIED IN THE MANURE, RECOVERED IN THE INCREASE OF CROP, 

 DETERMINED AS EESIDUE IN THE SOIL, AND NOT RECOVERED IN 

 EITHER THE INCREASE OR THE SOIL, TO THE DEPTH OF 27 INCHES. 



But, according to the estimates, besides the actually- 

 determined large residue within the soil, there was also in 

 each case a very large amount of nitrogen unaccounted for, 

 either in the increase of crop or in the soil, to the depths 

 examined. Direct experiments have shown that the soil 



