11 



At Kothamsted the ammonia salts applied to wheat pro- 

 duce no effect in the year following their application. At 

 Woburn, when nitrate of soda is applied to wheat, there is 

 almost an entire absence of effect in the second year. The 

 remaining experiments at Woburn show a very different 

 result. In some seasons the residues of the ammonia and 

 nitrate produce no effect, while in other seasons their effect is 

 very marked ; indeed, when ammonia salts are applied to 

 barley, fully one-quarter of the return from the manure falls, 

 on an average, in the second year. It will be observed that 

 in every case the subsequent effect is greater with the 

 ammonia salts than with nitrate. 



We have probably a key to the explanation of these results 

 in the character of the Woburn soil. As this soil contains very 

 little lime, the nitrification of the ammonia is probably delayed, 

 especially if the season be dry, and is not completed till the crop 

 has passed the stage in which it can make use of nitrates. In 

 the Kothamsted field the unused nitrates would be partly re- 

 moved by the drain-pipes during autumn or winter, or carried 

 to a depth at which they could no longer benefit a crop. At 

 Woburn there are no drainpipes; the unused nitrates would 

 thus, after harvest, retire into the subsoil, and may be brought 

 again to approach the surface by a rise in the water-level, or 

 possibly by capillary attraction. A rise of the water-level 

 in the subsoil is known in India and California to bring 

 about an accumulation of salts in the top soil. The 

 physical condition of a very fine uniform sand is also far 

 more favourable to considerable movements of soil solutions 

 than is the case with a tenacious clay, and a much greater 

 quantity of water will be raised by capillary action in such a 

 soil, though not to quite so great a height as the much smaller 

 quantity of water rising in a clay. The nitrate of soda, being 

 at once ready for assimilation, is more completely taken up 

 by the crop, and less remains for a second season ; and this 

 residue is far smaller with wheat than with barley, probably 

 owing to the earlier and deeper development of the roots in 

 the case of autumn-sown wheat. The return from residues 

 of ammonia salts and nitrates observed at Woburn is probably 

 exceptional, but the possibility of such a return should be 

 borne in mind. 



