11.] NITRATE OF SODA—SULPHATE OF AMSfOMA 65 



grown Nvith sulphate of ammonia and nitrate of soda 

 respectively. On the grass plots at Rothamsted, for 

 example, where the manuring has now been repeated 

 year after year for fifty years, very distinct types of 

 herbage have associated themselves with the two 

 manures. Putting aside the prevalence of sorrel as 

 due to the acid comlitions, the characteristic grasses on 

 the plots receiving ammonium salts possess a shallow- 

 rooted habit, e.g., sheep's fescue and sweet vernal grass, 

 while the nitrate of soda has favoured deeply rooting 



Table XVI.— Ammonium Salts r. Nitratb of Sopa, Rothamsted. 



grasses like the soft brome. Actual examination of 

 the subsoil shows that the roots have penetrated much 

 deeper on the nitrate of soda than on the ammonia 

 plots, the roots having followed the soluble nitrate 

 down into the soil in the one case, whereas in the other 

 they remain near the surface where the nitrogenous 

 material has been accumulated. We may apply the 

 clue thus obtained to interpret the comparative results 

 given by the two manures on other crops ; wheat, for 

 example, a deep-rooted crop, may be contrasted with 

 barley, which feeds near the surface, but agrees again 

 with mangolds, another deep-rooted crop. 



It will be seen that with the deep-rooting crops, 

 wheat and mangolds, nitrogen in nitrate of soda gives 



