Unexhausted Residue of Manures. 31 



year. When ammonia- salts were applied, the greater portion 

 of the nitrogen remained unrecovered as increased yield in 

 the crop for which it was employed. The unexhausted 

 residue of nitrogen supplied as manure was but very partially 

 and very slowly recovered as increased yield in succeeding 

 years, even when followed by the liberal application of such 

 mineral manure as was very effective when used in conjunc- 

 tion with newly applied ammonia-salts. Mineral constituents 

 supplied in the soluble condition in the fifth and seventh 

 years of the experiments, though giving very little increase 

 when in the latter year they were used alone, continued to 

 increase the effect of ammonia- salts afterwards annually 

 applied for thirteen consecutive years. A given amount of 

 ammonia- salts gave very different amounts of increase, 

 according to the supply of available mineral constituents 

 within the soil, giving very much more when mineral manures 

 were supplied in the same, than in the preceding year, not- 

 withstanding that, in the latter case, there could be no 

 deficiency, though, doubtless, less favourable condition and 

 distribution of the mineral constituents. The same mineral 

 manures which were very effective when supplied in conjunc- 

 tion with ammonia-salts, gave very little increase of produce 

 when used alone year after year for twelve years, although 

 following an excess of ammonia-salts applied in preceding 

 years ; and they gave very little more when they were applied 

 every year succeeding an excess of ammonia- salts applied in 

 the immediately preceding year. The unexhausted residue 

 from previous mineral manuring, though it served as an 

 effective reserve against exhaustion, had little or no effect in 

 increasing the growth of wheat without the aid of available 

 nitrogen provided within the soil. An unexhausted residue 

 from previous nitrogenous manuring had also but little 

 influence upon the immediately succeeding crops, even when 

 aided by the application of mineral manures. 



The bearing of the foregoing facts upon the question of 

 the probable influence on the mineral wealth of our soils of 



