92 THE POPULAR SCIENCE MONTHLY. 



ceived in the annual rain-fall is approximately balanced by the amount 

 lost by the land, as nitrates in the drainage-water." 



Where the great decrease in the yield of nitrogen was observed, in 

 the case of the root-crops which were grown for thirty-one years in 

 succession, the soil at the end of twenty-seven years was found to con- 

 tain a smaller percentage of nitrogen than any other arable land of 

 the farm. 



In the experiments on the mixed herbage of permanent grass-land, 

 " the soil of the plot which, under the influence of a mixed mineral 

 manure, including potash, had yielded such a large amount of legu- 

 minous herbage, and such a large amount of nitrogen, showed, after 

 twenty years, a considerably lower percentage of nitrogen than that 

 of any other plot in the series." 



The soil of the garden-plot, which gave so large a yield of clover 

 over a period of twenty-seven years, was analyzed at the end of 

 twenty-six years, and Dr. Gilbert remarks, in regard to the loss of 

 the nitrogen of the soil, that " the diminution, to the depth of nine 

 inches only, represents, approximately, three fourths as much as the 

 amount estimated to be taken in the clover in the intervening period ; 

 and the indication is, that there has been a considerable reduction in 

 the lower depths also." 



When nitrogenous manures were applied in the form of ammonia 

 salts or nitrate of soda there was little or no decrease in the nitrogen 

 of the soil, and in some cases there was an actual gain ; but the loss 

 from drainage was much greater, and it increased with each increment 

 of the manures applied under the same conditions. On plots receiving 

 43, 8G, and 129 pounds, respectively, of nitrogen in the form of am- 

 monia salts, mostly applied in the autumn, the estimated loss of nitro- 

 gen by drainage was 19, 31, and 42*4 pounds ; " and with 86 pounds 

 of nitrogen applied without, or with different mineral manures, the 

 estimated loss ranged from 31 pounds with the most liberal manure to 

 43 - 2 pounds with the ammonium salts continuously used alone." 



The nitrogen of barn-yard manure, which from its comparative in- 

 solubility is more slowly available for purposes of plant-growth, was 

 not lost by drainage to the same extent as the chemical manures, and 

 there were decided indications of considerable accumulations of it in 

 the soil. The nitrogen applied in manures is not all accounted for in 

 the amounts removed in the crop, lost by drainage, and stored up in 

 the soil ; and it therefore seems probable, in the absence of any other 

 known disposition of it, that the estimated losses by drainage, based 

 on the materials discharged by the tile-drains, are altogether too low. 

 As the drainage -waters, with the substances they hold in solution, pass 

 from the upper to the lower strata of the soil, we can not avoid the 

 conclusion that a large proportion must pass below the level of the 

 drains without entering them. The drains of the experimental wheat- 

 fields are nearly twenty-five feet apart, and the underlying chalk at the 



