Continuous Application of Nitrogenous Manures. 99 



grain and ISfcwt. of straw. In other words, whilst the 

 increase of produce by the mixed manure alone averaged, over 

 twenty years, only 6| bushels of grain and 2J cwt. of straw 

 per acre per annum, the increase by this comparatively small 

 quantity of ammonia-salts alone averaged over the same 

 period 11| bushels of grain and 6| cwt. of straw. Comparing 

 the effects of ammonia-salts with those of the same quantity 

 of nitrogen in nitrate of soda, the latter gave an "average 

 annual increase of 5J bushels of grain and 4fcwt. of straw 

 over the former. Owing to the greater solubility and more 

 rapid distribution in the soil and subsoil of the nitrate or 

 its products of decomposition, it is more liable to loss by 

 drainage when there is an excess of rain. On the other 

 hand, the subsoil in its case becomes more disintegrated, 

 therefore more porous, more retentive of moisture in a 

 favourable condition, and more permeable by the roots. It 

 is probably in part due to this action that the effects of 

 a given amount of nitrogen as nitrate of soda increase from 

 year to year compared with those of an equivalent appli- 

 cation as ammonia-salts. How much of the greater effect of 

 the nitrate may be due to this action, and how much to the 

 mineral manure which in the first year of the experiments 

 was supplied to the nitrated plot, it is impossible to deter- 

 mine. The fact that fair crops were obtained by nitrogenous 

 manures alone throughout the entire period is a striking 

 illustration of the mineral resources of such a soil ; and it 

 shows that when in what may, in an agricultural sense, 

 be called a corn-exhausted condition, it was deficient in 

 available nitrogen relatively to available mineral con- 

 stituents. Putting together the results obtained with 

 minerals alone, and with nitrogenous manures alone, it must 

 now be apparent that the exhaustion noticed in the former 

 case was due to a deficiency of available nitrogen in the soil. 

 It is, indeed, of no little interest to know that on a somewhat 

 heavy soil, consisting of a somewhat heavy loam with a 

 clayey subsoil, and of only moderate corn-yielding capa- 



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