If 

 1 



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if 



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56 



1880, and is almost ideutical with the mean of those made at the latest 

 date. 



The first point to observe is that the first 9 inches of the garden 

 ground contained more than half a per cent, of nitrogen, nearly four 

 times as much as the average of the arable soils, and nearly five times 

 as much as the exhausted clover land soil. It is of course true that 

 the soil would be correspondingly rich in all other constituents ; but 

 some portions of the arable soil where clover failed, had received 

 much more of mineral constituents by manure than had been removed 

 in the crops. 



The means of the determinations made on the three separate 

 samples taken in 1879 are seen to agree very well, and the results can 

 leave no doubt that there has been a great reduction in the stock of 

 nitrogen in the surface soil. The reduction amounts to nearly 29 per 

 cent, of the total. Reckoned per acre, as shown at the foot of the 

 table, it corresponds to a loss of 2,732 pounds during the twenty-one 

 seasons of growth ; and although really good crops are still grown in 

 mo.st years, there has been, with this great reduction of the stock of 

 nitrogen in the soil, a very marked reduction in the clover-growing 

 capability of the soil. Thus, during the first fourteen of the twenty- 

 nine years of the experiment, seed was sown only three times ; whilst 

 during the last fifteen years it has been necessary to sow ten times. It 

 is obvious, therefore, that the plant stood very much longer during 

 the earlier than the later years. Then, again, the produce from the 

 three sowings during the first fourteen years was nearly twice as 

 much as has been obtained since. 



The question obviously arises — what relation does the amount of 

 nitrogen lost by the soil bear to the amount taken off in the crops ? 

 We quite admit the uncertainty of calculations of produce per acre 

 from the results obtained on a few square yards. We are, however, 

 disposed to estimate the average yield of nitrogen over the twenty-one 

 years between the two periods of soil sampling at about 200 pounds 

 per acre per annum. The table shows that against this we have an 

 estimated loss of nitrogen by the first 9 inches of soil of 130 pounds 

 per acre per annum, corresponding approximately to two-thirds of 

 the amount estimated in the crop. 



There is, however, evidence leading to the conclusion that, in the 

 case of arable soils to which excessive amounts of farm-yard manuro 

 are applied, there may be a loss by evolution as free li-^rogen ; and, 

 obviously, so far as this may have occurred in the garden soil, there 

 will be the less of the loss determined in the surface soil to be credited 

 to assimilation by the growing clover. 



