14 



with the two substances referred to, in the proportion of approximately 

 three parts per 100 of dung. On the average the dung was turned 

 every ten days. At the end of ten weeks samples of dung were drawn 

 from the various pits, and a given quantity used to denitrify a definite 

 amount of nitrate of soda. On the average the dung that had been 

 mixed with nothing took sixty-three days to effect complete denitrifica- 

 tion, whereas those samples which had been treated with superphos- 

 phate and kainit effected complete denitrification in forty-one days 

 and thirty-seven days respectively. On September 13th, after 

 the dung had been in the pits for a hundred and twelve days, samples 

 were drawn, and their denitrifying power tested on nitrate of soda for 

 fifty-six days, at the end of which time the dung which had received 

 nothing had reduced $ per cent, of the nitrate, whereas the percentage 

 reduction with the samples treated with superphosphate and kainit was 

 40 and 66 respectively. 



In another series of experiments, where the dung was not turned it 

 was found that «amples taken at the end of a storage of eleven months 

 denitrified as follows : — 



Dung without any addition completely denitrified in 31 days. 

 „ with addition of superphosphate completely denitiified in 

 22 days. 



„ with addition of kainit completely denitrified in 20 days. 



Many other experiments could be quoted to show that when soluble 

 phosphates or kainit are added to dung to the extent of 3 per cent. — and 

 this is exactly the proportion in which a farmer mixes an artificial man- 

 ure with dung when he applies 6 cwt. of the former along with 10 tons 

 of the latter — the denitrifying power of the dung is intensified, and also 

 longer maintained. The result is that the amide, ammoniacal, and 

 nitric-nitrogen in the dung itself is more completely dissipated; and the 

 same is also true with regard to the active forms of nitrogen naturally 

 present in the soil with which the dung, or the ferments that it intro- 

 duces to the land, may come into contact. 



It seems to me that this explains why, when experimenting with 12 

 tons of dung per acre, we found that in 1893 the average crop of swedes 

 on nine farms in Northumberland was 2 cwt. per acre heavier with 2£ 

 cwt. of superphosphate than when we used 5 cwt. of that substance as a 

 supplement to the dung. In 1894, on eleven farms in Durham, we ob- 

 tained an average crop of swedes which was greater by 14 cwt. per acre 

 when the smaller dressing of the same substance was similarly used. 

 In 1895, on the average of nine farms in Cumberland, Durham and 

 Northumberland, the crop of swedes was £ cwt. per acre heavier by the 

 use of 5 cwt. as compared with 7 J cwt. of superphosphate ; and in the 

 same year on the same farms, 2£ cwt. of dissolved bones produced a crop 

 that was 4 cwt. per acre heavier than that grown by a double quantity 

 of the same manure. In all these cases the artificial manures were used 

 with equal dressings of farmyard manure and it is only under such con- 

 ditions that they have produced these anomalous results. 



The German investigators whose work we have had under review 

 have not offered any explanation of the prolongation of the denitrifying 



