in the case of 8a an average increase of 128 lb. of total produce, allowing 

 in every case for the original difference between the two halves of the 

 plots. The influence of the straw in diminishing the effect of the am- 

 monium salts is thus altogether doubtful. 



In the experiments on permanent grass, the addition of 2,0001b. of 

 cut wheat straw to a complete manuring with ash constituents and am- 

 monium salts has apparently increased the annual produce of hay by 7 j 

 cwt. on an average of forty years, 1856-95. In this experiment the 

 straw is applied to the land- in January, and the ammonium salts in 

 February and March. 



The results furnished by the field experiments at Rothamsted, both 

 with farmyard manure and straw, do not thus substantiate the conclu- 

 sions of the German experimenters ; the results obtained by the latter 

 were due to the special conditions of their experiments, and especially 

 to the large quantities of dung or straw which they employed. 



Apart from the subject of denitrification, there are many facts of 

 great practical valae which are taught by the German experiments we 

 have had under consideration. Persons unfamiliar with the method of 

 pot experiments are apt to disregard the results obtained in this way ; it 

 is foolish to do so. Pot-culture, with the opportunity it gives of main- 

 taining exact experimental conditions, is, indeed, the only trustworthy 

 method for the solution of many questions. 



One fact which comes into great prominence in the German experi" 

 ments is that ordinary farmyard manure is valueless as food for plants 

 until it is nitrified ; this is surely the only conclusion we can draw from 

 the want of action of the manure when applied in large quantities in the 

 pot experiments. In the light of these results the economy of large 

 dressings of farmyard manure becomes very questionable. 



The conditions most suitable for the nitrification of considerable 

 masses of organic matter deserve attention. Deherain's few experiraentg- 

 on the subject are very suggestive. He mixed 100 parts of ordinary dry 

 soil with 5, 10, 15, 20 and 25 parts of water ; placed these mixtures in 

 a saturated atmosphere, so as to preserve unchanged the proportion of 

 water added ; and at the end of ninety days determined the quantity of 

 nitric acid produced. A similar experiment was made with soil with 

 which 2 per cent of farmyard manure had been mixed. The results- 

 found were as under : — 



Nitric icid formed per million of soil. 



1 



Water added to 100 soil, j Natural Soil. Soil with Farmyard 



Manure. 



250 270 



10 260 360 



16 270 490 



20 290 290 



25 380 220 



