Nitrogen in Different States of Combination. 51 



a period of thirty-two years, a total produce, grain and 

 straw, of 68321b. per acre, or 11431b. more than that 

 obtained by the farmyard manure on plot 2. Hence, it is 

 concluded, the amount of non-nitrogenous (chiefly carbona- 

 ceous) organic matter in the crop bears no relation to that 

 supplied in the manure ; the atmosphere, and not the soil, is 

 the source of this supply. 



In the two years 1863 and 1864 the farmyard manure 

 applied to plot 2 was estimated to furnish 4001b. of nitrogen, 

 and the total produce was 13,6531b. ; whilst that of plot 16, 

 which received only 3441b. of nitrogen, in ammonia- salts, was 

 19,8731b. There were, therefore, in the two years, 62201b. 

 excess of crop on the artificially manured plot. The nitrogen, 

 then, of farmyard manure and that of ammonia- salts, or of 

 nitrate of soda, must obviously be in different states of 

 chemical combination. This indeed is so, for in the dung the 

 nitrogen is mostly combined with carbon, in which form it is 

 both insoluble and inactive, and, for most crops, at any rate, 

 it only becomes available when, by the process of nitrification, 

 it ceases to be in combination with carbon, and passes into 

 the form of a soluble nitrate. Nitrate of soda contains 

 nitrogen in this form, and this is the reason it is so imme- 

 diately available to a growing crop, and becomes speedily lost 

 in the drainage water if there is not a growing crop ready to 

 make use of it. The time required for the nitrification of 

 different portions of farmyard manure will be very variable ; 

 the carbon may be separated from the nitrogen in urine in a 

 very short time, whilst it may take many years to nitrify 

 portions of the nitrogenous organic matter of straw, espe- 

 cially on heavy land. Since it requires a considerably larger 

 application of nitrogen in the form of farmyard manure to 

 grow the same amount of crop as that produced by a much 

 smaller application of nitrogen in the more active form of 

 ammonia- salts, or nitrates, it follows that in the soil where 

 dung has been employed there ought to be found a larger 

 amount both of carbon and of nitrogen than in the soil where 



E 2 



