10 



Taking the average for each eight or sixteen years of the thirty-two, 

 it is seen that in every case, even with full mineral as well as nitrogenous 

 manure, there is more or less decline in the later periods including so 

 many bad seasons; excepting on ga, where the nitrate of soda is always 

 applied in the spring. The low results or great decline, on gb, where 

 the nitrate is used alone, show the want of minerals. 



The average of the thirty-two years of mineral manure alone shows 

 an increase of only 2*^ bushels over that of the unmanured plot, though 

 during the preceding eight years it had been manured, whilst the unma- 

 nured plot had already grown eight unmanured wheat crops. The ad- 

 dition to the mineral manure of the first 43 Ibs. of nitrogen (plot 6) gives 

 an average annual increase of 8^ bushels, the second 43 Ibs. (plot 7) 

 an increase of 8^, and the third 43 Ibs. only 3^ bushels increase. This 

 result affords an illustration of the inapplicability of conclusions from 

 manure experiments, when the condition of the land is too high already, 

 or when an excess of manure is applied. A given quantity of nitrogen 

 in the form of nitrate, yielded more produce than an equal quantity in 

 the form of ammonia. The nitrate, being always applied in the spring, 

 was not subject to winter drainage. It is, however, very soluble, and 

 becomes rapidly distributed and available ; but it is, at the same time, 

 very subject to drainage after sowing, if heavy rains follow. Prior to 

 1878, the ammonium-salts were applied in the autumn, and a great loss 

 of nitrogen by winter drainage, chiefly as nitrates, was proved. To the 

 loss of nitrogen by drainage reference will be made further on. 



Thus, minerals not being deficient, the increase was in proportion to 

 the available nitrogen, when it was not applied in excess. 



It will be of interest here to call attention to the actual amounts of 

 carbon assimilated per acre per annum in wheat, and in barley, under 

 different conditions of manuring ; also to the increased amount assim- 

 ilated under the influence of nitrogenous manures. 



In Table III. are shown the estimated amounts of carbon, yielded per 

 acre per annum, in wheat over twenty years, and in barley over twenty 

 years ; each with the complex mineral manure alone, and each with the 

 same mineral manure and given quantities of nitrogen in addition, 

 supplied as ammonium-salts, or as nitrate. The gain of carbon by the 

 use of the nitrogenous manure is also given. 



TABLE III. 



Yield and gain of Carbon per acre per annum in crops at Rothamsted. 



Average Carbon per 

 acre per annum. 



Barley 20 years 1852,71. 



Complex Mineral Manure, 1138 



do do and 43 Ibs. N. as Ammonia 2088 950 



