106 The Rothamsted Barley Experiments. 



guano, containing 12 per cent, of ammonia, without super- 

 phosphate. But when rape-cake is used, rather more 

 nitrogen in that form will be required to yield a given 

 increase of the crop for which it is applied ; a given amount 

 of nitrogen costs more in rape-cake than in either sulphate 

 of ammonia or nitrate of soda. When the increase is obtained 

 by sheep-folding, or by farmyard manure, very much less will 

 be obtained in the first crop, in proportion to the nitrogen 

 contained in the manure. 



These generalisations may be compared with corresponding 

 ones, based on the continuous growth of wheat for twenty 

 years on the same land. For wheat, as for barley, the 

 quantity of increase obtained for a given amount of ammonia, 

 or its equivalent of nitrogen, in manure, varies exceedingly 

 according to the amount applied, to the provision of mineral 

 constituents within the soil, and to the seasons. But, under 

 the conditions most comparable with those of ordinary 

 practice, approximately 51b. of ammonia, or its equivalent of 

 nitrogen, were on the average required to yield one bushel 

 increase of wheat, and its proportion of straw. Now, one 

 bushel of wheat may be reckoned to weigh 611b., and its 

 average proportion of straw 1051b. Thus, whilst from 21b. to 

 2^1b. of ammonia in manure will yield 521b. of barley-grain, 

 and 631b. of straw (=1151b. total produce), it required 51b. 

 to yield 611b. of wheat-grain, and 1051b. of straw (=1661b. 

 total produce). It is clear that it required much more 

 nitrogen in manure to yield a given amount of increase of 

 produce when applied in the autumn for wheat, than when 

 in the spring for barley. 



EFFECTS OF THE UNEXHAUSTED RESIDUE OF 

 MANUEES. 



The fourth section of the report is on the effects of the 

 unexhausted residue from previous manuring upon succeeding 

 crops, on the loss of constituents by drainage, and 011 some 



