490 Oil the Growth of Barley hj different Maimres, ^r. 



constantly open to a lart^er area for the collection of nutriment, at 

 each period of progression, than in the case oi tlie ammoniacal 

 salts. 



A mere glance at the comparable experiments in the Series o 

 and 4, shows how very small, especially in corn, was the increase 

 obtained by the addition of a second 50 lbs. of ammonia, or its 

 equivalent of nitrogen. In fact, its effect is in every instance 

 much less than, and on the average only about half as great as, 

 that of the first 50 lbs. This point we shall presently further 

 illustrate by the aid of analysis. But the general fact should be 

 clearly borne in mind in drawing comparisons among the indi- 

 vidual experiments. 



Going to actual figures, it is not a little remarkable that, 

 as before alluded to, approximately equal amounts of nitrogen, 

 indiscriminately in nitrate of soda, in ammoniacal salts, and in 

 rape-cake, should over a period of five or six years, give us an 

 average annual yield of corn so nearly identical. Thus the nitrate 

 gave an average annual increase of 1081 lbs., the ammoniacal salts 

 1018 lbs., and the rape-cake 1079 lbs. corn. The nitrate and the 

 rape-cake thus gave an average difference of only 2 lbs. per acre per 

 annum of corn ; the ammoniacal salts yielding about 60 lbs. less 

 than either. In straw, the nitrate and rape-cake gave respectively 

 an annual increase of 1772 and 1788 lbs., or the latter (the rape- 

 cake) only IG lbs. more than the former: the ammoniacal salts 

 gave, however, about 340 to 350 ibs. less straw annually than the 

 nitrate or the I'ape-cake. It is also worthy of remark, that, whilst 

 the nitrate of soda and the rape-cake, when used alone, gave 

 respectively 1081 and 1079 lbs. annual average of corn, the rape- 

 cake with the superphosphate, as in Experiment 19, and with 

 superphosphate and mixed alkalies, as in 20, gave almost identi- 

 cally the same amounts, namely, 1088 and 1077 lbs. Again, of 

 straw, the nitrate and rape-cake alone, gave respectively 1772 and 

 1788 lbs. of annual increase, whilst the plots 19 and 20, with the 

 same amount of rape-cake and the minerals, do not give 100 lbs. 

 more — the amount being for the rape-cake and superphosphate 

 1872 lbs., and for the rape-cake, superphosphates, and mixed 

 alkalies 1877 lbs. As there is no other point so nearly in com- 

 mon with these four different combinations as their amounts of 

 nitrogen, there can be little doubt that their main or most cha- 

 racteristic effect upon the barley crop, was due to the available 

 nitrogen they respectively supplied. 



In calling attention to this very close coincidence in the result 

 from a given amount of nitrogen supplied in different forms, it 

 should at the same time be remarked, that the fact of the supply 

 being in all tiiese cases too heavy to allow of their full action and 



