AVERAGE PRODUCE PER ACRE. 119 



(including, in the case of straw, a large amount of silica, with 

 potash and lime), is, directly or indirectly, returned to the soil 

 whence it was taken. That, however, is true with respect to 

 nearly the whole of tlie turnip crop, and also with respect to 

 the hay crop if wliolly consumed on the farm on which it is 

 jjroduced. Along with the amount of the principal constituents 

 of our common crops, it is interesting to consider and to com- 

 pare the amount of the same substances found in, say ten, 

 fifteen, or twenty tons of farm-yard manure. In order to facili- 

 tate such comparison, we have appended the amount, in pounds, 

 of nitrogen and principal ash constituents in ten tons of average 

 fairly well rotted dung. If the decimal points be removed one 

 place to the left, the numbers will, of course, represent the com- 

 position of one ton ; and from these the amount in the several 

 substances in any number of tons can readily be obtained. Dr. 

 Voelcker's admirable series of analyses forms our chief authority 

 here; but as the manure with which he dealt was made up 

 partly of the excrements of pigs, along with that of cattle and 

 horses, it seems probable that it was rather richer in nitrogen 

 and phosporic acid than the common average. In deference to 

 other authorities, it has been deemed advisable slightly to 

 modify the results obtained at Cirencester. The figures give as 

 fair an average as can be obtained of dung that has been 

 moderately well preserved for five or six autumn and winter 

 months. It is needless to say that much will depend upon 

 the nature of the food which the animals producing the dung 

 consume. If any amount of cake and corn has been used, the 

 farmyard manure will be richer in nitrogen and phosphoric 

 acid than that here represented, to the extent of at least 2 or 

 3 lbs. per ton of the former, and 1 to Ih or 2 lbs. per ton of the 

 latter. The potash, &c., will not be materially increased. The 

 average of lime (not stated in the table) is about 23 to 26 lbs. 

 per ton. On the calcareous soil at Cirencester, Dr. Voelcker 

 found the lime to be considerably above wliat seems to be the 

 average. In well-rotten dung, nearly one-half of the phosphoric 

 acid, one-half of the ammonia, of the magnesia, and of the sul- 

 phuric acid, and nearly the wliole of the potash, are in a soluble 

 condition. 



It is worthy of notice how nearly the crops that we have as- 

 sumed approach each other in the weiglit of the total air-dry 

 produce per acre. In so far as the cereal, the pulse, and the hay 

 crops are concerned, that can be seen in the following table — the 

 produce both of grain and straw being assumed to be in what is 

 called an air-dried condition. It may be worth while, and not 

 without some interest, to bring all the crops to a level in respect 

 of water, by giving the amount of the completely dry matter of 

 the grain and straw, roots and tops, of each crop per acre ; and, 



