2^4 FARMYARD MANURE [chap. 



unused fertilisers as if they were contained in bags still 

 unopened from the manufacturer. We have seen in the 

 analysis that the manure made from rich feeding stuffs 

 is very superior to that made from low-grade materials 

 like roots and hay alone. From the records of the 

 experiments upon fattening animals, we can obtain 

 some idea of how much nitrogen contained in the food 

 eventually reaches the soil. We have seen, for example, 

 that the animal only retains perhaps lo per cent of 

 that which was given to it in the food, but that in 

 making the manure, considerable losses set in even 

 under the best conditions — losses due to the volatilisation 

 of ammonia and to the setting free of nitrogen gas by 

 bacteria. Though these losses are variable, and depend 

 both upon the nature of the stock and the care taken in 

 managing the manure, we can assume as a working 

 compromise that half of the nitrogen contained in the 

 food fed to the different classes of animals upon the 

 farm will eventually reach the land again. Of the 

 nitrogen and phosphoric acid, the losses are confined 

 to the proportion retained by the animal and whatever 

 may be lost by drainage, but we may again assume 

 that about three-quarters of the phosphoric acid and all 

 of the potash contained in the food will come back to 

 the land. Acting upon these assumptions, we may 

 proceed to calculate the value of the materials which 

 the consumption of a ton of any given food-stuff will 

 add to the manure made during its consumption. To 

 take a concrete example — the decorticated cotton-seed 

 cake contains about 6-9 per cent, of nitrogen, and we 

 assume that half of this (3-45 per cent.) finds its way 

 into the manure. If, on the principle explained before, 

 we reckon that the unit, i.e. r per cent, of nitrogen, is 

 worth I2s., then the value of the nitrogen added to the 

 dung by the ton of cake will be £2, is. 6d. The cake 



