MANURIAL VALUE OF FOODS. 303 



For 100 consumed as food. 

 In live-weight increase Voided as manure. 



or milk. or in perspiration. 



Fattening sheep 3'8 96-2 



pig ... 4-0 96-0 



Milch cow ... 10-3 89'7 



Calf fed on milk 54*3 45'7 



Lawes and Gilbert" give the average manurial value per ton 

 of the common feeding stuffs as deduced from experiments, 

 assuming that they are supplied to fattening sheep and oxen. 

 The figures are based on the assumption that ammonia is worth 

 about 6d., potash about 2^d., and phosphoric acid about 3d. 

 per pound. 



The table on p. 304 is abridged and altered to suit present 

 prices from the large table given by them, and will suffice to 

 show the plan adopted in calculating the values.! 



Lawes and Gilbert in the same paper also give their estimate 

 of the unexhausted manurial value of foods used on a farm in 

 previous years. 



They conclude that with all foods, excepting hay and straw, 

 the compensation value of food used the previous year is one- 

 half the original manurial value and that the value diminishes 

 each year by one-third of its value the previous year. In the 

 case of hay and straw they state that two-thirds of its original 

 manure value should be deducted for the first year and after- 

 wards one-third from year to year. 



Consider, for example, the case where linseed cake had been 

 used for several years on a farm. The following shows the 

 compensation value of the unexhausted manure for six years, 

 assuming that the same food has been supplied yearly : 



1 ton Unseed cake. 



Original value. e k 2nd year back 3rd year back. 4th year back. 



* J.R.A.S. 1885, 600. 



t The value of nitrogen has been taken at 6d., of potash 2d., and of phosphoric 

 acid 3d. per lb. 



