412 IOWA DEPARTMENT OF AGRICULTURE 



If it were possible to preserve all the elements in the manure and if 

 leeching and fermentation could be prevented it would be possible to 

 return the above amount of fertility to the land, but every practical 

 man knows that this is not possible under ordinary farm conditions. It 

 has been found by investigators that if a person returns 60 per cent 

 of the fertility in the manure voided by the cow, he is doing splendid 

 work. If butterfat is sold from the farm and the skim milk returned 

 for feeding, we get much of the fertility back. In the feeding of skim 

 milk there is also loss and we cannot expect to return more than 60 

 per cent of the fertility or the elements required to make the milk, 

 for there is waste in handling the skim milk. The calf or animal to 

 which it is fed takes some of the elements for growth and the fertility 

 in the manure from the animals gives up some of its fertility to leeching 

 and fermentation. If we assume that 60 per cent of the fertilizing ele- 

 ments in the manure and skim milk is returned to the land, we get the 

 following table: 



Lbs. Lbs. Lbs. 



Nitrogen Phosphorus Potash 



Fertility returned to the soil in manure 93 37 70 



Fertility returned to the soil through skim-milk 18 7 7 



Total fertility returned to the soil in ma- 

 nure and skim-mik Ill 44 77 



In the following table we show the amount of fertility used in the 

 manufacture of 8,000 pounds of 3.8 per cent milk and the amount that we 

 may reasonably expect to return to the soil and the loss. 



Lbs. Lbs. Lbs. 



Nitrogen Phosphorus Potash 



Fertility used 207 82 < 156 



Returned to soil in manure if skim-milk is fed 111 44 77 



By subtracting we get a total loss of . ... 96 3S 79 



If the skim-milk is not returned to the farm 

 we get an additional loss of 12 5 5 



Added to the other loss we get 108 43 84 



showing the total loss in fertility of the farm for each cow that will pro- 

 duce 8,000 pounds of 3.8 per cent milk per year. 



If we had to go in the market and purchase these elements at commercial 

 fertilizer prices they would cost in the neighborhood of $22.00 but fort- 

 unately for the dairyman, the nitrogen which costs 15 cents a pound in 

 the market can be obtained from the air free and there is an unlimited 

 supply. It becomes necessary, however, for him to grow some form of 

 legumes such as clover or alfalfa or cowpeas for gathering this nitrogen 

 from the air. This is no hardship, for every well regulated dairy farm 

 should have a good supply of either clover or alfalfa or cow pea hay on 

 hand. It is therefore safe to state that the farmer who practices the sys- 

 tem of rotation and feeds legume hay, need pay no attention to the nitro- 

 gen supply of his farm. 



