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15 



manure pile. One of their principal foods, the non-nitrogenous 

 material of the litter, they cannot use as food until it has been made 

 soluble by a third class of bacteria which causes the rotting of the 

 litter. Nitrates are also indispensable for their nourishment. If 

 therefore they are deprived of either one of these constituents of their 

 diet they either die or at least become harmless. 



The work of the " nitrate formers "' is beneficial ; it converts 

 organic nitrogen into nitrate, a most available form of plant 

 food. Half-rotted manure contains nitrogen largely in this form. 

 The work of " nitrate destroyers" is destructive. It removes the 

 soluble nitrates from the manure. It converts half-rotted manure 

 into well-rotted manure. In this way the different effects produced by 

 manure in the three different conditions are explained. The nitrogen 

 in fresh manure is largely organic and not immediately available. It 

 therefore has a slower and less effect than half-rotted manure. The 

 nitrogen in half-rotted manure is largely in the form of nitrates, and 

 this is available. The nitrogen in well-rotted manure has all been 

 converted into nitrate also, and was once available, but has subse- 

 quently been lost in the air. This is why the well-rotted condition 

 is the least valuable of the three. 



In handling manure the farmer should strive to place it at the dis- 

 position of the growing crop just at that moment when the most 

 nitrate has been formed and before any has been destroyed. The 

 most favorable conditions are obtained when fresh manure is packed 

 as tightly as possible, away from the air, and kept in that condition 

 till half-rotted, and then plowed under just before planting or sow- 

 ing. Under these circumstances, although the third class of bacteria 

 have in the rotting of the litter made soluble food of one kind for the 

 •nitrate destroyers," the latter have been deprived of their other 

 necessary food, the nitrates, for none could be formed in the tightly 

 packed mass and thej' have remained harmless. But the heap has be- 

 come half-rotted, even without them. After the manure is plowed in, 

 the "nitrogen formers," now having plenty of air, rapidly produce 

 nitrates which is beyond the reach of the destroyers ; for by this time 

 all their soluble noii-uitrogenous food has been decomposed and has 

 goue into the air leaving them to die. The growing plants, in the 

 meantime, absorb the nitrates. 



If fresh manure is plowed in directly before seeding, a poor result 

 is obtained, for the nitrates are not formed until after tlie plants 

 have passed their growing period, and they consequently starve. As 



