CH. x] Losses from Manure Heaps 175 



These changes so far as they go seem to be entirely 

 beneficial and involve no loss, but rather a gain, in 

 value. 



Further changes arise when the heap is exposed to the 

 action of the weather. The rain soaking in encourages 

 reactions that cause evolution of nitrogen : thus it brings 

 about considerable loss. Some of the soluble substances 

 are washed out forming a black liquid which, while it 

 contains part of the fertilising substances, by no means 

 represents the whole of the loss sustained bj' the 

 heap. 



Thus the changes are greatest in heaps to which air is 

 admitted : they are least when air is excluded. The losses 

 vary in the same way. They are least when air is ex- 

 cluded and the heap is sheltered from the ram, i.e. in 

 anaerobic conditions, in a compact heap stored under 

 cover, or, what comes to the same thing, in manure 

 made in a box and kept under the animal. They be- 

 come greatest amounting to 40 per cent, or more 

 when the manure is made in open yards and then loosely 

 packed into heaps and exposed to rain in the open. In 

 the Rothamsted experiments the losses on storage for 

 three months were : 



Compact heap under cover: 4 per cent, of nitrogen. 

 Loose heap under cover : 7 ,, ., 



Heap exposed to open : 33 



The loss fell mainly on the ammonia and amides, i.e., 

 on the easily available nitrogen. (Fig. 34.) 



On this basis a 100 ton heap of manure valued at lOs, 

 a ton would have lost over 16 worth of material in three 

 months' exposure to the weather. 



Formerly it was supposed that the loss of nitrogen 

 took place mainly as ammonia, and farmers were ad- 



