MUSHROOM GROWING IN THE UNITED STATES 17 



It is advisable to make the straw-compost heap at least twice as high as 

 ordinary mushroom-compost heaps because of much greater shrinkage in the 

 straw heap during composting. 



The air spaces between the straw in a freshly made pile must be reduced to a 

 size similar to that of the air spaces in horse manure in order to avoid excessive 

 loss of water and heat. This can be done by adding soil or other material to 

 take the place of the droppings, by weighting down the heap, or by chopping 

 up the straw. 



Several nitrogenous fertilizers are suitable ; some of the most promising are 

 dried blood, calurea, and cyanamid. 



The minimum amount of nitrogen fertilizer necessary to obtain a satisfactory 

 compost has not been determined, but any of the foregoing materials will 

 make a fair compost if supplied at the rate of about 10 to 20 pounds of nitrogen 

 per ton of dry straw. 



When the useful mineral elements in straw are compared with those found 

 in stable manure there appears to be a shortage of phosphorus and calcium, but 

 care must be taken in adding these materials not to upset the reaction of com- 

 post. 



If an acid material such as ammonium sulphate is added to the heap it 

 should be neutralized. This is usually done by adding lime. 



Figure 10. — Mushrooms on an experimental bed of artificial manure (made by com- 

 posting 1 ton of straw with 100 pounds of dried blood and 50 pounds of calurea) 



The fertilizers should be well scattered throughout the heap and the com- 

 post wet down and handled in the same way as mushroom compost. To prevent 

 leaching, it is a good plan to wet the straw before adding the fertilizer. 



Results obtained from preliminary experiments suggest that artificial compost 

 is suitable to be made up into beds when slightly less decomposed and drier than 

 properly composted horse manure. For the present the experimenter may ex- 

 pect more work and fewer mushrooms with artificial compost than with 

 ordinary stable-manure compost. 



The question whether horse manure can be improved for mushroom 

 culture by adding such materials as ground limestone, commercial 

 fertilizers, or peat muck, often arises. Theoretically these mate- 

 rials might be of value in increasing the alkaline reserve of the 

 manure, supplying minerals or organic material of nutritional value 

 to the mushroom, or improving the physical condition of the heap. 

 In France favorable results from adding Thomas slag to manure are 

 reported ; while in the United States benefits from adding cottonseed 

 meal have been reported, a few growers add ammonium sulphate to 

 the manure, some add limestone or gypsum, and others peat muck. 

 But so far as the writer can ascertain these practices are based on 

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