4. Compost
The white-button mushroom is grown on a select substrate which provides adequate levels of nutrients to support the crop so that it can successfully complete with other microorganisms. Traditionally, partially-decomposed horse-manure has been the principal medium for providing the required nutrients in artificial cultivation of the mushroom and it is only in recent times that other materials have also been used successfully.
(a) Materials and their functions
(i) Base materials. These includes wheat straw, maize cobs and other similar cellulosic plant wastes with or without horse-manure. Conventionally wheat straw either alone or mixed with horse-manure is the most widely used base material. When wheat straw is not available, straws of the other cereals, like rice of barely may be used. the chief function is to provide cellulose, hemicellulose and lignin in bulk. These materials also provide proper physical structure to the mixture to ensure the necessary aeration for the build up of microbial population and the subsequent spawn growth in the compost. Rice and barley straws are quite soft and decompose quickly, leaving only a little fibre for imparting a proper physical structure to the compost. Therefore the types and quantity of supplement should be discretely utilized at the proper time.
(ii) Supplements. These are for activating fermentation and can be categorised as :
Animal dungs. These include horse- and chicken-manure, the extremely variable manures in composition. Nitrogen cantent may vary from 1 to almost 5% . In addition to nutrients, they contribute greatly to the final bulk density of the compost. cow manure is not considered suitable.
Carbohydrate nutrients. From molasses, wet brewers' grain and malt sprouts, carbohydrates are readily available.
Concentration meals. These materials are usually used for animal feeds and include wheat or rice bran, dried brewer's grain, the seed meals of cotton, soya, castor and linseed. In these, both nitrogen and carbohydrate are available rather slowly. Nitrogen content may vary from 3-12%. The oil and mineral content of some of these may be significance in mushroom nutrition.
Nitrogen fertilizers. Nitrogen in chemical fertilizers (ammonium sulphate, calcium ammonium nitrate and urea) is rapidly released for the quick growth of microbial population.
Materials to correct mineral deficiencies. These are muriate of potash and calcium superphosphate.
Materials to correct greasiness. Gypsum and calcium carbonate serve to precipitate suspended colloidal materials and neutralize greasiness.
The choice of materials within each category is largely determined by cost-factors and their availability locally. Compost prepared from horse-dung mixed with straw are termed as 'natural', whereas they are called synthetic if the base material is used is mainly straw without bulk animal-manure.

(b)Wheat straw
Straw protected from rain is preferred. One year old straw which is no longer bright yellow and shiny, can be used only if it is tough. Full-length straw must be chopped to smaller size, about 8-10cm length, or else the heap would be less compact. Such a heap would not be able to retain moisture and termentation would be slower. The reverse, if the straw is too short, the heap would be compact and with very little air space inside allowing anaerobic fermentation. Straw, as is sold in the market for cattle feed is quite suitable. Composting is a microbial process requiring biological changes in all parts of the straw tissues and for this, it is essential that the straw tissue be accessible to the appropriate bacteria and fungal enzymes. Microbial action starts as soon as the straw is wetted and stacked in a heap. If the straw is short, fragile and damp, all parts of it will become exposed to microorganisms in a short time ans composting will start early and proceed fairly uniformly. If the straw is long, tough and dry, cut ends and few broken points may start microbial activity, leaving other parts untouched until later, to result in uneven composting. To include speed and uniformly, it needs much more mechanical breakage and wetting treatment at the beginning of the preparation.
Horse-manure
Stable manure with wheat, barley and hay-bedding must be collected regularly from the stables at intervals not more than a fortnight. Manure that has been collected over a long period of time will not ferment properly. It should be an even mixture of droppings and straw well-soaked in urine. Care should be taken that there is no admixture of manure of other animals, garbage or other trash. There should not be excess water because very wet manure cannot be stored satisfactory.

Composting theory
Composting for mushroom cultivation has 3 basic purposes :
(i) it transforms the horse-manure and straw into the substrate more suitable for the growth of Agaricus bisporus mycelium than for the many microorganisms whose presence in such a substratum cannot be avoided;
(ii) to create a favourable medium for the unfavourable microbial flora which does not inhibit the growth of A. bisporus. Protein in the countless dead bacteria and other microorganisms is a vital item in mushroom nutrition; and
(iii) its fermentation temperature is high enough to eliminate most harmful pests and diseases.
Composting is accomplished by pilling up wetted inputs in the heap. When this is done properly the temperature inside the heap begins to rise due to the aerobic fermentation brought about by bacteria and other microorganisms. It is not unusual to reach a temperature of 70⁰-74⁰C, in the center of the heap on the third of composting. Because of the high temperatures which build up in composting heaps, thermophillic and the thermotolerant organisms quickly dominate over the mesophiles. In the early stages, the natural mesophile flora subside but the population of the thermophiles and thermotolerants increases. Bacterial population dominates and their rapid increase in numbers coincides with maximum heat generation--consequently, the temperature build up. This is followed by a relatively prolonged stage dominated by thermophiles mainly thermophilic actinomycetes. As the fermenting organisms require both water and oxygen, the heap is watered frequently and aerated by 'turning'. If there is unsufficient moisture, the microorganisms require cannot function properly. If there is an excess of moisture much oxygen is excluded and anaerobic fermentation sets in resulting in a soggy and stinking compost. In such a compost mushroom spawn will not grow.
During composting, ammonia gas is liberated and some of it is lost to atmosphere, but some is consumed by bacteria to produce nitrogenous intermediates which are eventually converted into protein by another kind of bacteria. Composting more than necessary results in loss of valuable nitrogen and cellulose.