Mushrooms are heterotrophic organisms which require external nutrients to grow. The formula of substrate deeply influences the yield and quality of harvested mushrooms. Mushrooms require oxygen and a specific pH in order to develop a normal metabolism and to grow properly. C and N are the two main macronutrients required by fungi for structural and energy requirements; P, K and Mg are considered macronutrients for mushrooms, in addition, trace elements such as Fe, Se, Zn, Mn, Cu and Mo appear to be needed for diverse functions.
Mushroom supplementation is understood as a farming method based on the physical addition of nutritional amendments to compost, during the process of composting, the mixture of raw materials, at spawning or during casing. Supplements are most commonly applied in the different stages of mushroom cultivation, for examples at the end of the substrate preparation, prior to spawning, to promote the vegetative growth throughout the substrate; at the end of spawn run (with the substrate fully colonized by mushroom mycelium) to promote the mushroom colonization in the casing material (if required) and enhance mushroom fructification.
The use of low-cost agricultural by-products available at the productive regions is a promising approach. Among others, cereal meals and brans, chicken manure, cottonseed meal, urea, superphosphate, ammonium sulphate, grape pomace, feather flour or defatted meals from dry nuts, are recognized as active ingredients to supplement substrates employed in mushroom cultivation in Brazil or Europe. Furthermore, substrates based on grapeseed meal, defatted pistachio meal or defatted almond meal have shown similar agronomical behaviour to commercial additives for the cultivation of A. bisporus and P. ostreatus. Supplement formula consisting of 25% of soybean, black bean, wheat bran and chia showed good agronomical performance in substrates generated by self-heating pasteurization for the cultivation of A. bisporus. 25% wheat bran supplementation with saw dust may be very effective for a higher yield and 40% wheat bran supplementation for a better quality of shiitake mushroom.
In addition, adding corn husk, oat husk, soy bean nuggets and peanut shell with soya are used to generate mushrooms with higher protein content of oyster mushrooms in straw-based substrates at spawning. Other local agricultural materials have been successfully employed as supplements for the cultivation of oyster mushroom, including wood chips, boll, sugar beet pellet pulp and palm fiber along with wheat bran, rice bran, soya cake powder, soya cake powder and rice bran and carrot pulp.
In contrast, some studies show that a supplement can be too rich and increase the risk of contamination, anaerobiosis, antibiosis and subsequently lower yields. A previous study reported that no change in total mushroom yield in paddy straw mushrooms from the addition of oils of mustard, sunflower, groundnuts and cottonseed at 0.1 to 0.5. They concluded that Pleurotus species prefer non-supplemented and unfermented straw. Furthermore, another study suggests that supplements should be cautiously used because excessive bed temperature (more than 35oC) may kill the mycelium.