World J Microbiol Biotechnol (2007) 23:1289–1296Three crops of Agaricus bisporus were grown on non-composted substrate (NCS), spent mushroom compost (SMC), a 50/50 mixture of NSC/SMC, or pasteurized Phase II compost. NCS consisted of oak sawdust (28% oven dry wt), millet (29%), rye (8%), peat (8%), ground alfalfa (4%), ground soybean (4%), wheat bran (9%) and CaCO3 (10%). Substrates were nonsupplemented or supplemented with Target (a commercial delayed release nutrient for mushroom culture) or soybean meal at spawning or casing, or with Micromax (a mixture of nine micronutrients) at spawning. Mushroom yield (27.2 kg/m2) was greatest on a 50/50 mixture of NCS/SMC supplemented with 10% (dry wt) Target at casing. The same substrate supplemented with Target at spawning yielded 20.1 kg/m2. By comparison, mushroom yield on Phase II compost supplemented at casing or at spawning with Target was 21.6 kg/m2 and 20.6 kg/m2, respectively. On NCS amended with 0.74% or 0.9% Micromax at spawning, yields increased by 51.8% (12.9 kg/m2) and 71.8% (14.6 kg/m2), respectively, over non-amended NCS (8.5 kg/m2). Conversely, mushroom yields were not affected when Micromax was added to a 50/50 mixture of NCS/SMC. Mushroom solids content was higher in mushrooms harvested from NCS amended with 0.74% Micromax (9.6%) compared to non-amended NCS (8.3%).