Influence of precipitated calcium carbonate (CaCO3) on shiitake (Lentinula edodes) yield and mushroom size. 
Synthetic substrate consisting of oak sawdust (50%), white millet (28%), winter rye (11%) and soft red wheat bran (11%) was non-supplemented or supplemented with 0.2%, 0.4% or 0.6% (dry weight basis) precipitated calcium carbonate (CaCO(3)).  Shiitake (Lentinula edodes) was grown in two crops to determine the effect of three CaCO(3) levels on mushroom yield and size.  Yields and biological efficiencies (averages for two crops) from substrates non-supplemented with CaCO(3) were lower by 14.1%, 18.4% and 24.9% compared to treatments supplemented with 0.2%, 0.4% and 0.6% CaCO(3), respectively.  Mushroom size (weight) was larger with non-supplemented substrate (16.8 g) compared to substrate supplemented with 0.6% CaCO(3) (15.1 g).  However, mushroom production was more consistent from crop to crop when 0.6% CaCO(3) was added to substrate.