The use of ion exchange resins to assess the changes in mineral element availability during the production of the cultivated mushroom Agaricus bisporus

Nutrient depletion and accumulation of toxic metabolites in compost are bel ieved to be limiting factors and responsible for decreased yields as a mush room crop ages. The objective of this study was to identify, monitor, and q uantify mineral element levels in composted substrate and compost solution extracts during mushroom production. Mineral element changes were assessed by placing ion exchange resin bags in compost saturated paste extracts and directly in composted substrate. The concentration of most cations in compo st solution increased as the crop aged. The addition of hypnum peat and roc k phosphate to compost at spawning lowered potassium and magnesium concentr ation in compost solution, which suggested the accumulation of potassium, a nd possibly, magnesium may limit later yields. Compost solution extracted f rom hypnum peat moss and rock phosphate supplemented compost had less phosp horus in solution than unsupplemented compost, suggesting an increase in up take of phosphorus by the mushroom mycelium increased later break yields. R esin-extracted potassium from the saturated paste extract solutions decreas ed until primordia formation, then increased as the crop aged. Hypnum pear and rock phosphate added to compost at spawning lowered resin-extracted pot assium and increased resin-extracted calcium after casing. Most resin-extra cted cations from around the mycelium in situ increased as the crop aged. I R-120-Na resins extracted more calcium and less potassium from around the m ycelium in hypnum peat supplemented compost. The results suggested that cal cium or potassium interfered with the nutrient uptake of phosphorus as the crop aged, thus reducing yield.