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

Abstract

Nutrient depletion and accumulation of toxic metabolites in compost are believed to be limiting factors and responsible for decreased yields as a mushroom crop ages. The objective of this study was to identify, monitor, and quantify 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 compost solution increased as the crop aged. The addition of hypnum peat and rock phosphate to compost at spawning lowered potassium and magnesium concentration in compost solution, which suggested the accumulation of potassium, and possibly, magnesium may limit later yields. Compost solution extracted from hypnum peat moss and rock phosphate supplemented compost had less phosphorus in solution than unsupplemented compost, suggesting an increase in uptake of phosphorus by the mushroom mycelium increased later break yields. Resin-extracted potassium from the saturated paste extract solutions decreased until primordia formation, then increased as the crop aged. Hypnum peat and rock phosphate added to compost at spawning lowered resin-extracted potassium and increased resin-extracted calcium after casing. Most resin-extracted cations from around the mycelium in situ increased as the crop aged. IR-120-Na resins extracted more calcium and less potassium from around the mycelium in hypnum peat supplemented compost. The results suggested that calcium or potassium interfered with the nutrient uptake of phosphorus as the crop aged, thus reducing yield.Key words: Agaricus bisporus, hypnum peat, ion exchange resins, chelation, calcium, potassium, phosphorus.