Relationships between soil physico-chemical, chemical and biological properties in a soil amended with spent mushroom substrate

The effects of two different spent mushroom substrates on soil physico-chemical, chemical and biological properties were studied in a plot experiment with a horticultural crop (Lactuca sativa L. var. linus). Two organic treatments were applied: spent mushroom substrate from Agaricus bisporus crop (T1) and a mixture of spent mushroom substrate from A. bisporus crop and spent mushroom substrate from Pleurotus crop (50% (v/v)) (T2), both treatments providing 100 kg ha− 1 of nitrogen. The unamended soil was used as control treatment (C). pH, electrical conductivity (EC), oxidisable organic C (oxidisable OC), available P, organic N, NH4+-N, NO3−-N, N loss, soil respiration and enzymatic activities (catalase, urease and phosphatase) were measured during 126 days after spent mushroom substrate addition to the soil. The organic amendment, particularly T1 treatment, increased the oxidisable OC, organic N and available P content of the soil. The application of spent mushroom substrates did not produce great changes on soil physico-chemical properties (pH and EC) with respect to the control soil. Organic N content in the amended soils increased at the beginning of the experiment, coinciding with the period in which N losses were positive (N gain). In all soils, NH4+-N concentration increased throughout the first two weeks of experiment and then these parameters decreased to the end of the experiment. However, the evolution of the NO3−-N content tended to decrease in all soils throughout the experiment, in the amended soil observing an initial nitrification inhibition. Finally, the addition of spent mushroom substrates increased soil respiration rate and phosphatase activity, not producing great differences in catalase and urease activities with the incorporation of these wastes into soil.