The Use of Spent Mushroom Substrate (SMS) as an Organic Manure and Plant Substrate Component

The effect of the addition of SMS to soil on the growth of perennial ryegrass was studied in a pot experiment. SMS raised the analyzed levels of P, K, Mg and Electrical Conductivity (EC) but not the level of NO₃-N. At the first harvest, there was a positive response of growth up to a rate equivalent to 50 t/ha but above this growth declined. By the final harvest, there was a positive response of dry matter production up to the highest rate, 400 t/ha. The calculated nitrogen efficiency of dry matter production for SMS averaged 3.1 as against 21.1 for calcium ammonium nitrate. Leaching an SMS/peat column with distilled water at 10 day intervals over a 60 day period recovered 94 percent of the K in the leachate, 33 percent of the P and only 15 percent of the N. In SMS/peat mixes, early growth of tomato seedlings did not respond to rates above five percent of SMS by volume and was reduced when the SMS rate was above 20 percent. When the plants were grown on to a more mature stage, there was a response up to 20 percent SMS. In three experiments, SMS was used as a single nutrient source to supply N, P and K respectively. When used as a source of P and K, there was little benefit from increasing the rate of SMS above five percent. However, when used as a source of N, plant growth increased up to a rate of 25 percent SMS. There was no response to the addition of trace elements to SMS/peat substrates. When an SMS/peat substrate, containing five percent SMS by volume was supplemented with extra N, plant performance was as good as in a peat substrate with inorganic fertilizers.