Effect of Spent Mushroom Substrate on Seed Germination of Cool-season Turfgrasses

Abstract

Spent mushroom substrate (SMS) is used by the turf industry in the northeastern United States for soil improvement. When tilled into soil at high rates, some turfgrass managers claim that SMS inhibits turf seed germination. The authors’ objectives were 1) to determine whether fresh SMS inhibits turf seed germination and, if so, which species are most adversely affected; 2) to evaluate whether any inhibition incited by SMS is the result of osmotic effects or toxicity of compounds in SMS extracts; 3) to determine whether any negative effect of SMS on germination can be eliminated by leaching the SMS-amended soil before seeding; and 4) to assess the performance of SMS on seedling emergence in the field. Germination of nine turfgrass species was evaluated in mixtures made from fresh SMS (electrical conductivity of saturated paste extract = 11.9 dS·m−1) and a loamy sand soil. Germination inhibition resulting from SMS was most pronounced in the following order: Colonial bentgrass (Agrostis capillaris L.) > sheep fescue [Festuca ovina L. ssp. hirtula (Hackel ex Travis) Wilkinson] > Kentucky bluegrass (Poa pratensis L.) > hard fescue [Festuca trachyphylla (Hackel) Krajina] > creeping bentgrass (Agrostis stolonifera L.) > chewings fescue [Festuca rubra L. sp. commutata (Thuill.) Nyman] = strong creeping red fescue (Festuca rubra L. ssp. rubra Gaud.) > slender creeping red fescue [Festuca rubra L. sp. litoralis (Meyer) Auquier] > perennial ryegrass (Lolium perenne L.). SMS had a stronger negative effect on germination rates than on final germination percentages. Germination of perennial ryegrass and Kentucky bluegrass on blotter paper moistened with SMS extracts or polyethylene glycol of equivalent osmotic potentials showed that the inhibition was primarily the result of osmotic effects. In an experiment with a 50% soil/50% SMS (v/v) mixture, Kentucky bluegrass germinated better in pots that had been watered with 133% or 167% of the evaporation rate for 10 days prior to seeding than in unleached pots. Although the negative effect of SMS on seed germination was not confirmed in a field study in which ECe values never exceeded 4.1 dS·m−1, the authors conclude that incorporation of high rates of SMS represents a potential problem for turfgrass establishment.