The Effects of Land Spreading and Soil Incorporation of Spent Mushroom Compost on County Monaghan Grassland Soils

Of the 280,000 t of spent mushroom compost (SMC) produced annually in Ireland, 27% is produced in Co. Monaghan and 72% of this is spread on land. On account of the serious levels of environmental pollution which exist in Monaghan, a study was carried out to investigate the effects of surface spreading and incorporation into the soil of SMC on soil properties and grass growth. In Experiment 1, SMC was applied in spring at rates of 0, 16.5 and 49.5 t/ha to small plots of permanent grassland in Co. Monaghan. Three ages of SMC were used (fresh, aged outdoors for 6 months, and aged outdoors for 12 months) in a fully randomised factorial design with 10 replications of each application rate/age combination (90 plots). Herbage dry matter (DM) production was measured over the growing season, at the end of which soil was removed from all plots for physical and chemical analysis. In Experiment 2, SMC of the three ages used in Experiment 1 was incorporated in pots with surface soil from three areas of contrasting soil type and land use in Co. Monaghan at a rate of 49.5 t/ha. There was also an untreated control in a fully randomised factorial design with six replications of each age/soil combination (72 pots). Pots were sown with perennial ryegrass and, after an 8-month period, herbage DM production was measured and selected soil chemical parameters were evaluated. In Experiment 1, application of SMC led to increased (P < 0.05) levels of plant-available soil phosphorus, potassium and magnesium, soil pH and herbage DM production but did not affect plant-available soil calcium, percent organic carbon, electrical conductivity (EC), root mass in the upper 10 cm, bulk density or percent water-stable aggregates. Age of SMC had no effect on any of the variables measured. In Experiment 2, SMC amendment affected (P < 0.05) plant-available soil phosphorus, pH, EC, and herbage DM production. Interaction effects suggested that application of well-aged SMC may give rise to unacceptably high plant-available soil phosphorus levels on high-pH soils and susceptibility to drought on sandy soils.