Analysis of fresh mushroom compost

Fresh mushroom compost is a byproduct of the edible mushroom (Agaricus bisporus) industry and represents the composted growing substrate that remains after a crop has been harvested to completion. Thirty samples were obtained from commercial mushroom farms in southeastern Pennsylvania and sent to a laboratory for analysis to determine plant nutrient content, bulk density, and particle size distribution of fresh mushroom compost. Fresh mushroom compost had an average pH of 6.6, with an average carbon:nitrogen ratio of 13:1. Organic matter content averaged 25.86% (wet weight), 146.73 lb/yard³ (wet volume) or 60.97% (dry weight). For the primary macronutrients, average total nitrogen content averaged 1.12% (wet weight), 6.40 lb/yard³ (wet volume) or 2.65% (dry weight), phosphorus measured 0.29% (wet weight), 1.67 lb/yard3 (wet volume) or 0.69% (dry weight), and potassium was 1.04% (wet weight), 5.89 lb/yard³ (wet volume) or 2.44% (dry weight). Average soluble salt content was 13.30 mmho/cm (wet weight basis). However, on a per acre basis, the calculated sodium absorption ratio of 0.38 was considered very low. The average bulk density of fresh mushroom compost was 574.73 lb/yard³ (wet volume basis), and 91% of the material measured ≤3/8 inch in diameter as determined on a wet weight basis. Overall, fresh mushroom compost is suitable as a natural organic fertilizer and soil amendment for agriculture and horticulture.