What is the nutrient content/or value of spent mushroom substrate?
The nutrient content varies with different sources. A typical analysis has: • Dry matter between 40-60% • pH between 6-8 • Carbon to nitrogen ratio that is generally below 30:1, which means it will give up nitrogen rather than tie up available nitrogen. A 10 ton/ac fall application typically gives 80 lb/ac of nitrogen, 105 lbs/ac of phosphorus and 175 lbs/ac of potash. The nitrogen is about the same total value as dairy manure, only more of the nitrogen is in the organic form and is more slowly released over time. Studies in vegetables in the US have shown that there is less nitrogen leaching from spent mushroom substrate than from commercial fertilizers. As for the phosphorus and potash values, they are actually higher per ton than raw dairy manure. This is not unexpected since the composting process tends to concentrate mineral nutrients. Not to be overlooked are the micro-nutrients found in spent mushroom substrate. It contains appreciable amounts of iron, manganese, zinc and boron.
