Effects of spent mushroom substrate on soil physical conditions and plant growth in an intensive horticultural system

A 2-year field trial determined the influence of applying spent mushroom substrate (SMS) on soil physical properties and the growth of 4 consecutive vegetable crops (sweetcorn, cabbage, potato, cabbage). Treatments comprised 0, 20, 40, and 80 t/ha of moist SMS, both with and without inorganic fertiliser, applied to each crop, giving a range of SMS rates up to 320 t/ha. SMS improved the environment for plant root growth by decreasing soil bulk density (by 0· 05-0·25 g/cm 3 at 100 mm depth), increasing aggregate stability (by 13-16%), reducing clod and surface crust formation (by 16-31 and 18-94%, respectively), increasing the infiltration rate (by 130-207 mm/h), increasing the water content of the soil (by 0-7% w/w), and reducing diurnal temperature changes. Some of these changes were not evident until repeated applications of 80 t/ha SMS had been made. Soil physical properties were related to crop yield, and soil physical properties’ principal components were related to crop principal components using regression analysis ( r 2 of 0·20-0·60 and 0·16-0·54, respectively). The soil physical properties that had the most influence on plant growth were specific to each crop and included bulk density, water content, surface crust cover, infiltration rate, and aggregate size distribution. Soil physical properties had a large influence on the potato yield irrespective of fertiliser use and on both cabbage crop yields when fertiliser was not used, but not on the sweetcorn yield (the first crop to be grown). The effect of changing soil physical properties on plant growth was most apparent when fertiliser was not used. This was because the improved physical properties increased plant yield (at least in part) because of increased plant nutrient uptake.