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 mushro om substrate (SMS) on soil physical properties and the growth of 4 con secutive vegetable crops (sweetcorn, cabbage, potato, cabbage). Treatm ents comprised 0, 20, 40, and 80 t/ha of moist SMS, both with and with out inorganic fertiliser, applied to each crop, giving a range of SMS rates up to 320 t/ha. SMS improved the environment for plant root grow th by decreasing soil bulk density (by 0.05-0.25 g/cm(3) at 100 mm dep th), increasing aggregate stability (by 13-16%), reducing clod and sur face crust formation (by 16-31 and 18-94%, respectively), increasing t he infiltration rate (by 130-207 mm/h), increasing the water content o f the soil (by 0-7% w/w), and reducing diurnal temperature changes. So me 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 relate d 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, infiltratio n rate, and aggregate size distribution. Soil physical properties had a large influence on the potato yield irrespective of fertiliser use a nd on both cabbage crop yields when fertiliser was not used, but not o n the sweetcorn yield (the first crop to be grown). The effect of chan ging soil physical properties on plant growth was most apparent when f ertiliser was not used. This was because the improved physical propert ies increased plant yield (at least in part) because of increased plan t nutrient uptake.