EFFECTS OF SPENT MUSHROOM SUBSTRATE ON SOIL CHEMICAL CONDITIONS AND PLANT-GROWTH IN AN INTENSIVE HORTICULTURAL SYSTEM - A COMPARISON WITH INORGANIC FERTILIZER

Between November 1991 and 1993, 4 consecutive vegetable crops (sweetco rn, cabbage, potato, and cabbage) were grown in Lincoln, New Zealand. The treatments included spent mushroom substrate (SMS, a by-product of the mushroom industry) applications before each crop at rates of 0, 2 0, 40, or 80 t/ha (moist), both with and without 1 rate of inorganic f ertiliser for each crop (120-338, 40-100, 53-100, and 60-114 kg/ha, re spectively, of nitrogen, phosphorus, potassium, and sulfur). SMS appli cations caused a rapid increase in soil inorganic N concentration, but after this it had a variable effect. There was some evidence of N imm obilisation following initial SMS applications of 20 t/ha. SMS applica tions increased both soil pH and CEC, whereas inorganic fertiliser dec reased both. Sweetcorn and cabbage yields were increased by SMS when i norganic fertiliser was not used, and potato yield was increased irres pective of fertiliser use (i.e. yield increases of 38%, 82-96%, and 26 -46%, respectively, for sweetcorn cob, cabbage head, and potato tuber fresh yields). Inorganic fertiliser increased crop yields by a greater amount than SMS. A lack of soil inorganic N was the major limitation to crop growth following SMS applications, so crops may require additi onal N with SMS.