Effects of spent mushroom substrate on soil chemical conditions and plant growth in an intensive horticultural system: a comparison with inorganic fertiliser

Between November 1991 and 1993, 4 consecutive vegetable crops (sweetcorn, 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, 20, 40, or 80 t/ha (moist), both with and without 1 rate of inorganic fertiliser for each crop (120-338, 40-100, 53-100, and 60-114 kg/ha, respectively, of nitrogen, phosphorus, potassium, and sulfur). SMS applications caused a rapid increase in soil inorganic N concentration, but after this it had a variable effect. There was some evidence of N immobilisation following initial SMS applications of 20 t/ha. SMS applications increased both soil pH and CEC, whereas inorganic fertiliser decreased both. Sweetcorn and cabbage yields were increased by SMS when inorganic fertiliser was not used, and potato yield was increased irrespective 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 additional N with SMS.