Effect of pH and incubation temperature on nitrogen drawdown index of woodwaste potting media

Abstract The effect of pH and incubation temperature on the nitrogen (N) drawdown index (NDI) of woodwaste potting media was investigated. A sand/pinebark/sawdust medium (1:1:8) was amended with seven rates of dolomite to give seven media with pH in the range 5.3 to 6.6. Nitrogen Drawdown Indices (NDI) for the addition of 75 mg N/L (NDI75) and 150 mg N/L (NDI150) were measured for each medium after incubation at 10, 13, 20, and 30°C. NDI was unaffected by pH of the medium but was significantly influenced by incubation temperature. Nitrogen immobilisation was minimal at 10°C but increased with rising temperature such that at 30°C even the NDI150 was zero. It is suggested that NDI tests be performed under conditions similar to those in which the potting media will be used in order to accurately assess potential N immobilisation under production conditions. A significant relationship between NDI assessed as NDI75 and NDI150 is reported. The relationship indicates that potting media with NDI150>0.42 and NDI15...