Yield responses of mulla mulla (Ptilotus exaltatus Nees.) seedlings to additions of nitrogen, potassium and phosphorus fertiliser

Native plants are increasingly being grown in Western Australia to produce flowers for export and the nutritional requirement of some of these species is not known. The nitrogen, phosphorus and potassium requirements for opti mum growth of seedlings of one such species, Ptilotus exaltatus Nees., were measured in the glasshouse experiment reported here. There was a significant (P<0.05) growth response to nitrogen fertilisers ov er the range 20-80 mg N/kg soil. At all amounts of phosphorus and potassium , except for the nil-phosphorus treatments, the largest amount of applied n itrogen (80 mg N/kg soil) gave the maximum dry weight of shoots. The dry we ight of shoots increased with the addition of phosphorus fertiliser up to 4 0 mg P/kg soil, particularly with 60 mg potassium and 80 mg N/kg soil. The addition of 160 mg P/kg soil and 120 mg K/kg soil depressed shoot growth at 80 mg N/kg soil. Potassium fertiliser increased plant growth at amounts up to about 60 mg K/kg soil. At the seedling stage of growth, critical concentration in shoots for defic iency was about 1.5% for potassium, and 0.9% for phosphorus. Adequate conce ntrations in shoots were about 1.7-2.7% for potassium, and 1.0-1.6% for pho sphorus.