Effect of potassium fertilization of pyrethrum (Tanacetum cinerariifolium) on yield, pyrethrins concentration in dry achenes and potassium concentration in soil and plant tissues

Pyrethrum (Tanacetum cinerariifolium), a small perennial plant, has been commercially grown for production of pyrethrins (Py) in Tasmania since 1983. Two field experiments were conducted on clay loam and sandy clay loam krasnozem soils at Harford and North Motton in the northern region and a two-year experiment on an alluvial sandy loam at Ouse in the southern region of Tasmania to study its potassium (K) requirements. Potassium, at rates up to 200 kg K ha-1, was band-placed at planting (basal K) of pyrethrum splits. At Ouse in the spring of the following year up to 100 kg K ha-1 was side-dressed in the subplots. No achene yield response was observed at Harford with the soil Colwell K (Kc) of 80 mg K kg-1 and North Motton (Kc = 132), but at Ouse (Kc = 50) in the first year a maximum increase of 86% in the achene yield was attained at 50 kg K ha-1. In the second year at Ouse, the achene yield response occurred with residual basal K up to the 200 kg ha-1 rate, where the achene yield was 3.9-fold greater than the control. In addition to the increase gained from the residual K in the second year, 50 kg side-dressed K ha-1 increased the achene yield by a maximum of 50%. Basal K did not have any effect on the Py concentration of the first year crops, but it increased the Py concentration in the second year crop at Ouse. Side-dressed K also increased the Py concentration. The Py yield at the highest rate of 200 kg basal and 25 kg side-dressed K ha-1 was more than 6.5-fold that in the control treatment. The Kc and the concentration of K in apical tissues were correlated to the rates of applied K, achene yield and Py yield, and their potential as techniques to predict pyrethrum response to K application is discussed.