Abstract:
Field experiments were conducted for two years on a krasnozem at Devonport and on an alluvial soil at Ouse in Tasmania to investigate the effect of basal and side-dressed phosphorus (P) on the yield (achene yield) and pyrethrins (Py) concentration in dry achenes, on tissue P concentrations of pyrethrum and on soil Colwell P (Pc). At both sites, 0, 50, 100, 200 and 300 kg P ha-1 was band-placed at planting (basal P) in May 1990. In September 1991, plots were subdivided and 0, 75, 150 and 200 kg P ha-1 was side-dressed. Application of up to 100 kg basal P ha-' increased achene and Py yield by > 50% in the 1990 crop at both sites. Residual P from the 1990 application tended to reduce the 1991 achene yield, Py concentration and Py yield at both sites (P = 0.09). Side-dressing of P in spring 1991 did not influenced the achene and Py yield at either site. The maximum of combined 1990 and 1991 achene and Py yield was attained with 50 kg P ha-1 and no side-dressed P. Top-soil Pc in 1990 was highly correlated with rates of both basal and side-dressed P, achene yield and P concentration in plant tissues. The concentration of P in shoots, apical tissues and youngest fully expanded leaves of the 1990 crop was highly correlated with the rate of basal P and achene yield. The apical tissues were more suitable for diagnostic work because of the ease and speed of sampling.