EFFECT OF BASAL AND SIDE-DRESSED PHOSPHORUS ON THE ACHENE YIELD AND PYRETHRINS CONCENTRATION IN THE ACHENES OF PYRETHRUM (TANACETUM-CINERARIIFOLIUM) AND ON SOIL AND PLANT PHOSPHORUS

Field experiments were conducted for two years on a krasnozem at Devon port and on an alluvial soil at Ouse in Tasmania to investigate the ef fect of basal and side-dressed phosphorus (P) on the yield (achene yie ld) and pyrethrins (Py) concentration in dry achenes, on tissue P conc entrations of pyrethrum and on soil Colwell P (P-c). 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 bas al P ha(-1) increased achene and Py yield by greater than or equal to 50% in the 1990 crop at both sites. Residual P from the 1990 applicati on tended to reduce the 1991 achene yield, Py concentration and Py yie ld 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 com bined 1990 and 1991 achene and Py yield was attained with 50 kg P ha(- 1) and no side-dressed P. Top-soil P-c in 1990 was highly correlated w ith rates of both basal and side-dressed P, achene yield and P concent ration in plant tissues. The concentration of P in shoots, apical tiss ues and youngest fully expanded leaves of the 1990 crop was highly cor related with the rate of basal P and achene yield. The apical tissues were more suitable for diagnostic work because of the ease and speed o f sampling.