Effect of nitrogen, potassium and phosphorus on the yield, growth and nutrient status of ixodia daisy (Ixodia achillaeioides ssp. alata)

Abstract

The effect of annual applications of nitrogen (N), potassium (K) and phosphorus (P) on the yield, growth and nutrient status of Ixodia daisy (Ixodia achillaeioides ssp. alata) grown on a silty loam, was investigated in field experiments conducted during 1989-91 in the Mount Lofty Ranges, South Australia. The experimental design was a randomised block with 3 replications. The N and K treatments, at annual rates up to 200 kg N/ha and 150 kg K/ha, were applied as 2 equal side-dressings. The P treatments, at rates up to 200 kg/ha, were broadcast as 1 annual application. To assess plant nutrient status we sampled the fifth leaf below the growing terminal of 50 stems in October and whole stems at harvest. As rate of applied N increased, there was a significant (P<0.05) increase in total biomass harvested, number of 3040 and 41-50 cm stems, total number of marketable stems, plant height and width. Annual N application rates of 75-110 kg/ha were required for 95% of maximum biomass yield and number of marketable stems. The application of K did not significantly (P>0.05) affect yield or plant growth. First and second order interactions between N, K and year were not significant. Plant growth and yield responses to P applied as superphosphate were inconsistent and the interaction between P and year was not significant (P>0.05). Coefficients of determination (r2) for relationships between N, K and P concentrations in the fifth leaf samples v. total biomass yield and total stem number, were in the range 0.13-0.52 for the combined 1990 and 1991 data. Based on sensitivity, reproducibility and occurrence of the Piper-Steenbjerg effect, we concluded that N, K or P concentrations in the fifth leaf sampled in October, or in whole stems at harvest, were not reliable indicators of the nutrient status of Ixodia daisy. The application of N and P did not affect the concentration of minor or micronutrients in the fifth leaf. In contrast, the application of K increased calcium (Ca), magnesium (Mg) and sulfur (S) concentrations by 14.3, 33.3 and 12.2%, respectively. For a high density planting (13,000 plants) we estimated that for N, P and K, 69.4, 6.2 and 83.2 kg/ha, respectively, are removed in marketable stems. The application of P increased extractable-P concentrations in the surface (0-15 cm) soil from 22 to 73 mg/kg. We suggest that for surface (0-15 cm) soils, extractable-P and extractable-K concentrations in the ranges 15-95 and 210-260 mg/kg, respectively, are adequate and indicate that a yield response to the application of these nutrients in fertiliser may not occur.