Effect of sampling time and leaf position on leaf nutrient composition of Protea 'Pink Ice'

Abstract

Seasonal fluctuations in the concentrations of 12 nutrients were assessed over 3 years for Protea 'Pink Ice' in 3 plantings in the Mount Lofty Ranges of South Australia. Nutrient concentrations in youngest fully expanded leaves (YFEL) generally showed strong seasonal trends, reflecting seasonal vegetative and flowering patterns. During May-August and December-February, YFEL concentrations of nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), sodium (Na), sulfur (S), copper (Cu), zinc (Zn), manganese (Mn), and iron (Fe) were relatively stable, making these suitable times for sampling. The effects of sampling error and leaf position were also determined. The error associated with our sampling procedure was within acceptable limits (coefficients of variation 45%) for N, P, K, Ca, magnesium (Mg), Na, S, and boron (B). Differences in nutrient composition between YFEL and YFEL - 1, YFEL - 2, YFEL + 1, YFEL + 2, and YFEL + 3 were of little practical significance. Nutrient removal by flowering stems and concentrations of nutrients in different fractions (bloom, stem + leaves, axillary shoots) of flowering stems were determined for each site. Nutrient concentrations in flowering stems were generally lower than in leaves. Nitrogen concentrations in axillary shoots and K concentrations in blooms were significantly higher than in other fractions. For preferred sampling times, seasonal trends showed that concentrations of N, P, K, Ca, Na, S, Cu, and Fe were fairly stable over May-August. Similarly, concentrations of N, P, K, Ca, S, Zn, and Mn were relatively stable during December-February, after completion of the spring vegetative flush.