Toward Standardized Leaf Sampling for Foliar Nutrient Analysis in Breadfruit

Breadfruit (Artocarpus altilis) cultivation is gaining momentum throughout the tropics due to its high yield and nutritious fruit. One impediment to expanding production of breadfruit is the lack of agronomic research related to production management. We examined foliar nutrient concentrations of different leaf positions and leaf parts to assess within- and between-tree variance to inform an effective sampling protocol. We further validated the sampling protocol on 595 trees at 87 sites that were assessed for yield and productivity. Foliar nutrients differed significantly by categories of productivity. For the first time, breadfruit-specific standards of foliar nutrient concentrations are presented for consideration. In conclusion, we recommend that foliar sampling use petioles harvested from leaves in the third position from the branch tip using sun-exposed leaves in the midcanopy of each tree.

The influence of competition and species mixture on plantation-grown white spruce: Growth and foliar nutrient response after 20 years

A 20-year-old experimental white spruce plantation was used to identify key stand (neighbourhood competition) and soil (physical and chemical properties) factors influencing spruce growth (Periodic Basal Area Increment) and foliar nutrients. Total and species-specific competition was estimated using Hegyi’s distance-dependent index for 39 individual spruce trees. Twelve trees, covering the range of total HCI (2 to 8) and aspen competition (0% to >75%), were selected for repeated (May through October) foliar sampling. Spruce PBAI declined approximately 10% for each additional unit of total HCI; species did not significantly affect this decline. Increasing aspen presence significantly influenced spruce foliar N (1.17% to 1.31%), P (0.15% to 0.23%), and K (0.68% to 0.88%), but led to declines in Ca (0.81% to 0.48%). Multiple linear regression indicated that soil carbon (partial r2 = 0.386) and available soil moisture (partial r2 = 0.131) together explained more of the variation in spruce growth than did competition factors alone (partial r2 = 0.251). The results suggest that, at this stage of stand development, precommercial thinning operations should focus on density control and inter-tree spacing, while retaining an aspen component resulting in well-spaced, free-growing mixed stands of white spruce and aspen.

NITROGEN RATE AND TIME OF SAMPLING EFFECTS ON SOIL TEST VALUES CF HIGHBUSH BLUEBERRIES GROWN ON A MINERAL SOIL

Nitrogen rates (using urea) of 22, 67 and 135 kg/ha were applied to mature mulched and unmulched highbush blueberries over a 5 year period. Soil samples were taken each year at budbreak (prior to fertilization) and post-harvest at the suggested time of foliar sampling (approx. Aug.1) to determine N rate effects within and among years. Data analysis revealed that the most common soil test variables affected by N rate and date of sampling were pH, electrical conductivity (EC) and nitrate. For unmulched plants, a significant reduction in soil pH was found each year between budbreak and Aug. 1 for the 67 and 135 kg/ha rates, but not usually for the 22 kg/ha rate. For mulched plants, pH reduction within N rate among sample dates was usually not significant. Overall soil pH reduction was greatest for the 135 kg/ha rate over the 5 years, and the pH reduction for the 67 kg/ha rate was similar to the 135 kg/ha rate for the unmulched plants. For mulched plants, 22 and 67 kg/ha rates had a similar trend of only a slight pH reduction over the 5 years. EC and nitrate trends were very similar, with the highest levels of each on the unmulched plants.