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- Author or Editor: David Percival x
Environmental losses of soil-applied nitrogen fertilizers were examined during 2004 in commercial wild blueberry fields in the vegetative phase of production in Nova Scotia (NS) and Prince Edward Island (PE). A randomized complete-block experimental design with five treatments, five replications, a plot size of 8 × 6 m, and 2-m buffers between plots was used. Treatments consisted of a control (no fertilizer application) and nitrogen applications (N at 35 kg·ha-1) of ammonium sulphate (AS), urea (U), diammonium phosphate (DAP), and sulfur-coated urea (SCU). Nitrogen applications occurred on 19 May and 9 June at the Kemptown (NS) and Mount Vernon (PE) sites, respectively. Cumulative ammonia volatilization was determined through the use of open top chambers with volatilization samples collected on 1, 2, 5, 8, and 12 days after treatment application. In addition, leaf tissue and yield component data were collected. A significant volatilization treatment effect was present at the Kemptown site with the U and SCU treatments having volatilization rates that were 321% and 207% greater than the control, respectively. Therefore, results from this study indicate that volatilization losses are significant and site specific and can negatively influence blueberry growth.
A 2-year study in Nova Scotia examined the effectiveness of thickly applied organic mulches as a method of weed control in highbush blueberries (Vaccinium corymbosum L.), and assessed weed and mulch impact on crop growth, leaf nutrient concentration, yield, and quality under organic production management. Mulches, applied in-row at 20-cm depth, included pine needles (PN), manure–sawdust compost (MC), and seafood waste compost (SC). Competition from weeds negatively affected crop growth and productivity, reducing canopy volume (16% to 38%), leaf nitrogen concentration and berry yields (up to 92%), number (up to 91%), and specific weight (up to 21%). Among mulches, PN proved to be the most effective in suppressing weed growth with 55% less and 73% less aboveground weed biomass compared with the control in 2005 and 2006, respectively, although PN productivity effects were much more modest. One year after application, PN lost some efficacy at suppressing weeds but was still superior to both composts. Distribution of weed species was substantially altered by mulch treatment. Both composts prevented some weed emergence (i.e., sheep sorrel), but weed seeds germinating in composts, especially SC, experienced prolific growth likely as a result of available nutrients in composts. No detrimental effects on short-term plant productivity were noted despite high C:N ratios of PN and MC (72:1 and 48:1, respectively). Plant vigor and yield were typically higher for compost mulch treatments, especially in weed-free subplots, and composts provided more complete fertilization reflected in increased leaf tissue elemental (NPK) composition. Fruit soluble solid (sugar) content was found to be significantly lower in PN and MC compared with SC, whereas total phenolic content was unaffected by mulches. Mulch application can improve organic highbush blueberry productivity by improving soil properties, nutrient availability, and weed suppression; however, precautions should be taken to avoid excess nutrient loading and weed seed contamination of mulches.
The influence of noninvasive, companion crops on lowbush blueberry production was examined at the Nova Scotia Wild Blueberry Inst. in 1998. A randomized complete-block experimental design was used with four replications and a plot size of 10 × 6 m. Treatments consisted of a control (no companion crop), sawdust, creeping red fescue, hard fescue, chewings fescue, sheeps fescue, birdsfoot trefoil (BFT), and redtop. Measurements of companion crop height, dry weight, and density, and lowbush blueberry vegetative and reproductive data were recorded. In addition, the effects of the companion crops on soil stability and weed pressures were measured at the conclusion of the growing season. Overall, the fescues and BFT established well within the blueberry canopy and in bare areas with plant densities ranging from 960 plants/m2 to 3500 plants/m2, plant dry weights of 7.2 to 11.7 mg/plant, and plant heights of 5.4 to 9.5 cm. The use of the companion crops increased yields with yields from the creeping red and hard fescue treatments being 9.0% and 13% greater, respectively, than the control. The creeping red and hard fescue treatments also significantly reduced weed pressures and increased soil stability. Therefore, using companion crops in lowbush blueberry production appears to be a viable management strategy with future research being required on herbicide use, fertility regimes, and harvestability.
Within-row weed management of highbush blueberry (Vaccinium corymbosum L.) is reliant upon herbicide applications. However, in organic production, herbicides are typically not permitted and alternative methods must be used. The impact of thick (25-cm) mulch applications on weed pressure in an organic production system was initiated at a commercial operation in Nova Scotia, Canada, during 2005. A split-plot experimental design was used with five blocks (replications), six treatments, and five plants per split plot (cv. Duke). The whole-plot factor consisted of mulch/fertility treatments and included: i) control (no amendment); ii) ammonium sulphate fertilizer (30 kg·ha-1 N); iii) pelletized poultry manure (60 kg·ha-1 N); iv) pine needles (80 t·ha-1); v) horse manure and sawdust compost (550 t·ha-1); and vi) seafood waste compost (360 t·ha-1). The split-plot factor consisted of level of hand weeding (–/+). Weed control was assessed by sampling percent ground cover and weed shoot biomass in three 0.25-m2 quadrats in nonweeded subplots. Blueberry leaf N content, plant canopy volume, and berry yield (fresh weight and number) were recorded. The manure/sawdust compost and pine needle treatments had the lowest weed biomass and percent ground cover values, thereby providing the best weed control. Weed shoot biomass, blueberry leaf N, plant canopy volume, and berry yield were greatest in the seafood waste compost treatment. Results from this preliminary study indicate the potential of using these groundcover treatments to improve organic cultural management practices.
A study examining the influence of trickle irrigation (TI), IRT-76 plastic film (PF) and straw mulch (SM) on the establishment of Rubus idaeus L. cv. `Heritage' micro-propagated raspberries was initiated at Cambridge, Ontario in 1993. Environmental, nutritional, vegetative and reproductive data were collected. Soil temperature and soil water status were greatly affected by TI, PF and SM. TI lowered soil NO3-N and increased soil NH4-N and Mg. PF increased soil NO3-N and NH4-N. Foliar N decreased by 10% with TI and increased by 8% with PF. Foliar P and Ca increased by 45 and 6% respectively, with TI. Node number was not influenced by TI, PF or SM. PF however, increased cane height, cane diameter, dry weight and leaf area by 14, 17, 77 and 11% respectively, and TI increased cane diameter by 13%. Although TI increased the number of fruiting laterals by 63%, there was no effect of TI, PF or SM on harvested berry number or weight.
Rubus idaeus L. cv. Heritage raspberries were placed in controlled environment chambers (25°C, 14-hour photoperiod, 2.0 kPa vapor pressure deficit, CO2 concentration of 380 mol·m-2·s-1) to study the effects of drought stress on leaf gas exchange and stem water potential. Whole-plant photosynthesis (Pn) and transpiration were sensitive to drought stress and gradually decreased from the second day of the study until rehydration. Stomatal aperture feed-back regulation was present during the initial 48 hours of the study with transpiration rates dropping in response to a decrease in stem water potential. Spatial differences were also present with leaf Pn, and stomatal and CO2 conductance values of the younger, distal (i.e., closer to the apex) leaves decreasing at a faster rate than the older, proximal leaves (i.e., close to crown). Evidence of increased mesophyll resistance to drought stress was apparent with ci either remaining constant or increasing, while Pn and carboxylation efficiency simultaneously decreased. Protection of the underlying photochemistry was evident with parahelionastic leaf movements which resulted in a reduction in the effective leaf area and subsequent heat load. Therefore, an optimum balance between water loss and ci existed, and an alteration in these rates represented a stomatal conductance adjustment to match the intrinsic photosynthetic capacity rather than just a causal relationship.
The influence of irradiance, CO2, and temperature on whole-plant net CO2 exchange rate (NCER) of Rubus idaeus L. `Heritage' micropropagated raspberries was examined. Within the set of environmental conditions examined, irradiation was the most important factor, accounting for 58% of the whole-plant irradiance/CO2 concentration/temperature NCER model variation, followed by CO2 concentration (28%) and temperature (2.5%). Net photosynthesis (Pn) required irradiance levels >600 μmol·m-2·s-1 PPF for saturation, greatly increased under CO2 enrichment (up to 1500 μL·L-1), and was optimum at a whole-plant temperature of 20 °C. Temperature effects were partitioned in an experiment using varying air and root-zone temperatures (15, 20, 25, 30, and 35 °C) under saturated light and ambient CO2 levels (350 μL·L-1). Air and root-zone temperature influenced Pn, with maximum rates occurring at an air × root-zone temperature of 17/25 °C. The contribution of air and root-zone temperature to the NCER model varied, with air and root-zone temperature contributing 75% and 24%, respectively, to the total model variation (R 2 = 0.96). Shoot dark respiration increased with air and root-zone temperature, and root respiration rates depended on air and root-zone temperature and shoot assimilation rate. Humidity also influenced Pn with a saturated vapor pressure deficit threshold >0.25 kPa resulting in a Pn decrease. Quantifying the physiological response of raspberries to these environmental parameters provides further support to recent findings that cool shoot/warm root conditions are optimum for raspberry plant growth.
Field experiments including supplementary trickle irrigation (IR), IRT-76 plastic film (PF), and straw mulch (STR) treatments were conducted during 1993 and 1994 to determine the influence of root-zone temperature and soil moisture status on carbon assimilation and dry mass distribution, and soil and plant nutrient content, during the establishment of Rubus idaeus L. `Heritage' primocane-fruiting raspberries. The IR, PF, and STR treatments were reapplied after the 1993 establishment year to examine their effects on an established, hedgerow planting. Physical environment, vegetative and reproductive data were collected. PF increased root and shoot mass, total flower number, and total berries harvested. Maximum leaf net photosynthetic (Pn) rates were observed under cool air temperatures and root-zone temperature of 25 °C. Field Pn measurements indicated that there was no seasonal decline in Pn. Mulch treatments however, were not beneficial to the established (i.e., 2-year-old) hedgerow planting. The root system of the 2-year-old planting was largely confined to an area within the foliage wall and also at a greater depth from the mulch treatments. Therefore, beneficial effects of mulch management on the growth and development of raspberries may be limited to the establishment year.
Leaf removal treatments were applied to Riesling during 1990 and 1991, and to Cabernet Franc and Optima in 1991. Clusters were sampled to examine the effect of berry exposure, berry contact, time of sampling, and cultivar on cuticular membrane formation and the occurrence of bunch rot (Botrytis cinerea Pers.:Fr.). Non-contact and contact cuticle proper and epicuticular wax berry samples were examined qualitatively using cryogenic scanning electron microscopy and quantitatively using enzymatic separation and chloroform extraction.
Exposed Riesling samples had 18.6% and 35.0% more epicuticular wax and cuticle proper respectively than shaded samples. Non-contact Riesling samples had 15.7% and 35% more epicuticular wax and cuticle proper than contact samples, and although significant, epicuticular wax and cuticle proper weights of Riesling increased by only 5.7% and 4.5% respectively, between veraison and harvest. Although exposed cuticular membrane samples from all 3 cultivars had more epicuticular wax and cuticle proper than shaded samples, large differences between cultivars were present. Clusters from the hand leaf removal (i.e. exposed) treatment of all 3 cultivars examined had significantly less bunch rot than clusters from the control (i.e. shaded). Cabernet Franc was the most tolerant end Optima the most susceptible of the 3 cultivars to bunch rot. Time of sampling and differences between years also influenced the occurrence of bunch rot for Riesling with less rot present at veraison compared to harvest and less rot present at the 1990 compared to the 1991 harvest. Exposure, cultivar and level of contact within the cluster are all important factors in the cuticular membrane formation process and contribute greatly to the overall susceptibility of a grape cultivar to bunch rot when grown in a temperate climate.
Manual removal of inflorescences from mature (3- and 4-year-old) American ginseng plants (Panax quinquefolium L.) at commercial timing (early July, ≈25% flowers open) increased root yield at harvest. Consecutive inflorescence removal for 2 years (third and fourth) increased yield 55.6%. Inflorescence removal in 4-year-old plants increased yield by 34.7% compared with 26.1% in 3-year-old plants. Analysis showed that the largest portion of roots (≈40%) was in the medium category (10-20 g), and inflorescence removal did not influence root size distribution. Root yield for 3-year-old plants increased quadratically with plant density, with plants lacking inflorescences having an estimated yield increase of 25%. Maximum yields of 2.4 kg·m-2 for deflowered plants were achieved at a plant density of 170 plants/m2. To maximize ginseng root yield, all plants except those needed to provide seed for future plantings should have inflorescences removed.