John M. Smagula

Diammonium Phosphate Application Date Affects Vaccinium angustifolium Ait. Nutrient Uptake and Yield

SUMMARY A commercial lowbush blueberry field with a Colton sandy soil characteristic of the blueberry barrens of Washington County, Maine was the site for this study. Diammonium phosphate (DAP, 18-46-0) was applied at 448 kg/ha on 17 May (preemergent), 31 May, 14 June, 28 June, or 12 July 2000 for comparison with an unfertilized control plot. Stem height was measured on 20 tagged stems in each control plot of blocks 1, 2, and 3 at the time of fertilizer application. Composite leaf tissue samples taken for nutrient analysis indicated that there was a positive linear and quadratic relationship between leaf N concentration and fertilizer application date. Leaf P concentration had a quadratic relationship with application date. Applying fertilizer on 14 June resulted in the greatest uptake of N and P as indicated by leaf nutrient concentrations. Soil samples taken at the time of leaf sampling indicated no effect of any fertilizer application on soil P concentration. Fertilizer application did not affect stem density, stem height, or number of branches. Branch length was increased only by the 17 May preemergent application of DAP. Flower bud density was increased by fertilization on 17 May, 31 May, 14 June, or 28 June, compared to the control. Yield was increased by fertilizing with DAP applied preemergent (May 17) or on May 31 but not at the later dates. This quadratic relationship was significant at the 0.1% level. Apparently, N and P from DAP accumulated to high levels in leaf tissue when applied on 14 June but there was inadequate time to influence flower formation in flower buds.

Organic Lowbush Blueberry Research and Extension in Maine

A six-year organic systems research project was conducted in Maine from 2004 to 2009. The project had several components: (1) a large replicated interdisciplinary multifactor (fertility, weed, insect, and pathogen) experiment over three cropping cycles (6 years), (2) single disciplinary experiments designed to develop organic management tools for pest management, (3) an economic analysis of current organic production, (4) a survey of organic growers for the purpose of deriving a descriptive profile and the development of grower case studies, and (5) organic Extension workshops and field meetings and production of an organic wild blueberry growers guide. This article highlights some of the outcomes of this project including: ecological interactions among pests and fertility, novel management tactics, niche-market diversity, and economic viability.

Comparison of Split or Single Application of Gypsum for Wild Lowbush Blueberry (Vaccinium angustifolium Ait.)

Gypsum (CaSO4·2H2O) was evaluated as a single pre-emergent application (4,482 kg/ha) or a split application (2,242 kg/ha pre-emergent and 2,242 kg/ha 2 weeks later) for its effect on soil nutrient release, nutrient uptake, and plant growth at two commercial lowbush blueberry fields (Clary Hill and Marshville, Maine). Gypsum applications were compared to diammonium phosphate (448 kg/ha) and a control using 0.9 m × 15 m plots arranged in a randomized complete block design with six blocks. Composite leaf and soil samples were collected within each treatment plot in July 2009 and analyzed for nutrient concentrations. Within each treatment plot, stems from four randomly placed 0.023 m2 quadrats were collected in October 2009 for stem length, branching, and flower bud measurements. Gypsum raised soil Ca and S concentrations at both fields compared to diammonium phosphate and the control. One of the fields (Marshville) was deficient in leaf N and P. Diammonium phosphate raised leaf N and P concentrations compared to the controls at both fields; but gypsum (single or split application) raised leaf N and P only at the deficient Marshville field. Diammonium phosphate increased stem branching, number of branches, length of branched stems, and average stem length at both fields. Gypsum treatments did not affect stem characteristics at either field except for stem branching, which was raised by the split application at the deficient Marshville field. Blueberry yield was increased by diammonium phosphate at Clary Hill and Marshville by 57 and 117%, respectively, compared to the control. Neither of the gypsum treatments increased yield. A split application of gypsum was not more effective than a single application.

Gypsum Rate Evaluation for Wild Lowbush Blueberry (Vaccinium angustifolium Ait.) Soils

Four rates of gypsum (CaSO4·2H2O) were compared at two commercial wild lowbush blueberry fields (Addison and Belfast, ME) to determine the most suitable rate for increasing blueberry nutrient uptake under Maine soil conditions. Gypsum treatments (1,121, 2,242, 3,363, or 4,484 kg·ha−1) were compared to diammonium phosphate (DAP; 448 kg·ha−1) and a control. Gypsum and diammonium phosphate were applied pre-emergent in May 2009 to 0.9 m × 15 m plots arranged in a randomized complete block design with six blocks in each field. Composite leaf and soil samples were collected in July 2009 and analyzed for nutrient concentrations. Within each treatment plot, stems from four randomly placed 0.023 m2 quadrats were collected in October 2009 for stem length, branching, and flower bud measurements. Soil Ca and S concentrations were increased by gypsum at both fields. Gypsum increased leaf N and P concentrations only at the field that was deficient in these nutrients (Addison). Diammonium phosphate increased leaf N and P concentrations compared to the controls at both fields. Gypsum at 2,242 kg·ha−1 or higher corrected P deficiency; but only the 3,363 kg·ha−1 and 4,484 kg·ha−1 rates corrected leaf N deficiency. At Belfast, diammonium phosphate did not increase flower bud density or yield. At the deficient Addison field, a lower rate of gypsum (3,363 kg·ha−1) than that recommended for Canadian soils (4,000 kg/ha) was effective in correcting leaf N and P deficiency. Flower bud density and yield were raised by diammonium phosphate but not by any of the gypsum treatments.

Assessment of pre-harvest treatments on Maine wild blueberry fruit shelf-life and processing quality.

Abstract To assess the impact on berry quality, four treatments were applied to six different clones of Maine wild blueberries during the 1998 field season. Three treatments; 1% calcium chloride, 1% acetic acid, and 1000 μM of methyl jasmonate and the water control were sprayed on the 1 m2 plots twice at one-week intervals. One week after the second spray the blueberries were harvested. Samples were stored at about 4°C for four weeks to determine quality. Firmness, anthocyanin leakage, and microbial counts were measured as fruit quality indicators. Field inspection showed that the calcium chloride treatments turned the leaves a reddish color. All treated plots exhibited the effects of plant stress. There were no significant effects of any treatment on fruit quality (firmness, anthocyanin leakage, or microbial assays) observed. The trend in firmness was for higher values during longer shelf-life. Antho-cyanin leakage increased during shelf-life. Microbial counts increased and then leveled off during shelf-life, exhibiting a normal pattern of media competition. Considerable variation among selected wild clones might have masked other measurable effects.