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John M. Smagula

Concentrations of nutrient elements in randomly selected soil samples taken at a 3-inch depth or the depth of the surface organic pad correlated poorly (R2= < 0.34) with leaf nutrient concentrations randomly selected from the same fields. Average leaf N concentrations in 74 of 79 fields sampled were above the 1.6% standard, while leaf P was below the 0.125% standard in 62 of the 79 fields. Leaf K, Ca, and Mg concentrations were above the standards 0.400%, 0.270%, and 0.130%, respectively in all fields. The average depth of the organic pad was 2.23 cm, ranging from 0 to 10.16 cm. Seventy five percent of the fields had organic pads 0.127-2.54 cm thick and 20% greater than 2.54 cm.

In an attempt to improve correlations, leaves within a 0.01M2 quadrat were sampled from 110 clones in 10 commercial blueberry fields and leaf nutrient concentrations compared with nutrient concentrations in 3-inch soil samples taken directly beneath the quadrat. The strongest correlation was between soil Mn and leaf Mn (r2= o.59). Leaf samples, although more expensive than soil samples, appear to be a better indicator of lowbush blueberry fertilizer requirements than soil samples.

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John M. Smagula

Liquid phosphorus (23% phosphoric acid) was applied preemergence at 0, 22.4, 44.8, 67.2, or 89.6 kg·ha-1 to 9 fields: 3 commercial blueberry fields having plants with very low (<.111%), 3 low (.111-.125%), and 3 adequate (>.125%) leaf phosphorus concentrations. Years of application ('89,'89+'91,'89 + '91 + '93) were assigned in a split-block RCB design with 4 replications at each location. A linear increase in leaf phosphorus concentration with increasing rates of P application was found in both 1989 and 1991. Differences in response were found among locations. A second application in 1991 was effective in raising leaf P levels at most locations to higher levels than the application in 1989. Also, there were higher levels of leaf P in treatment plots that only received P fertilizer in 1989 compared to controls, indicating a carry over effect.

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John M. Smagula and Ilse Fastook

Acommercial lowbush blueberry field with a history of N and P deficiency was used to study the response to several organic fertilizers. Diammonium phosphate (DAP) is the standard fertilizer for correcting N and P deficiencyin non-organic production. At a rate of 67 kg N/ha Rennaisance (8–2–6), Pro-Holly (4–6–4), Pro Grow (5–3–4), Nutri-Wave (4–1–2), or DAP (18–46–0) was applied preemergent to 1.8 × 15 m treatment plots. An unfertilized plot served as the control. Leaf N and P were deficient in the controls. DAP and Pro-Holly raised leaf N to satisfactory levels (1.6%). Only DAP raised leaf P concentrations (0.144%), compared to controls (0.122%). Leaf K was not deficient but was raised by Pro-Holly. Pro-Holly and DAP were equally effective in increasing stem height, branching, branch length, flower bud formation, and yield. Pro-Holly could effectively substitute for DAP in organic wild blueberry production.

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John M. Smagula and Scott Dunham

Flail mowing was compared to traditional pruning by oil fire over a 12-year period in two fertility experiments testing interactions with pruning method. In study one (1983–1986), urea at 0, 22.4, 44.8, 67.2, or 89.6 kg·ha–1 was applied preemergent in a split-block design with fertility as the main effect, and pruning method split within six blocks. Study two (1987–1994) continued the pruning and application of fertilizer on the treatment plots with similar rates, but diammonium phosphate (DAP) replaced urea as the fertilizer. Leaf tissue N concentrations were above the 1.6% standard and urea had no effect or decreased yield. There was no interaction of fertility and pruning and no effect of pruning method on yield. No interaction of fertility and pruning was found in study two, but DAP increased leaf P concentrations and yield and, after three cycles of mowing, yields had begun to decline in mowed plots compared to burned plots. No meaningful differences in leaf nutrient concentrations were found between plants in mowed and burned plots.

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John M. Smagula and Scott Dunham

A commercial lowbush blueberry (Vaccinium angustifolium Ait.) field deficient in leaf N and P was used to compare organic and inorganic fertilizers. In a RCB design with eight replications of 12 treatments, experimental plots received 33.6 or 67.2 kg·ha-1 rates of N (urea), P (23% phosphoric acid), N + P (DAP), N + P + K (5-10-5), or N + P + K (fish hydrolysate, 242). Fertilizer containing N alone was as effective in raising N leaf concentrations as those containing N and P. However, leaf P concentrations were raised more by fertilizer providing N and P than only P. Fish hydrolysate fertilizer was as effective as 5-10-5 in raising leaf N, P, and K concentrations in prune and crop year leaf samples. At the 67.2 kg·ha-1 rate, fish hydrolysate, N, NP and NPK increased stem length, N and NP increased flower bud density and fish hydrolysate, N and NPK increased yield compared to the control.

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John M. Smagula and David Yarborough

Experimental plots in a commercial lowbush blueberry (Vaccinium angustifolium Ait.) field deficient in N and P received preemergent 33.6 and 67.2 kg/ha rates of N (urea), P (23 % phosphoric acid), N+P (DAP), N+P+K (S-10-5) or N+P+K (fish hydrolysate, 2-4-2). A RCB design with eight replications of 12 treatments was used. Fertilizer containing N alone was as effective in raising N leaf concentrations, as those containing N and P. However, leaf phosphorus concentrations were raised more by fertilizer providing N and P than only P. Fish hydrolysate fertilizer was as effective as 5-10-5 in raising leaf N, P and K concentrations in prune and crop year leaf samples.

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Youzhi Chen and John M. Smagula

Ten clones of lowbush blueberry (Vaccinium angustifolium) having low leaf boron (B) concentrations (<20 ppm) were selected to receive fall foliar B (400 ppm), Ca (4000 ppm), B (400 ppm) + Ca (4000 ppm), or water (control). B concentration was raised in stem and bud tissue 3 months after application, but Ca concentration was unaffected. Two randomly selected 5-inch sod plugs from treatment plots within each clone were transported to cold storage at 2.7C for 1000 h to satisfy flower bud dormancy, then to a growth chamber at 24C to blossom. Pollen from plants receiving B had lower in vitro germination rates on 5% agar with 12% lactose after 20 h compared to control and Ca treatments. For in vivo germination, 10 blossoms were randomly selected on sod plugs of each treatment plot to receive 15 control-treatment pollen grains, which were allowed to germinate for 3 days. With the aid of fluorescence microscopy, a higher pollen germination percentage was observed in blossoms of plants receiving B, Ca, and B + Ca. B and Ca may have more influence on the ability of the stigma to stimulate pollen germination than on the germinability of pollen grains themselves.

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John M. Smagula and Scott Dunham

Eight commercial lowbush blueberry fields received preemergent application of diammonium phosphate at 0, 44.8, or 89.6 kg P/ha. Leaf samples taken in July of the application year showed a linear increase in P concentration with increasing DAP application. However, P concentrations in soil samples were not raised by DAP. Stem length, branching, and the number of flower buds per stem increased with DAP application. Yield, obtained by hand raking the 3 × 9-m treatment plots, increased with increasing rate of DAP. The average yield increase in response to 44.8 and 89.6 kg P/ha from DAP was 824 and 1679 kg/ha, respectively.

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Youzhi Chen and John M. Smagula

Foliar sprays of B (400 ppm), Ca (4000 ppm), B (400 ppm) + Ca (4000 ppm), or water (control) were applied in Sept. 1993 to treatment plots of 12 lowbush blueberry (Vaccinium angustifolium) clones having low leaf B concentrations (<20 ppm). Boron concentration was raised in stem and bud tissue 3 months after application, but Ca concentration was unaffected. Twenty randomly selected stems with four flower buds were tagged in each treatment plot in Apr. 1994 to determine treatment effects on fruit set and fruit characteristics. Blossoms on tagged stems were counted in late May and a count of initial fruit was taken in early July. Initial fruit set was reduced slightly by the Ca treatment, which also resulted in a lower number of flowers per bud. Tagged stems were cut before plot harvest and stored at –15C for final fruit set and fruit characteristic measurements (fruit number, diameter, weight, and firmness, and seed number and size). Treated plots were harvested and weighed in August. Boron and Ca treatments did not increase yields averaged across all clones, but some clones showed a positive response. Yield of Ca-treated plots was significantly lower than the plots without Ca treatment. Effect of treatments on final fruit set and fruit characteristics will be presented.

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John M. Smagula and M. Susan Erich.

Nutrition Surveys of commercial blueberry fields in 1987 and 1988 indicated leaf phosphorus levels were below the standard (0.125%) in most fields. To determine if phosphorus was limiting, liquid phosphorus (23% phosphoric acid) was applied preemergence at 0, 22.4, 44.8 67.2, or 88.6 kg/ha to 3 commercial blueberry fields identified in 1987 as very low (<.111%), 3 low (.111-.125%), and 3 adequate (>.125%) in leaf phosphorus. Phosphorus concentration in leaf tissue sampled in July 1989 increased linearly with increasing rates of phosphorus. Phosphorus application raised leaf phosphorus levels more in fields which had levels below 0.125%. Fields with higher phosphorus levels were also higher in leaf nitrogen, potassium, and calcium.