March 2014
The Impact of Organic Blueberry Production Systems on Performance of Cultivars and Yield
Components (Final Report 2013-2014)
Author: Amanda J. Vance, Research Assistant, OSU NWREC;
Project Leader: Bernadine C. Strik, Professor of Horticulture, OSU;
Project Collaborator: Chad E. Finn, Berry Crops Breeder, USDA-ARS, HCRU
Objectives:



Determine the effect of cultivar and
plant age (year) on yield and fruit bud
set and fruit quality
Evaluate the long-term impact of
mulch treatment on cultivar
performance
“Describe” plant developmental stages
for cultivars and relationship to
growing degree days
Procedures:
Plants were established in October 2006 in an
organic blueberry research planting at the
NWREC. Plants were in their 7th growing
season in 2013.
Cultivars:
Duke; Liberty; Bluecrop; Bluejay; Legacy; Draper; Reka; Aurora; Ozarkblue; and Bluegold.
Soil management:
1) “Organic mulch”: incorporation: ½”-1” of compost + 2” of fir sawdust incorporated before
planting; Mulch: ½”-1” of compost topped with 3” of sawdust (replenished in Jan. 2011 and in 2013,
as needed).
2) “Weed mat”: no pre-plant incorporation; Mulch: 3” of sawdust topped with weed mat. Weed
mat was replaced Dec. 2010 with “zippered” system, but no replenishment of sawdust was
necessary (still had ~ 2 to 3 inches).
In 2007-2009, plants were fertilized with 50 lb N/a fish fertilizer (split 7x from mid-Apr. through June
about every 2 weeks. In 2010-12, 90 lb N/a was applied with half of the total N from Leafy Green (a
pelletized plant based fertilizer) applied in early March and half from fish fertilizer (split into 7
applications from mid-April through June). In 2013, the total targeted N rate was increased to 125 lb
N/acre with 60 lb N as Leafy Green and 65 lb N/acre as fish fertilizer (split as in prior years). Fish fertilizer
was applied as a liquid drench, by hand, around plants in 2007-2009. In 2010, fish was applied as a liquid
drench, by tractor, in a broadcast band over the row surface. In 2011-2013, fish was applied through the
drip irrigation system.
March 2014
Results
Yield and yield components: There has been no
effect of mulch treatment on percent fruit bud
set, flowers/cluster, percent fruit set, Brix, or
berry weight from 2009-13 (except for an effect
on berry weight in 2012), despite large
differences in plant growth due to soil pH and
nutrient differences. Mulch significantly affected
yield in 2009 and 2011 and cumulative yield from
2008-13 and berry firmness in 2009 and 2012. In
contrast, cultivar affected all variables except for
percent fruit set which was not affected by any
treatment from years 2 through 7.
Yield. Plants grown on sawdust+weed mat had a greater yield than those grown with compost+sawdust
in 2009 and in some cultivars in 2011. Cumulative yield (total yield from year 2 through year 7) was
affected by mulch type, but the response varied by cultivar (Fig. 1). There was little effect of pre-plant
incorporation/mulch type in Bluegold and Draper but large positive effects in many other cultivars.
Figure1.
Cumulative yield
(from 2008
through 2013) of
10 blueberry
cultivars grown
with compost &
sawdust
incorporated preplant and
compost +
sawdust mulch
(“Sawdust”) or no
pre-plant
incorporation and
sawdust mulch
covered with
weed mat
(“weedmat”).
Yield progression over the 6 fruiting seasons as plants matured varied by cultivar with some increasing
rapidly (e.g. Legacy, Ozarkblue), some increasing at a steady pace (e.g. Bluecrop, Reka, Aurora) and
others at a slow rate (e.g. Duke, Draper). Some cultivars had little change in yield from years 5-7 (e.g.
Duke, Bluejay), whereas some had a large increase in year 7 relative to prior years (e.g. Liberty, Aurora).
For most cultivars, yield was relatively high in 2013. These yields would be considered typical
“commercial” yields for some cultivars and lower or higher than typical for others. For example, in 2013
yield ranged from 4 to 6 tons/acre in Duke (the lowest yielding cultivar), Draper, Bluegold, and Bluejay, 9
to 11 tons/acre in Liberty, Bluecrop, Aurora, and Reka, and 16 to 17 tons/acre in Legacy and Ozarkblue.
Percentage of fruit buds set was higher for most cultivars in 2013 compared to past years, ranging from
37 to 52%, contributing to the higher yield. Some cultivars have had variable fruit bud set over the last
five years (e.g. Liberty has ranged from 38 to 54%; Legacy from 33 to 45%; Aurora from 34 to 51%;
March 2014
Bluecrop from 22 to 45%), whereas others have been relatively consistent (e.g. Duke 40 to 48%, Draper
40 to 51%); fruit bud set of Bluecrop has been relatively low the last couple of years (22 to 24%).
Flower number per cluster (or per bud) has been quite
consistent through the study, indicating a strong genetic
control for this factor. Cultivars with the fewest number of
flowers per bud (~6-8) included Duke, Draper, Bluegold,
and Legacy, whereas the highest flowers/bud (8-11) were
found in Reka, Bluecrop, Aurora, Liberty, and Ozarkblue.
Flowers/bud may have declined in 2013, because so many
more fruit buds set per lateral.
Percent fruit set ranged from 90 to 100% in 2009, 83 to
95% in 2010, 81 to 99% in 2011, 86 to 96% in 2012 and 86
to 96% in 2013 and was not affected by cultivar or mulch
type. It is clear that most flowers become berries in this crop in our region even though fruit set can be
reduced with poor weather during bloom, particularly in some cultivars.
Berry weight has varied from year to year for many of the cultivars.
Berry weight was greatest for all cultivars in the first year of harvest
(year 2, 2008) as is typical for young plants. Within cultivar, berry
weight appeared correlated with yield – in years with high yield (a
result of high fruit bud set, high flowers/bud or lighter pruning),
berry weight declined. However, berry weight was within
acceptable commercial standards for all cultivars in all years. In
2012 only, berry weight was greater on weed mat than on the
organic mulch treatments.
Percent soluble solids. There was a cultivar effect on percent soluble
solids (Brix) in 2009-2011, but not in 2012-13. In 2013, Brix averaged
13.7% (no cultivar or mulch effect).
Firmness. Cultivars differed in fruit firmness in all study years with
the firmness of Draper standing out among the rest of the cultivars. In 2009 and 2012, fruit were
significantly firmer on plants grown with the organic mulches than with sawdust topped with weed mat.
Yield Progression: Cultivars range from early (Duke and Reka) to late (Aurora) ripening. The percentage
of yield harvested on each pick date is shown in Figure 2.
Figure 2. Yield
progression of
cultivars in
2013 (year 7)
at the NWREC.
March 2014
Over this six year study, we have confirmed considerable overlap among cultivars in the bloom period.
However, early ripening cultivars have a shorter GDD requirement from full bloom to first harvest
compared to late ripening cultivars.
Acknowledgements: We thank the following individuals for their significant contributions to this
project: Gil Buller (Senior Research Assistant, NWREC) and Emily Vollmer (former Research Assistant,
dept. Horticulture, OSU).
We greatly appreciate the financial, research grant support and in-kind contributions from: Oregon
Blueberry Commission; Eric Pond (AgriCare Inc.), Fall Creek Farm & Nursery, Wilbur Ellis, Marrone
BioInnovations (GreenMatch), Cutting Edge Formulations (AvengerAg) and Oregon Tilth.