March 2014
Weed and fertility management of a certified organic blueberry field
Author: Amanda Vance, Research Assistant, OSU NWREC
Project Leader: Bernadine C. Strik, Professor of Horticulture, OSU NWREC
Project Collaborator: David Bryla, Research Horticulturist USDA-ARS, HCRU
Objectives:
The long-term goal of this project is to develop organic production systems for highbush blueberry that
maximize plant growth, yield, and fruit quality; facilitate weed, water and nutrient management, and
provide economic benefit to growers. Specific objectives are to:
1) determine the effect of raised beds on soil and plant water status, growth, and weed management
2) study organic weed management systems for effectiveness and economic feasibility
3) ascertain the effectiveness of organic fertilizer treatments for yield, plant nutrient status, and growth
4) determine whether an early and late-fruiting cultivar differ in ease of organic management
5) develop economic analysis and comparisons among treatments at end of study
Treatments:
A) Planting method: Raised bed or flat ground;
B) Cultivar: ‘Duke’ and 'Liberty';
C) Weed management:
1) sawdust mulch (3-4”) + hand weed management;
2) compost (yard debris, 1-2” deep) + 2” sawdust mulch + organically-approved herbicides (e.g
vinegar or GreenMatch/AvengerAg) and hand weeding, as needed; (replenished in Jan.
2011 and 2013, as needed).
3) landscape fabric (weed mat) with sawdust mulch (2” deep) in the 8" diameter plant hole;
Weed mat was replaced Dec. 2010 with “zippered” system
D) Organic fertilization:
Source:
1) feather meal: Split 2x [March and May] applied to surface of mulch around plant when young
and as broadcast band when canopy was full (2010-present)
2 fish emulsion: Liquid drench to mulch surface around plants (under weed mat; 2007-2010) or
via drip under mulches (2011-present); split 7x [mid- Apr. to early July; every 2 weeks].
Rate:
1) Low rate: 25 lb N/a (2007-09); 50 lb N/a (2010-12); 65 lb N/a (2013-present)
2) High rate: 50 lb N/a (2007-09); 100 lb N/a (2010-12); 125 lb N/a (2013-present)
March 2014
Progress to date (emphasis on 2013 results):
Yield was affected by cultivar in 2013, as has been the case in past years (Figure 1). We had difficulty
controlling birds on our early ripening ‘Duke’ in 2013 and we feel the loss in ‘Duke’ yield this past season
was almost exclusively due to bird depredation.
Figure 1. Effect of cultivar on average yield in tons/acre (averaged over fertilizer source and rate, mulch and raised/flat)
from 2008 – 2013 (year 2 through 7). Cumulative yield on right.
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Yield was 13% greater on raised beds than on flat
ground, on average. However, the effect differed by
cultivar, as ‘Duke’ had a similar yield whether grown
on flat or raised beds, whereas ‘Liberty’ had a
greater yield on raised than on flat ground.
Cumulative yield (2008-13) has averaged 22%
greater on raised beds.
The response of plants to mulch type in 2013 was
affected by the type of fertilizer used. With weed
mat mulch, yield was greater when feather meal
was used (low or high rate) than when the high rate
of fish was applied. In contrast, fertilizer type or rate
had no effect when compost+sawdust or sawdust
mulch was used.
Cultivars have responded differently to fertilizer source/rate, and 2013 was no exception. In
‘Liberty’, there was no effect of fertilizer source or rate on yield whereas in ‘Duke’, fertilization with
feather meal produced the highest yield. In ‘Duke’, fertilization with the low rate of fish emulsion led
to greater cumulative yield than with the high rate of fish.
Quality—2013
Berry weight. Plants grown on raised beds
produced significantly larger berries (2.3 grams)
than those grown on flat ground (2.2 g) and plants
fertilized with fish emulsion produced larger fruit
(2.3 g) than those fertilized with feather meal (2.2
g).
Brix (percent soluble solids) was not affected by
raised beds vs. flat, mulch type, or fertilizer source.
March 2014
‘Liberty’ fruit had a higher Brix (15.6%) than ‘Duke’ fruit (13.0%).
Firmness. Plants fertilized with the low rate of feather meal produced less firm fruit than those fertilized
with the high rate of feather meal or fish emulsion. There was no effect of raised vs. flat or mulch type
on firmness. ‘Duke’ produced firmer fruit (176 g) than ‘Liberty’ (158 g).
Plant nutrients (all nutrients were
analyzed, only nitrogen, potassium and
calcium presented here):
Nitrogen: Treatment effects on leaf %N
were complicated in 2013 with
interactions between planting method
and mulch type, fertilizer and mulch, and
cultivar differences. Leaf tissue %N has
been below recommended standards for
many or all treatments (depending on year). Leaf %N has not been correlated with yield, despite most
treatments having “commercial” yields. Plants fertilized with the high rate of fish emulsion (lowest
yielding ‘Duke’ fertilizer treatment) have had the highest %N. Tissue %N was higher for ‘Duke’ than for
‘Liberty’ in 2013, with the opposite found in 2012.
Potassium: Plants grown on raised beds had a greater leaf %K (0.51%) than those grown on flat ground
(0.48%) in 2013. Plants fertilized with fish emulsion had higher leaf %K, especially when grown with
compost+sawdust or weed mat mulch. Fish emulsion is high in K relative to feather meal. ‘Duke’ has had
a lower leaf %K than ‘Liberty’ in all years, including 2013.
Calcium: Leaf %Ca was higher when plants were fertilized with feather meal (0.57%) than with fish
emulsion (0.51%). Feather meal contains more Ca than fish emulsion.
Soil Nutrients: Soil nutrient levels were affected by mulch type. Soil pH declined over time in most
treatments and was lowest in the sawdust mulched plots and highest in the weed mat. Mulching with
compost+sawdust increased soil organic matter relative to all other treatments. Organic matter declined
over time under the weed mat. Soil K increased with use of compost+sawdust mulch and the effect of
mulch on soil K levels patterned what was seen in leaf %K. Soil nitrate levels, measured under the mulch
in October 2013, were higher under weed mat and compost+sawdust than under sawdust alone.
Summary: This planting will be considered “mature” in 2014. To date, growth and yield for many
treatments have been similar to what is commonly observed in conventional systems. In general, the
best treatments so far have been growing plants on raised beds with a low rate of fish emulsion or a
high rate of feather meal on either weed mat or compost+sawdust mulch. The high weed management
costs of using compost as a mulch (likely because
weed seeds germinate readily in the nutrient rich
compost) need to be carefully considered for
organic management. Also, the long-term impact
of higher soil K (and any adverse effects on plant
uptake of other cations, e.g. Ca and Mg) with use
of compost needs further study. Conversely, the
negative impacts of weed mat use on soil organic
matter also requires further investigation.
March 2014
Acknowledgments:
Thank you to everyone who has assisted in the development and management of this project, including
Gil Buller (Senior Research Assistant, NWREC/OSU), Dan Sullivan (Assoc. Professor, Crop and Soil
Science, OSU), Dave Bryla (USDA-ARS, HCRU Corvallis) and the members of our advisory committee: Nick
Andrews (OSU), Charlie Prade (organic grower, OR), Eric Pond (organic grower, OR), Adam Wagner
(Organically Grown Company, OR), Steve Erickson (Pan American Berry Growers, OR), Chrislyn Particka
(formerly, Sakuma Bros. research, WA), Joe Bennett (Pacifica Organic Advisors, WA)
We appreciate funding from the Northwest Center for Small Fruits Research; Oregon Blueberry
Commission; NIFA-OREI (Formula Grant no. OREI 2008-513000-04443); Washington Blueberry
Commission as well as in-kind contributions and support from AgriCare Inc., Oregon Tilth, Oregon Dept.
Ag-GAP Certifier, Wilbur-Ellis, Marrone Bio Innovations Inc. & Cutting Edge Formulations Inc., AgroThrive
Inc., Bird Guard LLC.