Download Nutrient management

OSU BLUEBERRY SCHOOL
March 16-17, 2015
held at
Oregon State University, Corvallis, Oregon
This two-day blueberry “school” was organized for new and experienced blueberry growers,
farm managers, crew leaders, advisors, packers/shippers, and consultants. Experts from Oregon
State University, USDA Agricultural Research Service, Washington State University, and the
blueberry industry were asked to address key issues of where the blueberry market is going; how
you might be more successful in tight labor or volume markets; which cultivars are easiest to
grow and are in most demand; how to establish new acreage using cutting-edge methods;
projected costs and the resources available to growers for selecting new planting sites; how to
best manage existing acreage to maximize returns of high-quality fruit; provide basic information
on blueberry plant physiology to help growers minimize environmental stresses and improve
yield potential; nutrient management programs for optimal growth and quality; irrigation and
fertigation practices for higher quality and better efficiency; use of organic amendments and
mulches; planning for and improving machine harvest efficiency; pruning for hand or machine
harvest (where can you cut corners….or not), maximizing pollination for good fruit and seed set;
overviews of the most important blueberry viruses, diseases, insects, weeds, and vertebrate pests;
and tools for good pest management. Information throughout the program addresses the needs of
conventional, transitional, and organic growers. Simultaneous interpretation to Spanish has been
provided. This proceedings book contains information provided on these topics by each speaker
and co-authors. The thumb drive provided in the registration packet for each attendee includes a
copy of each presentation. Thank you for attending. It is our sincere wish that this will be a very
useful meeting and that you find the accompanying materials a valuable reference! –
Bernadine Strik, Professor and Extension Berry Crops Specialist, OSU and the members of the
organizing committee
Organizing Committee
Bernadine Strik, Chair, Oregon State University (OSU)
Wei Yang, OSU. Co-chair (sponsorship coordinator), OSU
Donna Williams, Rachel Williams & team at OSU Conference Services
Dave Bryla, USDA-ARS HCRU
Chad Finn, USDA-ARS HCRU
Vaughn Walton - OSU
Steve Castagnoli - OSU
Steve Renquist - OSU
Bryan Ostlund – Oregon Blueberry Commission
Eric Pond - industry
Jon Umble – industry
Derek Peacock - industry
Steve Erickson - industry
Nancy Jensen - industry
i
Table of Contents
OSU Blueberry School
Title
Authors
Characteristics of production regions in the Pacific
Northwest
Lisa DeVetter, Pat Jones, Bernadine
Strik, Kathie Dello
1
Markets - what's the future for fresh, processed, and
organic markets? Things you MUST think about before
starting or expanding production
Rod Cook, Derek Peacock, Jeff
Malensky, David Granatstein
9
Cultivar choices- Tried and true to brand new
Chad Finn and Bernadine Strik
15
Economics of production – resources
Bernadine Strik and David Granatstein
29
Resources available for selecting a good blueberry site
Wei Q. Yang
37
Site selection and establishment of a blueberry field
Wei Q. Yang and Bernadine Strik
41
Organic soil amendments and mulches for blueberry:
the good, the bad and the ugly
Dan Sullivan (OSU)
47
On-farm irrigation system design and operation
David Bryla
53
Blueberry plant physiology - why it's important to
understand the plant to manage it well
Bernadine Strik
57
Irrigation scheduling: when, where, and how much?
David Bryla
63
Pruning - impact of plant age, cultivar, and harvest
method
Bernadine Strik
69
Harvesting - hand vs. machine
Bernadine Strik (moderator); Paul
Norris (Norris Farms); Frank Brown
(Littau Harvesters (Inc.); Doug
Krahmer (Berries Northwest)
75
Nutrient management of blueberry -- assessing plant
nutrient needs and designing good fertilizer programs
Bernadine Strik and David Bryla
79
Maximizing pollination in blueberry
Ramesh Sagili, Carolyn Breece, John
Borden
95
Blueberry viruses present in the Pacific Northwest and
suggestions for their management
Robert Martin
99
Blueberry bacterial and fungal diseases
Jay Pscheidt and Jerry Weiland
107
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Page
Title
Authors
Page
Weed management for blueberry fields in the Pacific
Northwest
Tim Miller
115
Getting hit high and low: Options for managing bird
and vole damage
Dana Sanchez (OSU
125
Management of arthropods, insect, and plant-parasitic
nematodes in blueberries
Vaughn Walton,Nik Wiman, Inga
Zasada, Joe DeFrancesco, Daniel
Dalton, Amy Dreves, Jana Lee, Lynell
Tanigoshi, Wei Yang
129
iii
Nutrient management of blueberry – Assessing plant nutrient needs and
designing good fertilizer programs
1
Bernadine Strik1 and David Bryla2
Department of Horticulture, Oregon State University
2
USDA-ARS Horticultural Crops Research Unit
This summary is a supplement to the nutrient management guide available online at Oregon State
University (https://catalog.extension.oregonstate.edu/): Nutrient Management for Blueberries in
Oregon, EM 8918. A revision of this guide is planned within the next year or so to incorporate
new information on organic fertilization, fertigation, and tissue testing. In addition, see other
resources in the “references” section.
In this article and presentation, we will address recommended soil nutrient levels for making preplanting decisions, starting rates of key nutrients to apply, how to assess plant nutrient status to
modify fertilizer programs, timing and source of fertilizer to apply, and fertigation.
Key questions that need to be answered with regard to any nutrient management program are:
How much nutrient should be applied? When is the best time to apply the nutrient? What is the
best source of the nutrient for the plant? And what is the best method to apply the nutrient?
Proper fertilization or excess fertilizer will not compensate for poor growth that is caused by
poor soil drainage, other management problems, or disease, weed, or insect problems.
Pre-plant soil testing and other considerations
Soil test. Soil testing is important to adjust soil nutrient status prior to planting. This not only gets
the plants off to a good start, but incorporation of nutrients that are immobile or do not move
readily into the rooting zone with a surface application is very effective (e.g. lime). See
“additional resources for more information”.
Prior to planting, base the rate of nutrients to be incorporated into the soil on recommended soil
nutrient sufficiency levels (Table 1). Testing soil to predict nitrogen (N) application rates is not
advised.
Soil pH. Blueberry plants are adapted to a low pH (4.5 to 5.5; Table 1). At this pH, nutrients are
more available to the plant. If soil pH is too high, which is not uncommon in the Willamette
Valley when other crops like grass seed or mint have been grown, then soil pH must be lowered
prior to planting using elemental sulfur (S). In blueberry, be conservative on addition of sulfur to
acidify the soil, because if the soil pH drops too low, raising the pH to the target range after
planting (using lime) is difficult. The recommended rate of elemental S to apply is based on the
starting soil pH, the soil type, and the desired pH. We suggest targeting a starting soil pH of 5.5
or 5.6 as fertilization lowers soil pH over time (see below). Incorporate the recommended rate of
elemental S into the top 6 inches of soil at least 6 months (preferably a year) prior to planting – it
takes time for the S to react with water to lower soil pH. Test the soil again several months prior
to planting and modify again, if needed, based on the new soil test results. If the soil pH does not
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require much modification (less than 0.3 pH units), then you can incorporate the S and plant the
field using container-grown stock within a couple of months of each other.
If the soil pH is too low (not uncommon in western Oregon when converting long-term
perennial, fertilized crops to a new blueberry field), then the appropriate amount of lime should
be applied. It is best to do this at least 6 months prior to planting.
If calcium is needed, but the soil pH is in the desired range, then apply gypsum.
It is best to carefully review the publications available on soil pH modification to ensure that the
correct amount of S or lime is applied for the desired result (see “Resources”) and to consult with
Extension faculty and crop advisors in advance.
Table 1. Suggested critical sufficiency levels for nutrients in soil for blueberry production
Nutrient
pH (in water)
Unit
target:
4.5 to 5.5
Deficient at less than:
Phosphorus (P; Bray)
Phosphorus (Olsen)
Potassium (K)
Calcium (Ca)
Magnesium (Mg)
Manganese (Mn)
Boron (B)
ppm
ppm
ppm
ppm
ppm
ppm
ppm
25 to 50
10
100 to 150
1000
60
20
0.5
EC
dS/m
<2
Amendments. Use caution when incorporating organic materials into the soil prior to planting.
While some materials that are commonly used in blueberry (e.g., sawdust) have little effect on
soil pH, many materials may increase soil pH. For example, horse straw/bedding, animal
manures, and various composted materials (including yard debris compost) have a pH ranging
from 7 to 8. Some also have a high salt content (i.e., high electrical conductivity or EC). For this
reason, incorporation of these materials, “as is”, is not recommended prior to planting blueberry.
When planning to use a new, unknown product in blueberry production, we encourage growers
to test the product for pH, EC, the carbon to nitrogen ratio (C:N), and nutrients, in order to
decide whether or not the material is suitable for blueberry, and to help manage the nutrient
program.
Nutrient assessment after planting
Soil test. After planting, annual soil sampling is not needed unless you are correcting a problem.
We recommend soil samples be collected every two to three years to monitor changes in soil
nutrient status. Use the sufficiency levels in Table 1 as a guide. Testing soil to predict nitrogen
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(N) application rates is not advised. However, testing the soil for high N concentration in late
summer/fall can be used an indicator of excessive N fertilization.
Standard fertilization programs lead to acidification of the soil in the row – the pH will thus
decrease over time in all blueberry production systems, including organic. Generally, for every
100 lb of N applied per acre in a typical Willamette Valley blueberry field, soil pH will
decrease about 0.1 unit per year with urea and 0.2 units per year with ammonium sulfate.
It is thus best to monitor soil pH every few years. In most production systems, we recommend an
annual application of 500 lb lime/acre to help reduce the downward drift of soil pH. This may
not be needed when a high-pH mulch is included in the management program (e.g., the use of a
high pH compost as part of a fertility or mulch program, as is common in some organic
production systems).
In established fields, sample soil at the same time of year, so that years can be more easily
compared. Soil pH fluctuates over the season and, in western Oregon, is generally lowest in
autumn and highest in late winter. Do not collect soil samples in spring, right after fertilization
has occurred.
Collect soil samples in the plant row (where the fertilizer is applied) and, in drip irrigated fields,
sample within a few inches of a drip emitter in all sub-sample locations. If mulch is present,
remove the mulch layer before taking the soil sample. Sample from the soil surface to about 1 ft
deep.
Tissue testing. Leaf tissue analysis provides information on the nutrient content of the plant.
Sometimes, even when the soil nutrient content is adequate, the plant is not able to take up the
nutrients required (e.g., when soil pH is incorrect; in dry or waterlogged soils; during cool
weather; and when cultural issues such as with too much or insufficient irrigation). Tissue
standards have been developed using results from research experiments and estimated from large
databases that relate tissue nutrient levels to good yielding fields for each crop (OSU). We
conducted a study evaluating leaf tissue nutrients in six cultivars (Duke, Bluecrop, Draper,
Liberty, Legacy, Aurora) in conventional and certified organic, mature fields in 2013-14 (Strik
and Vance, 2015). Our results have helped us better inform growers of correct sampling times
and tissue standards.
In all berry crops, leaf tissue nutrient concentration changes throughout the season. The
recommended time of sampling leaves for tissue analysis is related to a period of time when the
leaf nutrient concentration is most stable in late July-early August in Oregon. This sampling time
has been used successfully in other production regions in the PNW. However, we do suggest
looking at leaf samples from your particular region to assess whether slight modifications to this
sampling time are needed (see below).
Tissue nutrient levels will also change with location or age of the leaf and what type of leaf it is.
In blueberries, the best leaves to sample are from shoots that are growing below the fruiting zone
– not from whips.
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When collecting leaf tissue samples:
 Sample at the correct time (late July to early Aug.); published tissue standards are NOT
correct if sampled at any other time of the season. Do NOT adjust sampling period
based on fruiting season of the cultivar – this is not necessary and will lead to poor
results.
 Sample cultivars separately. Cultivars differ in leaf nutrient status – again monitor over
the years and look for changes over time.
 If you are seeing problem plants at any time of the year, collect leaves from affected and
“normal” looking plants and compare tissue analysis results for clues as to the cause.
 Collect the right tissue – most recent, fully expanded leaves on shoots below the fruiting
zone in blueberry
 Do not wash leaves as soaking leaves may reduce tissue K. Note that any micronutrients
in fungicide applications, foliar nutrient applications, and dust on leaves can lead to
“higher” than typical nutrient results (keep records).
 Keep excellent records on cultivars and blocks sampled, time of year sampled, and any
associated yield or fruiting season information. It will be important to look for trends
over time.
 Tissue analysis and observations of plant growth are best used to plan for and adjust
nutrient management programs for the following year.
 Do not use just the tissue N concentration to adjust N fertilizer programs. Use
recommended fertilizer application rates as a starting point and, then, adjust programs
based on observations of tissue N AND plant growth.
 Be aware that tissue nutrient concentrations that are below or above the recommended
levels (Table 2) may indicate a soil problem (e.g., high tissue Mn may mean soil pH is
too low).
Symptoms of nutrient deficiency are sometimes apparent and will vary with the type of nutrient
and its mobility within the plant. Nutrients in the plant move in either the xylem (with water –
this tissue is dead) or the phloem (with “food” – this tissue is alive). Nutrients that move in the
xylem are not mobile within the plant, as they simply move with water to the leaves (not from
leaves to the fruit or from old leaves to new leaves, for example). Nutrient deficiencies of
immobile nutrients (S, Fe, Mn, Cu, Zn, Ca, and B) are in the new leaves. Nutrients that move in
the phloem are mobile within the plant. The nutrients that are mobile in the plant are: N, P, K,
Mg, and Cl; symptoms of deficiency of these nutrients are on the older leaves.
If tissue testing indicates a nutrient is deficient, fertilization with this nutrient may be required.
Be cautious when applying boron, especially as a granular product – over-application of boron
can lead to boron toxicity.
Fertilization – rate and source
Blueberry evolved in soils with low nutrient content and therefore can survive with often
surprisingly low levels of fertilization. However, a good fertilization program is necessary for
rapid plant growth during establishment of the planting and to produce high yields in mature
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fields. Recommended rates of fertilizer to apply vary with planting age, soil nutrient status, and
growth, vigor or planting productivity.
Table 2. Recommended leaf tissue sufficiency levels for blueberry when sampled in late-July to
early August)
Nutrient
Nitrogen (%N)
Phosphorus (%P)
Potassium (%K)
Calcium (%Ca)
Magnesium (%Mg)
Sulfur (%S)
Manganese (ppm Mn)
Boron (ppm B)
Iron (ppm Fe)
Zinc (ppm Zn)
Copper (ppm Cu)
Aluminum (Al)
Northern Highbush
Current standards
1.76 to 2
0.11 to 0.4
0.41 to 0.7
0.41 to 0.8
0.13 to 0.25
0.11 to 0.16
31 to 350
30 to 80
60 to 200
8 to 30
5 to 15
na
Northern Highbush
Revised standards
1.76 to 2.0
0.10 to 0.20
0.40 to 0.65
0.45 to 0.85
0.13 to 0.25
0.11 to 0.16
31 to 350
30 to 80
60 to 200
8 to 30
3 to 10
40 to 160
Southern Highbush
Current standards
1.8 to 2.1
0.12 to 0.40
0.35 to 0.65
0.4 to 0.8
0.12 to 0.25
0.12 to 0.25
50 to 350
30 to 70
60 to 200
8 to 30
5 to 20
na
Rabbiteye
Current standards
1.2 to 1.7
0.08 to 0.17
0.28 to 0.60
0.24 to 0.7
0.14 to 0.2
na
25 to 100
12 to 35
25 to 70
10 to 25
2 to 10
na
Rabbiteye leaf standards from Krewer and NeSmith, Blueberry Fertilization in Soil, Fruit Pub.
01-1, Univ. Georgia (date unknown).
http://www.smallfruits.org/Blueberries/production/blueberryfert.pdf
Note the proposed revised tissue standards in the second column based on recent research (Strik
and Vance, 2015)
Efficiency of plant uptake of a fertilizer is affected by plant age (depth and width of root zone),
presence of a surface mulch, amount of coverage of the in-row area (plants that fill the row space
have a greater efficiency of uptake than those that do not), method of application (efficiency
varies with granular, liquid, or foliar applications), and the amount and timing of fertilizer
applied. Recommended rates thus may vary among application methods and plant age. Applying
higher than recommended rates of fertilizer can have adverse effects on plant productivity, fruit
quality and the environment.
Nutrient “removal”
Nutrients that are removed in harvested fruit and wood when pruning, in addition to the nutrients
needed for plant growth must be considered when planning nutrient management programs. Our
research has shown that nutrient removal in harvested fruit varies slightly by cultivar, but is very
dependent on yield. The amount of nutrient per ton of fresh fruit harvested is shown in Table 4.
For example, an estimated 13 to 27 lb N/acre is removed in a 10 ton/acre blueberry crop. In
blueberry, the wood removed when pruning is often flailed (chopped) between the rows.
However, unlike raspberry and blackberry, for example, there are no blueberry roots between the
row middles. Any nutrients that recycle into the soil are thus not available to the blueberry plant
and are considered “removed”. Based on our research approximately 14 lb N/acre is removed
when pruning a mature planting (Table 3).
It is clear from these data that blueberry plants do not have a high nutrient demand compared to
many crops. For a mature field that has a yield of 10 ton/acre, for example, the amount of
nutrient removed, including pruning, is 26 to 37 lb N/acre, 2.5 to 4.5 lb P/acre, 14.5 to 23.5 lb
K/acre, 4 to 5 lb Ca/acre, 1.3 to 1.9 lb Mg/acre, 0.4 to 0.5 oz B/acre, 0.6 to 0.7 oz Cu/acre, 12.5
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to 13.1 oz Mn/acre, 0.6 to 0.9 oz Zn/acre, and 1.6 to 2.1 oz Fe/acre (Table 3). Some additional
nutrients would be required for growth.
Table 3. Nutrient removal in blueberry per ton of fruit harvested (fresh weight) and per acre of
wood removed when pruning.
Part removed
Fruit (per ton harvested)
Prunings (per acre)
N
P
1.3 - 2.3
0.1 - 0.3
14.0
1.5
B
Fruit (per ton harvested)
Prunings (per acre)
Macronutrients (lb)
K
Ca
0.8 - 1.7
0.1 - 0.2
6.5
3.0
Micronutrients (oz/ton)
Cu
Mn
Zn
Mg
S
0.05 - 0.1
0.06 - 0.2
0.9
1.1
Fe
0.02 - 0.03
0.01 - 0.02
0.04 - 0.1
0.01 - 0.04
0.05 - 0.1
0.2
0.5
12.1
0.5
1.1
Range in fruit nutrients provided for cultivars studied: Duke, Bluecrop, Draper, Liberty, Aurora,
Legacy, Elliott (Strik, in progress)
Nutrients in pruning wood from research done in mature 'Elliott' (Strik, in progress)
Nitrogen
Nitrogen (N) is the primary nutrient applied to blueberry and is usually needed each year. Use
recommended N application rates in Table 4 as a starting point. Additional N may be needed
when fresh mulches with a high carbon to N ratio (e.g. sawdust) are applied. Split applications or
fertigate at the correct timing to increase plant uptake and meet plant demand (see below). While
tissue N levels (Table 2) can be useful to assess plant N status, leaf N levels may also be
misleading. For example, a low leaf N may be caused by dilution of N in the leaf due to rapid
growth (can be an issue on young, low yielding plants or when whips are sampled instead of
laterals); above normal N in a leaf test may be related to weak or stunted growth, and not due
necessarily to excessive fertilization. Observations of plant growth must be coupled with tissue N
results to interpret N fertilization programs. If leaf N is within the sufficiency range (Table 2)
and growth is good, no adjustment of fertilizer is needed. If tissue N and growth are above
normal, then reduce application of N. If leaf N and growth are poor and other management issues
seem appropriate, then increase rate of N, but evaluate why your farm may need more N than
recommended (Table 4); for example, you may have applied fresh mulch recently, which is
immobilizing some of the fertilizer N applied.
When plants are low in N, shoot growth is poor, and due to insufficient chlorophyll, the leaves
turn pale green or yellow (chlorosis) and often develop a reddish tinge. The yellowing occurs in
older leaves first and is uniform across the entire leaf surface (i.e., no particular color pattern or
mottling).
Recommended N rates vary with planting age (Table 4). When plants are young and the canopy
does not fill the row, we recommend applying fertilizer by hand to reduce fertilizer use and
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improve efficiency of uptake, as fertilizer is only placed above the root area. Spread the
recommended rate in an area under the drip line of the bush where the roots are. Apply fertilizer
evenly. Do not leave “clumps” of fertilizer touching the plant base or crown as this can burn
plant tissues. Recommended rates in Table 4 for granular fertilizers are based on a per plant
application in the first and second growing seasons assuming canopies of adjacent plants are not
yet touching. If you are going to use a fertilizer spreader then calculate how much of the
broadcast band applied will not be above the roots (under the drip line of the bush) and increase
the rate accordingly. For example, if only 60% of the granular fertilizer is applied under the bush
then divide the recommended rate by 0.60 to calculate the total amount of N to apply. Remember
to convert the N rate to the amount of product to apply (e.g., 100 lb N/acre of ammonium sulfate
[21-0-0] would be 100 ÷ 0.21 = 475 lb product/acre). See sources of nutrients for more
information.
Table 4. Recommended rates of nitrogen (N) to apply based on planting age and application
method (granular or fertigation).
Recommended N rate (lb/a)
Granular fertilizer
Year
Fertigation
Oregon*
British Columbia†
**
1
90
25-40
19
**
2
90
40-50
27
3
60
50-60
45
4
70
55-65
50
5
75
65-75
65
6
85
80-100
70
7
95
90-120
90
8+
100-150
100-140
100
*
Based on an in-row plant spacing of 2.5-3.0 feet; Nutrient Management for Blueberries in
Oregon (Hart et al., 2006). These rates have been modified from Hart et al. (2006) for a field
without surface mulch. If a sawdust mulch is used and replenished every 3 years add 25 lb N/a
to the recommended granular rate.
**
The rates for year 1 and 2, Oregon assume application to the root zone area by hand. If a
granular spreader is used then increase rate to account for inefficiency of application method. We
assume that the plant canopies will be touching at the 2.5 to 3 ft spacing in year 3.
†2014 Berry Production Guide - Beneficial Management Practices for Berry Growers in
British Columbia.
1 lb/acre = 1.12 kg/ha.
The rates in Table 4 for granular applications in Oregon assume no surface sawdust mulch is
present (e.g., bare soil or when granular N is applied under weed mat such as when using feather
meal or soybean meal in organic systems). Douglas-fir sawdust mulch generally has a carbon-tonitrogen ratio of 800:1. Research has shown that more fertilizer N is needed when granular
products are applied to the top of a sawdust mulch. For example, if you apply an additional 11
units of sawdust (2 inches deep in 3-foot-wide bands on 10-foot centers), you will need to add 25
lb N/acre to compensate for N immobilized by the fresh sawdust. However, adjust N rates, if
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necessary, in all plantings based on observations of growth, tissue analysis, and the amount and
type of mulching.
Blueberry plants require very little N fertilizer, especially in the fertile soils found in many
regions of the PNW. For example, our research has shown that there is no added yield response
from N fertilization rates greater than 50 lb N/acre in a 9-year-study in Elliott (Strik in progress).
For this reason, the recommended rates of N in Table 4 should only be used as a guide. Plants
may grow very well at lower rates of N. In an 8-year study in certified organic blueberry,
‘Liberty’ plants did equally well when fertilized at low (25 to 65 lb N/acre from year 2 through
8) or high (50 to 125 lb N/acre) rates of feather meal or fish emulsion, when the plants were
grown with either a sawdust and compost mulch or weed mat; however, ‘Duke’ plants had the
lowest yield when fertilized with the high rate of fish (Strik et al., in progress). Try the lowest
recommended rate of N for ‘Legacy’, as this cultivar can easily become “vegetative”, setting
fewer fruit buds, if fertilized with higher rates of N.
Fertilizing with rates of N that are in excess of plant needs have been observed to lead to late
shoot growth and reduced fruit bud set (thus reducing yield the following season). Late shoot
growth also delays dormancy and increases the plant’s susceptibility to damage from early cold
spells. Even though fertilizers with ammonium-N are applied to blueberry fields, nitrification
(changing ammonium to nitrate-N) occurs, albeit slowly at the low soil pH found in blueberry
fields. Fertilization with excess ammonium fertilizers can thus lead to excess soil nitrate in the
fall.
Rabbiteye blueberries need much less N than do highbush blueberries and will have poor growth
and yield with over-fertilization. Grower experience has indicated that N rates can be reduced by
up to half for rabbiteye blueberries with good results.
Potassium
The nutrients required most by blueberry are N and potassium (K). Soil K and leaf K should be
monitored as described above. Annual applications of K (as K2O) at a rate of 50 lb/acre are
commonly done (41.5 lb/acre of elemental K). However, K fertilization is not needed if soil K
levels and tissue levels are sufficient. Note that tissue K may fluctuate from year to year due to
differences in yield (lower leaf K in a high yield year). Our research has shown that while the
best time to sample for leaf nutrient status is late-July to early-August for all cultivars, there can
be significant differences among cultivars in leaf K, likely based on fruiting season; for example,
‘Aurora’ and ‘Duke’ have a higher leaf K than ‘Legacy’ and ‘Liberty’, and ‘Draper’ also tends to
have a lower leaf K than ‘Bluecrop’, ‘Duke’ and ‘Aurora’ (Strik and Vance, in progress).
Application of other fertilizer nutrients should be based on soil and tissue analysis. As mentioned
previously, be cautious when applying boron fertilizers as there’s a fine line between sufficiency
and toxicity.
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Source of fertilizer
There are two forms of N that can be found in inorganic fertilizers – ammonium (NH4) or nitrate
(NO3). Blueberry plants only take up the ammonium form of N (found in urea and ammonium
sulfate). Organic sources of fertilizer contain ammonium N.
Soil pH affects nitrification – or the rate an ammonium-N fertilizer is nitrified to nitrate-N. At a
soil pH of 6.0, fertilizers containing ammonium-N (e.g., urea, ammonium sulfate) are rapidly
nitrified to nitrate-N (80% converted in 6 weeks). In contrast, at a pH of 5.5, nitrification is much
slower (30 to 40% in 6 weeks). Blueberry plants take up ammonium-N; keeping soil pH at 4.5
to 5.5 delays nitrification, keeping the ammonium fertilizer in a form that can be taken up by the
plants.
Use of fresh manures is not recommended as a fertilizer source in berry crops. Organic growers
may use compost (yard debris or chicken) as a surface applied mulch/fertilizer product. We
recommend testing any composted materials to ensure you know the pH and what nutrients are
being applied to the field.
Fish emulsion (applied as tank spray or through the drip system) or feather meal (granular) are
good sources of N (also contain other nutrients; Table 5). If you are using fish fertilizer, dilute
the product 1:10 (v/v fish:water) before applying to avoid burning the plants (straight fish has an
EC of ~ 20 dS/m). We have found the N in these products to be available quickly. Apply fish at
the same rate (of N) and timing as for the inorganic products. Apply feather meal (at same total
rate of N) in a split application where half is applied in early March and the other half in midApril – applying this product too late reduces N availability to the plants. Other organicallyapproved products may be available. Products also differ in the proportion of N available during
the season (Table 5). Organic sources of fertilizer can vary tremendously in the cost per pound of
actual N applied.
Table 5. Typical nutrient content of common organic fertilizers. Note nutrient content may vary
significantly among products and even among batches/years. From PNW 646 (see “Resources”)
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When to apply fertilizer nutrients
In blueberries, apply fertilizer N from early bloom through mid-June to mid-July, depending on
soil fertility, growing region, and method of application and rate of N being applied. Blueberry
plants will NOT take up N fertilizer that is applied in late winter – N fertilizer uptake starts at
bloom. In fields that are irrigated with sprinklers, split the recommended rate of granular N
fertilizer (Table 4) into thirds, with the first application in late April, the second in mid May, and
the third in mid June. In drip irrigated fields, the first application of N, applied when irrigation is
not yet required, can be done using a granular product. However, some growers, especially those
with weed mat mulch, still use fertigation for the entire N application period (see below).
Base fertilization with phosphorus (P), K, magnesium (Mg), and calcium (Ca) on soil and tissue
test results. If needed, apply these nutrients as granular fertilizers in fall or late winter to promote
their availability (rainfall). If tissue testing indicates plants have a micronutrient deficiency (most
commonly boron, B, in the PNW), then fertilize with a granular product (Borax) in the fall or
with foliar products (e.g. Solubor) just prior to leaf fall in autumn or just prior to bloom in the
spring. Be cautious with granular applications of micronutrients such as boron, as there is a fine
line between sufficiency and toxicity. See “resources” for more information.
Application of micronutrients to leaves during the season (foliar applications) is an efficient way
to get these nutrients to the targeted tissues. However, foliar applications are not very effective
for application of macro-nutrients (e.g. N, P, and K).
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Fertigation
Many blueberry fields are irrigated by drip. A major advantage of drip is the ability to fertigate.
Fertigation is the practice of applying soluble fertilizers to the plants directly through the
irrigation water. It is often a very efficient way to apply fertilizers because most roots in drip
irrigated fields are located near the drip emitters. Some advantages of fertigation include reduced
delivery costs (no need for tractors or spreaders), greater control of where and when the
fertilizers are placed, the ability to target application of specific nutrients during particular stages
of crop development, and the potential to reduce fertilizer losses by supplying only small
amounts of fertilizer to the plants as needed. Disadvantages include costs associated with the
need for higher fertilizer quality (i.e., purity and solubility) and the capital costs of the equipment
required to inject the fertilizer through the irrigation system.
Drip line placement. While nitrate-N is very mobile and moves readily in moist soil to plant
roots, ammonium-N moves much more slowly. Therefore, N in ammonium fertilizers will only
be available to the plants when it is applied close to the roots. Any ammonium-N applied away
from the roots will likely be nitrified and converted to nitrate-N and eventually will be leached
from the field by rain or irrigation.
To fertigate, drip lines and emitters should be located near the base of the plants during the first
year or two after planting and later repositioned 6-12 inches on each side of the plants, using two
lines per row, as the root system develops. Only one drip line per row is needed for adequate
irrigation of blueberry on most soil types, but two lines per row are suggested in order to
encourage a larger root system and thereby increase plant access to soil nutrients. The drip lines
should be installed under weed mat or buried under sawdust mulch to secure the lines and reduce
water runoff on raised beds.
Since only a fraction of the soil is wet by the drip emitters, most of the N applied to the plants
during fertigation is added directly to the roots. As a result, extra N is not required with
fertigation when sawdust or pine bark is incorporated into the soil prior to planting or used as
mulch (Table 4).
Timing and rate of N with fertigation. Liquid fertilizers should be injected in small and frequent
applications (e.g., once a week), starting at leaf emergence and finishing in late July or early
August. Fertigation is not recommended for the entire growing season (i.e., April–September)
because N applications in late summer reduce fruit bud set in blueberry and increase the potential
for freeze damage over the winter, particularly in colder regions such as eastern Oregon and
Washington.
Many growers using drip apply granular fertilizers in March or April and then switch to
fertigation in May, once irrigation is required on a regular basis. The use of granular fertilizer in
the spring is less expensive than fertigation and practical for mature plants. However, it may
cause fertilizer “burn” (salt damage to shoots and roots from the fertilizer) in new plantings and,
in severe cases, can kill young plants. Even small applications of ammonium sulfate applied at a
rate of 20 lbs/acre of N in the spring prior to fertigation reduced shoot growth and caused root
damage in young ‘Draper’ plants (Vargas and Bryla, 2015).
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The recommended N rates for fertigation are shown in Table 4. The rates are higher than those
recommended for granular fertilizers in Oregon and British Columbia during the first two years
after planting, but are similar to granular rates in the following years. Higher N rates are
recommended initially for fertigation due to low application efficiency in young plantings. Over
half of the emitters in drip tubing with standard 12 or 18 inch emitter spacings will end up
between the plants and outside of the root zone. Therefore, much of ammonium will be
unavailable to the plants. Granular fertilizer, on the other hand, is often applied by hand, directly
around the base of plants.
Fertilizer products available for fertigation. Unlike most crops, blueberry requires the
ammonium (NH4) form of N over the nitrate (NO3¬) form. Common inorganic sources of
ammonium or ammonium-forming fertilizers available for fertigation include:
 Ammonium nitrate solution or AN-20 (20-0-0) [NH4NO3•H2O] is ammonium nitrate
fertilizer dissolved in water. This product is commonly used for fertigation in fruit and
vegetable crops but is less suitable for blueberry due to the high concentration of nitrate
in the solution. Under no circumstances should concentrated AN-20 be mixed with
concentrated urea sulfuric acid, concentrated sulfuric acid, concentrated hydrochloric
acid, or concentrated phosphoric acid. NOT RECOMMENDED FOR BLUEBERRY.
 Ammonium polyphosphate (10-34-0 or 11-37-0) [(NH4PO3)n] contains 10-11%
ammonium-N but is used primarily as a source of phosphorus nutrition.
 Ammonium sulfate [(NH4)2SO4] is probably the most common source of N applied to
blueberry and is available in the liquid form (8-0-0-9S). Solutions can be made using dry,
granular ammonium sulfate (21-0-0-24S), which dissolves in water at a maximum
solubility of 6.3 lbs/gallon at 70 ºF.
 Ammonium thiosulfate (12-0-0-26S) [(NH4)2 S2O3] is typically used as an acidulating
agent but could also serve as potential N source for blueberry plants growing in high pH
soils. Research on this source of N for fertigation is planned for blueberry; in some crops
this fertilizer has caused some crop injury – caution is advised at this time.
 Calcium ammonium nitrate or CAN-17 (17-0-0-8.8Ca) [Ca(NO3)2•NH4NO3] is high in
nitrate-N, low in ammonium-N, and supplies calcium. Certain crops such as strawberry
and raspberry appear to produce higher quality fruit when fertilized with CAN-17, but
like ammonium nitrate solution, the fertilizer is too high in nitrate-N for blueberry. It
should not be combined with any products containing sulfates or thiosulfates. NOT
RECOMMENDED FOR BLUEBERRY.
 Urea solution (20-0-0 or 23-0-0) [(NH2)2CO] may be the most common liquid fertilizer
used for fertigation in blueberry. Urea rapidly converts to the ammonium form of N in the
soil but is less acidifying than ammonium fertilizers. It is also less costly per unit N and
can be made as a weaker dilution by mixing granular urea (46-0-0) in water at a
maximum solubility of 8.8 lbs/gallon at 70 ºF. Note that the solution will become
extremely cold as the fertilizer dissolves. Some growers are currently combining urea and
ammonium sulfate solutions to create a custom liquid fertilizer blend (20-0-0-5S) for
blueberry. Urea is the preferred fertilizer (over ammonium sulfate) in situations where
salt accumulation is of major concern.
 Urea-ammonium nitrate solution or UN-32 (UAN-32) (32-0-0) [(NH2)2CO•NH4NO3] is
manufactured by combining urea (46% N) and ammonium nitrate (35% N) on an equal N
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content basis. Of the available N sources, urea-ammonium nitrate has the highest N
concentration. It is marketed as a 32% N solution in warmer agricultural climates and as a
28% N solution in cooler agricultural areas. Urea-ammonium nitrate solutions should not
be combined with CAN-17 or solutions prepared from calcium nitrate. Thick, milkywhite insoluble precipitate forms, which could cause serious plugging problem.
 Urea sulfuric acid (various) [CO(NH2)2•H2SO4] is an acidic fertilizer that combines urea
and sulfuric acid. Combining the two materials eliminates many of the disadvantages of
using them individually. The sulfuric acid decreases the potential for volatilization losses
from the soil surface and ammonia damage in the root zone, while urea in the sulfuric
acid is much safer than sulfuric acid alone. This product is commonly sold under various
names such as N-pHURIC®. DO NOT MIX UREA WITH SULFURIC ACID ON
YOUR OWN (EXPLOSIVE).
Recently, fertigation and granular fertilization using different sources of N fertilizer during the
first five years of fruit production were compared in ‘Bluecrop’ (Vargas and Bryla, 2015). Soil
pH was slightly lower with granular fertilizers than with fertigation; however, leaf N was also
lower with granular fertilizer, whereas yield was greatest when plants were fertigated using
ammonium sulfate or urea sulfuric acid. The results indicate that blueberry is well suited to
fertigation. Larger applications of N fertilizer also increased plant growth in the study but did not
improve yield in any year, and was even detrimental to berry size during the first three years of
fruit production and to yield during the third year when granular fertilizers were applied.
Whether N was applied by fertigation or as granular fertilizer, only 65 to 90 lb N/acre per year
was required to optimize fruit production.
In addition to applying N solutions, a number of blueberry growers in the PNW (and elsewhere)
are incorporating humic acids (aka organic acids) into their fertigation programs. Humic acids
are complex mixtures of many acids produced by decomposition of organic matter. They are
present in soils, peat, coal, upland streams, lakes, and ocean water. Humic and fulvic acids
(lower molecular weight and higher oxygen content than other humic acids) are commonly used
as soil supplements and have been found to stimulate plant growth in a number of crops,
including blueberry. Root growth of ‘Draper’ was particularly enhanced by humic acids during
the first two years in a new planting (Vargas and Bryla, 2015). However, more work is needed to
determine if humic acids have any benefits on growth and fruit production in mature plants.
In organic production, we have successfully fertigated fish emulsion and used this product as the
sole nutrient source for eight years to date in a certified organic field. Fish emulsion generally
has about 4% N. The total amount of N in a gallon of fish is then 0.4 lb (one gallon weighs
about 10 lb). The total amount of N to apply (Table 4) was divided into 7 equal portions and
applied from mid-April (bloom) through mid-July every 2 weeks. Fish fertilizer also contains
significant amounts of P, K (Table 5) and Mg. When fertigating with organic products, it is
important to dilute the product so the viscosity is suited to fertigating. Also, pressurize the
system prior to injecting the fertilizer and run the irrigation after injection to ensure the system
flushes well. While we have had good success fertigating with fish emulsion for several years,
our research does show a reduction in emitter performance over time – this may be due to
accumulation of organic material from the fertilizer but could also have been caused by iron
bacteria. Good maintenance of a drip irrigation system is important for maintaining performance
over time.
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Acknowledgements
We appreciate the contributions of John Hart(retired) and Dan Sullivan, Dept. Crop and Soil Sci.,
OSU, Tim Righetti (formerly with OSU), Amanda Vance, Faculty Research Assistant, the
graduate students who have contributed to this body of work (Pilar Bañados, Denise Nemeth,
Handell Larco, and Oscar Vargas), and grower collaborators.
Additional resources
These publications, related to nutrient management, are available from the OSU Extension
Service at https://catalog.extension.oregonstate.edu/. Enter the publication number in the search
window to find easily.
Nutrient management for blueberries in Oregon. 2006. Hart, Strik, White, and Yang. EM 8918
Irrigation Water Quality Fertilizer Guide. 1998. Vomocil and Hart. FG 76
Managing Irrigation Water Quality for Crop Production in the Pacific Northwest. 2007.
Hopkins, Horneck, Stevens, Ellsworth, Sullivan. PNW 597
A Guide to Collecting Soil Samples for Farms and Gardens. 2013. Fery and Murphy. EC 628
Soil Test Interpretation Guide. 2011. Horneck, Sullivan, Owen and Hart. EC 1478
Soil fertility in organic systems. 2013. Collins, Miles, Cogger, and Koenig. PNW 646
Laboratories Serving Oregon: Soil, Water, Plant Tissue, and Feed Analysis. 2008. Hart. EM
8677
Soil Acidity in Oregon: Understanding and Using Concepts for Crop Production. 2013. Hart,
Sullivan, Anderson, Hulting, Horneck, Christensen. EM 9061
Acidifying Soil for Crop Production West of the Cascade Mountains (Western Oregon and
Washington). 2004. Horneck, Hart, Stevens, Petrie, and Altland. EM 8857
Acidifying Soil for Crop Production: Inland Pacific Northwest. 2007. Horneck, Wysocki,
Hopkins, Hart, Stevens. PNW 599
Acidifying Soil in Landscapes and Gardens East of the Cascades. 2006. Locke, Horneck, Hart,
Stevens. EC 1585
Applying Lime to Raise Soil pH for Crop Production (Western Oregon). 2013. Anderson, Hart,
Sullivan, Christensen, Horneck, Pirelli. EM 9057
Monitoring Soil Nutrients Using a Management Unit Approach. 2003. Staben, Ellsworth,
Sullivan, Horneck, Brown, Stevens. PNW 570
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Estimating Plant-Available Nitrogen from Manure. 2008. Sullivan. EM 8954
Estimating Plant-Available Nitrogen from Cover Crops, 2012. Sullivan and Andrews. PNW 636
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