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Nutrient Requirements, Leaf Tissue Standards, and New Options for Fertigation of Northern Highbush Blueberry

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Nutrient Requirements, Leaf Tissue Standards, and New Options for Fertigation of Northern Highbush Blueberry

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Northern highbush blueberry (Vaccinium corymbosum) is well adapted to acidic soils with low nutrient availability, but often requires regular applications of nitrogen (N) and other nutrients for profitable production. Typically, nutrients accumulate in the plant tissues following the same pattern as dry matter and are lost or removed by leaf senescence, pruning, fruit harvest, and root turnover. Leaf tissue testing is a useful tool for monitoring nutrient requirements in northern highbush blueberry, and standards for analysis have been updated for Oregon. Until recently, most commercial plantings of blueberry (Vaccinium sp.) were fertilized using granular fertilizers. However, many new fields are irrigated by drip and fertigated using liquid fertilizers. Suitable sources of liquid N fertilizer for blueberry include ammonium sulfate, ammonium thiosulfate, ammonium phosphate, urea, and urea sulfuric acid. Several growers are also applying humic acids to help improve root growth and are injecting sulfuric acid to reduce carbonates and bicarbonates in the irrigation water. Although only a single line of drip tubing is needed for adequate irrigation of northern highbush blueberry, two lines are often used to encourage a larger root system. The lines are often installed near the base of the plants initially and then repositioned 6-12 inches away once the root system develops. For better efficiency, N should be applied frequently by fertigation (e.g., weekly), beginning at budbreak, but discontinued at least 2 months before the end of the growing season. Applying N in late summer reduces flower bud development in northern highbush blueberry and may lead to late flushes of shoot growth vulnerable to freeze damage. The recommended N rates are higher for fertigation than for granular fertilizers during the first 2 years after planting but are similar to granular rates in the following years. More work is needed to develop fertigation programs for other nutrients and soil supplements in northern highbush blueberry. © 2015, American Society for Horticultural Science. All rights reserved.
Content may be subject to copyright.
Nutrient Requirements, Leaf Tissue Standards,
and New Options for Fertigation of Northern
Highbush Blueberry
David R. Bryla
1,3
and Bernadine C. Strik
2
ADDITIONAL INDEX WORDS.Vaccinium corymbosum, ammonium-nitrogen, fertilizer,
humic acids, organic, soil pH
SUMMARY. Northern highbush blueberry (Vaccinium corymbosum) is well adapted to
acidic soils with low nutrient availability, but often requires regular applications of
nitrogen (N) and other nutrients for profitable production. Typically, nutrients
accumulate in the plant tissues following the same pattern as dry matter and are lost
or removed by leaf senescence, pruning, fruit harvest, and root turnover. Leaf tissue
testing is a useful tool for monitoring nutrient requirements in northern highbush
blueberry, and standards for analysis have been updated for Oregon. Until recently,
most commercial plantings of blueberry (Vaccinium sp.) were fertilized using
granular fertilizers. However, many new fields are irrigated by drip and fertigated
using liquid fertilizers. Suitable sources of liquid N fertilizer for blueberry include
ammonium sulfate, ammonium thiosulfate, ammonium phosphate, urea, and urea
sulfuric acid. Several growers are also applying humic acids to help improve root
growth and are injecting sulfuric acid to reduce carbonates and bicarbonates in the
irrigation water. Although only a single line of drip tubing is needed for adequate
irrigation of northern highbush blueberry, two lines are often used to encourage
a larger root system. The lines are often installed near the base of the plants initially
and then repositioned 6–12 inches away once the root system develops. For better
efficiency, N should be applied frequently by fertigation (e.g., weekly), beginning at
budbreak, but discontinued at least 2 months before the end of the growing season.
Applying N in late summer reduces flower bud development in northern highbush
blueberry and may lead to late flushes of shoot growth vulnerable to freeze damage.
The recommended N rates are higher for fertigation than for granular fertilizers
during the first 2 years after planting but are similar to granular rates in the
following years. More work is needed to develop fertigation programs for other
nutrients and soil supplements in northern highbush blueberry.
Blueberry has lower nutrient re-
quirements than most crops
and thrives in acidic soils (pH
of 4.5–5.5) with limited availability of
essential nutrients such as nitrate-
nitrogen (NO
3
-N), phosphorus (P),
potassium (K), calcium (Ca), and mag-
nesium (Mg) (Korcak, 1988). How-
ever, despite the plant’s ability to
subsist with little to no fertilizer, a
good fertilization program is neces-
sary for rapid plant growth and high-
quality fruit production (Hanson and
Hancock, 1996; Hart et al., 2006).
Nitrogen is the primary nutrient ap-
plied to blueberry and is required
each year. Unlike most crops, blue-
berry acquires primarily the ammo-
nium (NH
4
) form of N over NO
3
-N,
due to low nitrate reductase activity in
the roots and leaves (Merhaut and
Darnell, 1995; Peterson et al., 1988).
When the plants are low in N, shoot
growth is poor, and the leaves turn
pale green or yellow (chlorotic) and
often develop a reddish tinge. Other
nutrients that are often applied to
blueberry include P, K, Ca, Mg,
elemental sulfur [S (which is used to
lower soil pH)], iron (Fe), boron (B),
copper (Cu), and zinc (Zn) (Hanson
and Hancock, 1996; Hart et al.,
2006). Manganese (Mn) is also re-
quired by the plants but is typically
available in abundance under acidic
soil conditions (Korcak, 1988). See
Caruso and Ramsdell (1995) for
useful illustrations of nutrient defi-
ciencies and toxicities in northern
highbush blueberry.
Traditionally, northern highbush
blueberry fields have been fertilized
using granular fertilizers. The current
recommendation for Oregon is to split
granular N fertilizers into thirds, with
the first application in late April, the
second in mid-May, and the third in
mid-June, at rates varying from 50 to
165 lb/acre N in plantings mulched
with sawdust, depending on the age of
the planting (Hart et al., 2006). These
recommendations are practiced by
northern highbush blueberry growers
throughout the United States and
elsewhere and are applicable to fields
irrigated by sprinklers. However, many
new fields are irrigated through drip
systems. In addition to using less
water, a major advantage of drip
irrigation is the ability to fertigate.
Units
To convert U.S. to SI,
multiply by U.S. unit SI unit
To convert SI to U.S.,
multiply by
0.4047 acre(s) ha 2.4711
0.3048 ft m 3.2808
0.0283 ft
3
m
3
35.3147
2.54 inch(es) cm 0.3937
0.4536 lb kg 2.2046
1.1209 lb/acre kgha
–1
0.8922
0.1198 lb/gal kgL
–1
8.3454
0.5000 lb/ton kgMg
–1
2.0000
1 micron(s) mm1
28.3495 oz g 0.0353
70.0532 oz/acre gha
–1
0.0143
31.2500 oz/ton gMg
–1
0.0320
2.2417 ton(s)/acre Mgha
–1
0.4461
(F – 32) O1.8 FC(C·1.8) + 32
This paper was part of the colloquium, ‘‘Recent
Advances in Perennial Berry Crop Nutrition and
Directions for Future Research,’’ held on 28 July
2014 at the ASHS Annual Conference in Orlando,
FL, and sponsored by the Viticulture and Small Fruit
Working Group.
We appreciate the funding support provided by the
Oregon and Washington Blueberry Commissions and
the Northwest Center for Small Fruits Research, and
thank Amanda Vance, Faculty Research Assistant, the
graduate students who have worked in northern
highbush blueberry nutrition (Oscar Vargas, Pilar
Ba~
nados, and Handell Larco), and our grower
collaborators.
Mention of trademark, proprietary product, or vendor
does not constitute a guarantee or warranty of the
product by the U.S. Department of Agriculture and
does not imply its approval to the exclusion of other
products or vendors that also may be suitable.
1
U.S. Department of Agriculture, Agricultural Re-
search Service, 3420 Northwest Orchard Avenue,
Corvallis, OR 97330
2
Department of Horticulture, Agricultural and Life
Science Building 4009, Oregon State University,
Corvallis, OR 97331
3
Corresponding author. E-mail: david.bryla@ars.usda.
gov.
464 August 2015 25(4)
Fertigation is the practice of applying
soluble fertilizers to the plants directly
through the irrigation system (Kafkafi
and Tarchitsky, 2011). Most of the
roots of a drip-irrigated plant are
located near the drip emitters, and,
therefore, nutrient application
through the drip system is a very
efficient way to apply the fertilizer
(Bryla, 2011). Several 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 spe-
cific 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. However, disadvan-
tages include the 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. System costs are even
higher when injection of corrosive ma-
terials such as sulfuric acid and acidified
fertilizers are needed(see‘Fertilizer
products available for fertigation’’).
Recently, Vargas and Bryla (2015)
compared the differences between fer-
tigation and granular fertilizer using
different sources of N fertilizer dur-
ing the first 5 years of fruit produc-
tion in ‘Bluecrop’ northern highbush
blueberry. 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 (Table 1). Ehret et al.
(2014) found similar results with
‘Duke’ northern highbush blueberry
in British Columbia and concluded
that fertigation produced greater
yields with less N than broadcast ap-
plications of the fertilizer. In both
cases, the results indicated that north-
ern highbush blueberry was well suited
to fertigation. Higher rates of N fer-
tilizer likewise increased plant growth
in both of these studies but did not
improve yield in any year and reduced
berry size during the first few years of
fruit production. Whether N was ap-
plied by fertigation or as granular
fertilizer, only 67–93 kgha
–1
Norless
was needed per year to optimize fruit
production.
The purpose of this article is to
review recent information on nutrient
requirements in northern highbush
blueberry and discuss the latest
options for fertigation by drip in
commercial production systems. The
article also contains updated stan-
dards for leaf tissue testing of north-
ern highbush blueberry that were
developed from a recent evaluation
of nutrients in common cultivars
growing in conventional and certified
organic fields in western Oregon.
Nutrient requirements
PLANT DEVELOPMENT.In most
cases, accumulation of nutrients in
each plant part follows the same pat-
tern as dry matter in northern high-
bush blueberry (Bryla et al., 2012).
Typically, the plants are propagated
from cuttings or by tissue culture and
transplanted to the field after 18
months in the nursery. Shoot growth
begins in the spring with bud swell
and is quickly followed by flowering.
The shoots grow in flushes, rapidly
producing 3–12 inches of new shoot
growth with each flush, depending on
shoot location and orientation; each
flush ends with apical bud abortion
(‘‘black tip’’ stage). Each shoot may
have one to several flushes of growth
during the season. New canes or whips
are the primary ‘‘renewal’’ wood for
subsequent fruit production and de-
velop throughout the season from the
base (crown) of the plants or from
latent buds from older wood higher
up on the bush. To improve establish-
ment of the plants, flower buds are
usually removed by pruning during
the first or second year after planting
to prevent competing sinks from fruit
production (Strik and Buller, 2005).
Depending on the cultivar and
growing region, the fruit require any-
where from 2 to 4 months to develop
and are usually harvested by hand or
machine over a period of 2–4 weeks.
Root growth has been shown to
peak before budbreak and after fruit
harvest (Abbott and Gough, 1987).
Most of the roots are very fine (40–
75 mmindiameter)andareoften
colonized by mycorrhizal fungi
(Valenzuela-Estrada et al., 2008).
The roots do not penetrate very
deeply and are usually confined to
the top 12–18 inches in most soils
(Bryla and Strik, 2007).
NUTRIENT UPTAKE AND LOSS.
Bryla et al. (2012) measured the
amount of nutrients accumulated and
lost in a new planting of ‘Bluecrop’
northern highbush blueberry (Table 2).
By the time the plants reached the first
fruit harvest in the second year after
planting, the plants acquired a total of
48.4, 3.1, 17.4, 12.0, 5.4, and 8.4
lb/acre of N, P, K, Ca, Mg, and S,
respectively; and 3.9, 0.6, 0.3, 17.6,
and 0.9 oz/acre of Fe, B, Cu, Mn,
and Zn, respectively. About 7% to
52% of each nutrient was lost or re-
moved from the planting through
leaf senescence, pruning, and fruit
harvest. Additional nutrients may
have been lost to root turnover
(Valenzuela-Estrada et al., 2008).
An estimated 70% of the N in the
plants at the end of the first year, and
25% of the N in the fruit the following
year, was derived from fertilizer ap-
plied initially during the spring after
planting (Ba~
nados et al., 2012). It is
likely that at least a portion of the P
and K acquired by the plants was also
Table 1. Comparison of granular and liquid nitrogen (N) fertilizers on soil pH,
leaf N, and yield of ‘Bluecrop’ northern highbush blueberry in western Oregon
(adapted from Vargas and Bryla, 2015).
Fertilizer
Soil Leaf N Yield
pH (%)
z
(tons/acre)
y
No fertilizer 6.2 a
x
1.29 d 15 c
Granular fertilizer
Ammonium sulfate 5.1 c 1.67 bc 22 b
Urea 5.6 b 1.60 c 24 ab
Fertigation
Ammonium sulfate 5.3 c 1.78 a 28 a
Urea 5.8 b 1.65 b 25 ab
Urea sulfuric acid 5.6 b 1.70 ab 27 a
z
Leaf N concentrations are considered normal at 1.76% to 2.00%, below normal at 1.50% to 1.75%, and deficient at
<1.50% (Hart et al., 2006).
y
Total cumulative yield during the first 5 years of fruit production (2008–12); 1 ton/acre = 2.2417 Mgha
–1
.
x
Means followed by a different letter within a column are significantly different at P£0.05, according to Tukey’s
honestly significant difference test.
August 2015 25(4) 465
derived from fertilizer, but no other
nutrients were applied to the planting.
The total amount of nutrients
removed during fruit harvest and
pruning were also measured recently
in mature plantings of northern high-
bush blueberry (B.C. Strik, unpub-
lished data). Nutrient removal in the
fruit differed among seven cultivars
and was very much dependent on the
yield (Table 3). The pruning losses
were measured in Elliott, which tends
to be a vigorous cultivar, often re-
quiring more pruning than many
others (Strik et al., 2014). Although
the wood removed during pruning is
usually flailed (chopped) between the
rows, the plants do not typically have
any roots between the rows. Hence,
any nutrients that recycle into the soil
after pruning are no longer available
to the plants. On the basis of the
estimated amount of nutrients con-
tained in the fruit and prunings, a ma-
ture field that produces an average
yield of 10 ton/acre will lose a total of
26–37 lb/acre N, 2.5–4.5 lb/acre P,
15–24 lb/acre K, 4–5 lb/acre Ca,
1.3–1.9 lb/acre Mg, 1.7–3.1 lb/acre S,
1.6–2.1 oz/acre Fe, 0.4–0.5 oz/acre B,
0.6–0.7 oz/acre Cu, 12.5–13.1 oz/
acre Mn, and 0.6–0.9 oz/acre Zn per
year. It is clear from these data that
the nutrient demands associated with
harvest and pruning are much lower
than the amount of fertilizer applied
to many plantings (Hanson and
Hancock, 1996; Hart et al., 2006;
Pritts and Hancock, 1992). Although
additional nutrients are required
for growth of new plant tissues and
to replace any losses in other dry
matter such as senesced leaves and
roots, more research is needed to
improve the efficiency of fertilizer
applications in northern highbush
blueberry.
LEAF NUTRIENT STANDARDS.Nu-
trient standards have been developed
for northern highbush blueberry us-
ing results from research experiments
and estimates from large databases
that relate tissue nutrient levels to
high-yielding fields (e.g., Hart et al.,
2006). The standards are based on
the analysis of the nutrients contained
in recent, fully expanded leaves on
shoots located below the fruiting
zone when collected in late July to
early August. Recently, tissue stan-
dards were reevaluated for western
Oregon using leaf nutrient concen-
trations obtained from mature plants
of six cultivars with different fruiting
seasons (B.C. Strik, unpublished
data). The cultivars included Duke,
which, at the location of the study,
ripens typically from mid-June to
early July; Draper, which ripens in
late June to mid-July; Bluecrop and
Legacy, which ripen throughout July;
Liberty, which ripens in mid to late
July; and Aurora, which ripens from
late July to late August (Strik et al.,
2014). Each cultivar was grown in
conventional and certified organic
fields. Regardless of the cultivar and
the fruiting season, best time to sam-
ple leaves for nutrient analysis was
confirmed as late July to early August.
However, there were significant dif-
ferences among cultivars during this
sampling period for many nutrients.
For example, concentrations of P,
K, Ca, and Cu in the leaves were
outside of the current recommenda-
tions (Hart et al., 2006). Although
the present recommendations are to
sample cultivars separately (Hart et al.,
2006), and this has been confirmed
(B.C. Strik, unpublished data), re-
vised standards will be developed to
account for broader variation among
the newer cultivars that may result
from differences in fruiting season
and nutrient allocation. A tissue stan-
dard will be developed for these nutri-
ents and will be added for aluminum
(Al). Although Al is not an essential
nutrient in northern highbush blue-
berry, low concentrations of Al in the
leaves may indicate that soil pH is too
Table 2. Accumulation and loss of nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), sulfur (S),
iron (Fe), boron (B), copper (Cu), manganese (Mn), and zinc (Zn) in a new planting of ‘Bluecrop’ northern highbush
blueberry in western Oregon (adapted from Bryla et al., 2012).
z
Activity period
Macronutrients (lb/acre)
y
Micronutrients (oz/acre)
y
N P K Ca Mg S Fe B Cu Mn Zn
Accumulation
Bud break to leaf senescence (year 1) 18.1 1.3 6.3 6.3 2.4 3.5 3.0 0.23 0.05 6.5 0.46
Bud break to harvest (year 2) 30.3 1.8 11.1 5.7 3.0 4.9 0.9 0.33 0.28 11.1 0.44
Losses
Leaf senescence (year 1) 8.3 0.4 4.2 2.7 0.6 1.5 1.5 0.14 <0.01 0.9 0.01
Winter pruning (year 1) 1.3 0.2 0.4 0.3 <0.1 0.1 0.3 0.01 <0.01 0.5 0.02
Fruit harvest (year 2) 9.0 0.5 4.6 0.3 0.3 0.4 0.2 0.05 0.02 0.2 0.04
z
Plants were fertilized each spring with 50 kgha
–1
N from granular ammonium sulfate.
y
1 lb/acre = 1.1209 kgha
–1
, 1 oz/acre = 70.0532 gha
–1
.
Table 3. Total amount of nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), sulfur (S), iron (Fe),
boron (B), copper (Cu), manganese (Mn), and zinc (Zn) removed during fruit harvest and winter pruning in a typical mature
planting of northern highbush blueberry in western Oregon.
z
Component
Macronutrients (lb)
y
Micronutrients (oz)
y
N P K Ca Mg S Fe B Cu Mn Zn
Fruit (per ton)
y
1.3–2.3 0.1–0.3 0.8–1.7 0.1–0.2 0.05–0.1 0.06–0.2 0.05–0.1 0.02–0.03 0.01–0.02 0.04–0.1 0.01–0.04
Prunings (per acre)
y
14 1.5 6.5 3.0 0.9 1.1 1.1 0.2 0.5 12.1 0.5
z
Ripe fruit were harvested for 2 years (2013–14) from seven cultivars, including Aurora, Bluecrop, Draper, Duke, Elliott, Legacy, and Liberty. The prunings were collected
from a mature planting of ‘Elliott’ northern highbush blueberry.
y
1 lb/ton = 0.5000 kgMg
–1
, 1 oz/ton = 31.2500 gMg
–1
, 1 lb/acre = 1.1209 tha
–1
, 1 oz/acre = 70.0532 gha
–1
.
466 August 2015 25(4)
COLLOQUIUM
high, and high concentrations often
indicate that pH is too low.
Fertilizer products available for
fertigation
NITROGEN SOURCES.As men-
tioned, blueberry requires primarily
the NH
4
form of N. Common sour-
ces of NH
4
or NH
4
-forming fertil-
izers available for fertigation include:
Ammonium nitrate solution
[NH
4
NO
3
H
2
O (20N–0P–0K)] or
AN-20 is commonly used for fertiga-
tion in many fruit and vegetable crops.
However, it is not recommended for
blueberry due to the high concentra-
tion of NO
3
-N (50% of total N) in the
solution.
Ammonium polyphosphate
[(NH
4
PO
3
)
n
(10N–34P–0K or 11N–
37P–0K)] contains 10% to 11% NH
4
-
N but is used primarily as a source
of phosphorus nutrition. Polyphos-
phate reverts quickly to monophos-
phate (only form of P taken up by
plants) in acidic environments and,
therefore, is readily available for up-
take by blueberry. It is widely used to
make a variety of fertilizer solutions.
The fertilizer forms highly insoluble
calcium pyrophosphates when injected
into irrigation water with high calcium
and high carbonate/bicarbonate con-
tents and, therefore, may severely plug
the drip emitters when used under
these conditions.
Ammonium sulfate [(NH
4
)
2
SO
4
]
is probably the most common
source of N applied to blueberry as
a granular fertilizer and is available in
the liquid form (8N–0P–0K–9S).
Solutions can be made using dry,
granular ammonium sulfate (21N–
0P–0K–24S), which dissolves in water
at a maximum solubility of 6.3 lb/gal
at 70 F.
Ammonium thiosulfate [(NH
4
)
2
S
2
O
3
(12N–0P–0K–26S)] is typically
used as an acidulating agent but could
also serve as potential N source for
blueberry plants growing in high pH
soils (>6.5). Although this product
has not been tested scientifically in
blueberry, several growers are cur-
rently using it for fertigation in com-
mercial northern highbush blueberry
fields in western United States (D.R.
Bryla, personal observations).
Calcium ammonium nitrate [Ca
(NO
3
)
2
NH
4
NO
3
(17N–0P–0K–
8.8Ca)] or CAN-17 is high in NO
3
-N,
low in NH
4
-N, and supplies calcium.
Certain crops such as strawberry
(Fragaria ·ananassa) and raspberry
(Rubus idaeus) appear to produce
higher quality fruit when fertilized
with CAN-17. However, like ammo-
nium nitrate solution, the fertilizer is
toohighinNO
3
-N for practical
application in blueberry.
Urea solution [(NH
2
)
2
CO (20N–
0P–0K or 23N–0P–0K)] is also com-
monly used for fertigation in northern
highbush blueberry, particularly when
soil pH <5.0. Urea rapidly converts to
NH
4
-N in the soil but is less acidifying
than ammonium fertilizers (Fig. 1). It
is also less costly per unit N and can be
made as a weaker dilution by mixing
granular urea [46N–0P–0K (another
fertilizer commonly used for granular
applications in blueberry)] in water at
a maximum solubility of 8.8 lb/gal
at 70 F. Note that the solution will
become extremely cold as the fertilizer
dissolves. Some growers are currently
combining urea and ammonium sul-
fate solutions to create a custom liquid
fertilizer blend (20N–0P–0K–5S) for
northern highbush blueberry.
Urea-ammonium nitrate solution
[(NH
2
)
2
CONH
4
NO
3
(32N–0P–0K)]
or UN-32 (UAN-32) is manufac-
tured by combining urea (46% N)
and ammonium nitrate (35% N).
Of the available N sources, urea-
ammonium nitrate has the highest
N concentration. It is marketed as
a 32% N solution in warmer agricul-
tural climates and as a 28% N solu-
tion in cooler agricultural areas.
Urea-ammonium nitrate solution
forms a thick, milky-white insoluble
precipitate when combined with
CAN-17 or other calcium nitrate
solutions, which could also cause
serious plugging problems.
Urea sulfuric acid [CO(NH
2
)
2
H
2
SO
4
] is an acidic combination of
urea and sulfuric acid. Mixing the
two products is extremely exother-
mic (explosive reaction if the temper-
ature is not controlled) and should not
be attempted under normal atmo-
spheric conditions. Combining the
two materials eliminates many of the
disadvantages of using them individu-
ally. The sulfuric acid decreases the
potential for volatilization losses from
the soil surface and ammonia damage
in the root zone, while including urea
with the sulfuric acid is much safer
than sulfuric acid alone. This product
is commonly sold under various
formulations of N and sulfuric acid
such as 10/55 (10% N and 55%
sulfuric acid), 15/49 (15% N and
49% sulfuric acid), and 28/27 (28%
N and 27% sulfuric acid).
For organic production, we suc-
cessfully fertigated a certified field of
northern highbush blueberry plants
with fish emulsion and used the prod-
uct as the sole nutrient source of
fertilizer for 8 years (B.C. Strik, un-
published data). The fertilizer was
particularly effective during establish-
ment and contained 4% N and sub-
stantial amounts of other nutrients,
including P, K, and Mg (Larco et al.,
2013a, 2013b). Several organically
approved liquid fertilizers are avail-
able for fertigation, including nonfish
products such as corn steep liquor;
these products mineralize rapidly
within a few weeks but vary consider-
ably in the cost per pound of actual N
applied (Mikkelsen and Hartz, 2008;
Miles et al., 2010). When fertigating
with organic fertilizers, dilute the
product before injection to lower
the viscosity, and flush the drip lines
at least annually to reduce emitter
plugging (Fernandez-Salvador et al.,
2015).
SOIL SUPPLEMENTS.In addition
to applying nutrient solutions, several
blueberry growers in the United States
and elsewhere are incorporating hu-
mic acids (also known as organic acids)
into their fertilizer programs. 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 several crops (Nardi et al., 2002;
Rose et al., 2014; Varaniniand Pinton,
Fig. 1. Average soil pH in a ‘Bluecrop’
northern highbush blueberry field
following 5 years of fertigation at
different nitrogen (N) rates with
ammonium sulfate or urea (adapted
from Vargas and Bryla, 2015); 1 lb/
acre =1.1209 kg
ha
L1
.
August 2015 25(4) 467
2001), including northern highbush
blueberry (Bryla and Vargas, 2014).
Reported benefits of these substances
include improved soil properties and
structure, greater bioavailability of soil
nutrients, increased microbial popula-
tions, and plant hormone-like effects
(Chen et al., 2004a, 2004b; Morard
et al., 2011; Muscolo et al., 2013;
Piccolo and Mbagwu, 1989). Root
growth was particularly enhanced by
humic acids during the first 2 years
after planting a new field of ‘Draper’
northern highbush blueberry (Fig. 2).
More work is underway in our group
to determine if humic acids are also
beneficial to growth and fruit produc-
tion in mature plants.
Injection of sulfuric acid (H
2
SO
4
)
into the irrigation water has also
become a popular practice in regions
with high soil pH and/or a high
percentage of carbonates (CO
3
)and
bicarbonates (HCO
3
) in the irrigation
water, such as California and eastern
Oregon and Washington. Because acid
materials are hazardous and highly
corrosive, several growers now use
sulfur dioxide (SO
2
) generators, often
referred to as ‘‘sulfur burners,’’ in place
of acid injectors for acidifying the
irrigation water and reducing soil pH.
Elemental sulfur burned in the gener-
ators is converted to sulfurous acid
(H
2
SO
3
) and mixed with the irrigation
water to lower the pH. Sulfur burners
are certified for organic production.
Other options for acidifying the water
in organic systems include injection of
acetic or citric acid.
Drip line placement
Although NO
3
-N is very mobile
and moves readily in moist soil to plant
roots, NH
4
-N moves much more
slowly, often advancing only 1–2 inches
over several months (Barber, 1995).
Therefore, the N in NH
4
fertilizers
will only be available to the plants
when the fertilizer is applied close to
the roots (Vargas et al., 2015). Any
of the fertilizer that is applied away
from the roots is likely to convert to
NO
3
-N, through a process of nitrifi-
cation, and eventually will be leached
from the field by rain or irrigation
(Haynes, 1990). On most soil types,
only one line of drip tubing per row
is needed for adequate irrigation of
northern highbush blueberry, but two
lines per row is often used to encour-
age a larger root system and increase
plant access to soil nutrients (Ehret
et al., 2012). The lines are often lo-
cated near the base of the plants during
the first or second year after planting
and later repositioned 6–12 inches on
each side of the plants as the root
system develops. Installing the drip
lines under weed mat or burying them
under sawdust mulch helps to secure
the lines in place, prevents any damage
during winter pruning, and reduces
water runoff on raised beds.
Since only a fraction of the soil is
wetted by the drip emitters, most of
the N applied to the plants during
fertigation is added directly to the
region of the soil where many of the
roots are concentrated. As a result,
extra N is not required with fertiga-
tion when sawdust or pine bark is
incorporated into the soil before
planting or used as mulch (Table 4).
This is in contrast to using granular
fertilizers, which requires an extra 25
lb/acre of N when 2–3 inches of fresh
sawdust is used as a mulch (Hart et al.,
2006).
Timing and rate of nitrogen
fertigation
Liquid fertilizers should be
injected in small and frequent appli-
cations (e.g., once per week), starting
at leaf emergence and finishing in late
July or early August. Fertigation is not
recommended for the entire growing
season (e.g., April–September) be-
cause N applications in late summer
reduce flower bud development in
northern highbush blueberry and
may lead to late flushes of growth
that increase the potential for freeze
damage over the winter (Caruso and
Ramsdell, 1995).
In western Oregon and Washing-
ton, many growers using drip irriga-
tion apply granular fertilizers in
March or April and then, once irri-
gation is required on a regular basis,
switch to fertigation in May (D.R.
Bryla, personal observations). The
use of granular fertilizer in the
spring is less expensive than fertiga-
tion and practical for use in mature
plants, provided weed mat (geotex-
tile fabric) is not used or is opened
before application. However, it may
cause fertilizer ‘‘burn’’ (salt damage
to shoots and roots from the fertil-
izer) in new plantings and, in severe
cases, can kill young plants (Ba~
nados
et al., 2012; Bryla and Machado,
Fig. 2. ‘Draper’ northern highbush
blueberry plants grown (A) with or (B)
without humic acids. The plants were
grown in a field in western Oregon and
destructively harvested following the
second year after planting (2012).
Shoot and root dry weight averaged
651 and 349 g, respectively, with
humic acids, and 561 and 246 g,
respectively, without humic acids; 1 g =
0.0353 oz (images courtesy of O.L.
Vargas).
Table 4. Effects of a preplant application of nitrogen (N) fertilizer on shoot and
root dry weight, leaf N concentration, and yield of ‘Draper’ northern highbush
blueberry in western Oregon.
z
Nitrogen fertilizer
incorporated into the
field before planting
y
Plant dry wt (g/plant)
x
Leaf
N (%)
w
Yield
(lb/plant)
v
Shoot Root
Yes 591 241 1.67 1.4
No 588 221 1.61 1.6
Difference
u
3
NS
20
NS
0.06
NS
0.2
NS
z
The plants were grown on raised beds with 19 units/acre of incorporated fresh sawdust (3.5 inches deep in 3-ft-
wide bands on 10-ft centers to a depth of 10 inches) and 11 units/acre (2 inches deep in 3-ft-wide bands on 10-ft
centers) of fresh sawdust mulch; 1 unit of sawdust = 200 ft
3
(5.6634 m
3
), 1 unit/acre = 2.4711 units/ha, 1 inch =
2.54 cm, 1 ft = 0.3048 m.
y
Granular ammonium sulfate was either incorporated along with the sawdust at a rate of 95 lb/acre (106.5 kgha
–1
)
N or was not incorporated at all before planting. Irrigation was applied using two lines of drip per row, and liquid
urea was injected (April–July) through the drip system at annual rate of 100 kgha
–1
(89.2 lb/acre) N per year.
x
The plants were destructively harvested in Oct. 2012, following the second year after planting; 1 g = 0.0353 oz.
w
Leaf samples were collected in early Aug. 2012, during the second year after planting.
v
Plants were lightly cropped during the second year after planting and harvested in July 2012; 1 lb = 0.4536 kg.
u
Difference between the means were compared by analysis of variance.
NS
Nonignificant (P>0.05).
468 August 2015 25(4)
COLLOQUIUM
2011). Even small applications of
granular ammonium sulfate ap-
plied at a rate of 20 kgha
–1
Nin
the spring, before fertigation, re-
duced shoot growth and caused
root damage in young ‘Draper’ plants
(Fig. 3).
The recommended N rates for
fertigation are shown in Table 5. The
rates are higher than those recom-
mended for granular fertilizers in
Oregon and British Columbia during
the first 2 years after planting but are
similar to the granular rates in the
following years (British Columbia
Ministry of Agriculture, 2014; Hart
et al., 2006). Higher N rates are
recommended initially for fertigation
due to low application efficiency in
young plantings (Bryla and Machado,
2011). Many growers using drip irri-
gation install drip tubing or drip tape
with in-line emitters spaced every 12
or 18 inches. Since the plants are usually
spaced 2.5–3 ft apart, roughly half of
the emitters end up between the plants
and outside of the root zone. Conse-
quently, much of the NH
4
-N is un-
available for a year or so, until which
time the root systems grow large
enough to reach the emitters between
the plants (Vargas et al., 2015). In
contrast, granular fertilizer is often ap-
plied by hand directly around the base
of plants (within the drip line of the
bush) during the first or second year
after planting (Hart et al., 2006).
By the third year after planting,
less N is needed with fertigation be-
cause most of the N at this point is
applied directly to the root zone and
is no longer lost between the plants
(Vargas et al., 2015). The N is also
injected in small and frequent appli-
cations during fertigation, which is
much more efficient than using two
or three large applications of granular
fertilizer. For example, Machado
et al. (2014) measured NH
4
-N in
the soil solution in a 3-year-old plant-
ing of ‘Bluecrop’ northern highbush
blueberry and found that concentra-
tions increased to 800–1500 ppm
following each of three applications
of granular ammonium sulfate, but
remained £10 ppm throughout the
season when the fertilizer was applied
once a week from mid-April to mid-
August by drip fertigation. Fertiga-
tion, in this case, also resulted in more
vegetative growth, greater yield, and
higher leaf N concentrations, and
therefore, was more efficient than
using the granular fertilizer, now that
the plants were larger.
Future directions for research
Avenues for future research on
nutrient management in blueberry
include fertigation with other nutri-
ents besides N and more work on soil
supplements such as humic and fulvic
acids. The information is needed to
identify the best sources of each nu-
trient and to determine the best time
and rate to apply them. The use of
humic and fulvic acids appears prom-
ising for blueberry, but the mecha-
nism(s) of their effect on root growth
and whether they increase fruit produc-
tion remains unclear. Possible mecha-
nisms include increased availability of
soil nutrients and chelation of micro-
nutrients, enhanced water pene-
tration and retention, stimulated
beneficial microbial activity, and in-
duced hormonal effects on root
growth. Research is also needed to
determine the implications of new
soil management practices such as
use of landscape fabric (weed mat)
for weed control on root growth
and root function and the effects it
might have on the availability of soil
nutrients.
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470 August 2015 25(4)
COLLOQUIUM
... In 'Legacy' northern highbush blueberry (NHB, Vaccinium corymbosum), HA application did not affect root growth, shoot growth, fruit yield, or fruit quality (Shoebitz et al., 2016;Shoebitz et al. 2019). In contrast, HA application promoted root growth in 'Draper' NHB (Bryla and Strik, 2015). Research focused on southern highbush blueberry (SHB, V. corymbosum interspecific hybrids) is unavailable. ...
... Young blueberry plants suffer water deficit stress for up to 3 weeks after transplant (Hicklenton et al., 2000), likely due to their small and spatially constrained root systems. Previous research suggests that HA applications promote root growth in some blueberry cultivars (Bryla and Strik, 2015). Thus, we hypothesized that HA applications could improve transplant success by enhancing root growth in 'Sweetcrisp' SHB. ...
... These results agree with previous findings in 'Legacy' NHB (Schoebitz et al., 2016) where HA application did not improve rooting or transplant success. However, our findings contrast with previous research where HA applications led to changes in root system size or architecture in 'Draper' NHB (Bryla and Strik, 2015), cucumber (Cucumis sativus) (Mora et al., 2012), and gerbera (Gerbera jamesonii) (Yazdani et al., 2014). It is possible that sustained HA applications lead to root architecture changes. ...
Article
Full-text available
Humic acids are a biostimulant that has captured the interest of blueberry growers, but information about humic acid use in blueberry is scarce. Blueberry plants suffer water deficit stress during transplant and photosynthetic limitations during fruit development. We hypothesized that humic acid applications improve transplant success and increase fruit yield and quality in southern highbush blueberry (SHB, Vaccinium corymbosum interspecific hybrids) grown in soilless substrates. We tested these hypotheses in two greenhouse experiments. First, we grew 'Sweetcrisp' SHB in rhizoboxes. Humic acids were applied via drench at concentrations of 0 mL⋅L − 1 , 7 mL⋅L − 1 , 13 mL⋅L − 1 , and 24 mL⋅L − 1 for 10 weeks. Humic acid application increased substrate respiration rates, pH, and electrical conductivity, but they did not increase root growth or improved transplant success. In a separate experiment, one year-old plants of 'Avanti', FL 09-311, and FL 06-19 SHB plants in 1.7 L pots were treated with 0 mL⋅L − 1 , 13 mL⋅L − 1 , and 24 mL⋅L − 1 humic acids during the fruit development period. Humic acid application did not increase yields and occasionally reduced fruit quality. While plant responses were genotype specific, these results suggest that humic acid applications are not beneficial during the transplant or fruit development periods in substrate-grown blueberry.
... In fact, when plants were treated with a high level of CaCl 2 , leaf Ca concentrations were above the normal range for highbush blueberry [4.1-8.0 mg·g À1 (Hart et al., 2006)]. Because blueberry is a calcifuge and is adapted to acidic soils with low Ca 21 concentrations, the plants tend to be efficient at Ca uptake and have relatively low requirements for the nutrient (Bryla and Strik, 2015). Thus, when a calcifuge plant such as blueberry is exposed to high concentrations of Ca 21 in the soil, they cannot regulate Ca 21 influx and consequently accumulate excessive amounts of the ion (Wacquant and Picard, 1992). ...
Article
Full-text available
Excess salinity is becoming a prevalent problem for production of highbush blueberry ( Vaccinium L. section Cyanococcus Gray), but information on how and when it affects the plants is needed. Two experiments, including one on the northern highbush ( Vaccinium corymbosum L.) cultivar, Bluecrop, and another on the southern highbush ( V. corymbosum interspecific hybrid) cultivar, Springhigh, were conducted to investigate their response to salinity and assess whether any suppression in growth was ion specific or due primarily to osmotic stress. In both cases, the plants were grown in soilless media (calcined clay) and fertigated using a complete nutrient solution containing four levels of salinity [none (control), low (0.7–1.3 mmol·d ⁻¹ ), medium (1.4–3.4 mmol·d ⁻¹ ), and high (2.8–6.7 mmol·d ⁻¹ )] from either NaCl or CaCl 2 . Drainage was minimized in each treatment except for periodic determination of electrical conductivity (EC) using the pour-through method, which, depending on the experiment, reached levels as high as 3.2 to 6.3 dS·m ⁻¹ with NaCl and 7.8 to 9.5 dS·m ⁻¹ with CaCl 2 . Total dry weight of the plants was negatively correlated to EC and, depending on source and duration of the salinity treatment, decreased linearly at a rate of 1.6 to 7.4 g·dS ⁻¹ ·m ⁻¹ in ‘Bluecrop’ and 0.4 to 12.5 g·dS ⁻¹ ·m ⁻¹ in ‘Springhigh’. Reductions in total dry weight were initially similar between the two salinity sources; however, by the end of the study, which occurred at 125 days in ‘Bluecrop’ and at 111 days in ‘Springhigh’, dry weight declined more so with NaCl than with CaCl 2 in each part of the plant, including in the leaves, stems, and roots. The percentage of root length colonized by mycorrhizal fungi also declined with increasing levels of salinity in Bluecrop and was lower in both cultivars when the plants were treated with NaCl than with CaCl 2 . However, leaf damage, which included tip burn and marginal necrosis, was greater with CaCl 2 than with NaCl. In general, CaCl 2 had no effect on uptake or concentration of Na in the plant tissues, whereas NaCl reduced Ca uptake in both cultivars and reduced the concentration of Ca in the leaves and stems of Bluecrop and in each part of the plant in Springhigh. Salinity from NaCl also resulted in higher concentrations of Cl and lower concentrations of K in the plant tissues than CaCl 2 in both cultivars. The concentration of other nutrients in the plants, including N, P, Mg, S, B, Cu, Fe, Mn, and Zn, was also affected by salinity, but in most cases, the response was similar between the two salts. These results point to ion-specific effects of different salts on the plants and indicate that source is an important consideration when managing salinity in highbush blueberry.
... Irrigation water can contain carbonates and bicarbonates (collectively called alkalinity). Alkaline water sources are not uncommon in blueberry production areas [38], but water acidification through sulfuric acid injection or sulfur dioxide generators is routinely used to neutralize alkalinity [39]. Our results suggest that increasing substrate pH buffering capacity can be beneficial for blueberry. ...
Article
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Blueberry (Vacciniumcorymbosum interspecific hybrids) production in soilless substrates is becoming increasingly popular. Soilless substrates have low pH buffering capacity. Blueberry plants preferentially take up ammonium, which acidifies the rhizosphere. Consequently, soilless substrates where blueberry plants are grown exhibit a tendency to get acidified over time. Agricultural lime (CaCO3) is commonly used to raise soil and substrate pH in other crops, but it is rarely used in blueberry cultivation. We hypothesized that substrate amendment with low rates of agricultural lime increases substrate pH buffering capacity and provides nutritional cations that can benefit blueberry plants. We tested this hypothesis in a greenhouse experiment with ‘Emerald’ southern highbush blueberry plants grown in rhizoboxes filled with a 3:1 mix of coconut coir and perlite. We found that substrate amendment with CaCO3 did not cause high pH stress. This amendment maintained substrate pH between 5.5 and 6.5 and provided Ca and Mg for plant uptake. When blueberry plants were grown in CaCO3-amended substrate and fertigated with low pH nutrient solution (pH 4.5), they exhibited greater biomass accumulation than plants grown in unamended substrates. These results suggest that low rates of CaCO3 could be useful for blueberry cultivation in soilless substrates.
... Alt et al. (2017) observed an increase in the assimilation of NO3in the roots, when NO3is supplied, suggesting that a large proportion of the NO3absorbed was assimilated within this organ. Bryla et al. (2015) found that the application of NH4 + + NO3 -, had intermediate nutritional levels in leaves, compared to the treatment where only NH4 + was added as N source. González et al. (2018) obtained an increase in the dry weight of bud, leaves, and root in blueberry plants, with the fertilization of N in the form of NH4 + , compared to plants fertilized with N-NO3 -. ...
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Blueberry (Vaccinium corymbosum L.) continues to gain importance in the international market due to its effects on the prevention of human diseases. This leads to the need to optimize the production and quality of the fruit. The present research evaluated the effect of NO3- and NH4+, using the split roots technique, in the nutritional status, photosynthetic pigments and total sugars in blueberry leaves. A completely random experiment was established with six greenhouse treatments: three under homogeneous root conduction (HR) and three with split roots (SR). The concentration of N, P, K, Ca, Mg, S, Fe, Cu, Zn, Mn, B and Na, chlorophyll a (Chl a), chlorophyll b (Chl b), carotenoids (Car) and total sugars were evaluated in the leaves. The exclusive supply of NH4+ led to the largest accumulation of N, P, Mg, S, Cu, Mn and B, compared to plants treated with NO3-. The Chla and total sugars were higher with NH4+ compared to NO3- nutrition. The supply of N separately (SR) had no positive effects on the evaluated variables, however, the SR with half of N, in the form of NH4+, compared to the non-SR with full application of N, has no differences in N-leaf concentration, which implies a higher use in the uptake or accumulation of this macro element in plant. V. corymbosum L. with split root and half of N in the form of NH4+, doubled the N use efficiency, as it matches in yield the complete supply treatment of N-NH4+ without root division.
... The plants were fertigated with liquid urea (20N-0P-0K) once every 2 weeks, from mid-April through the end of July each year, at rates recommended by Bryla and Strik (2015). The fertilizer was applied through the irrigation system using a fertilizer injector (Mix-Rite TF10-002; DEMA, St. Louis, MO) and 5 mm of water on each date. ...
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In many regions, water limitations are increasing because of frequent and persistent droughts and competition for water resources. As a result, growers in these regions, including those producing blueberries, must limit irrigation during drier years. To identify the most critical periods for irrigation, we evaluated the effects of soil water deficits during various stages of fruit development on different cultivars of northern highbush blueberry ( Vaccinium corymbosum L.). The study was conducted for 2 years in western Oregon and included two early season cultivars, ‘Earliblue’ and ‘Duke’, a midseason cultivar, ‘Bluecrop’, and two late-season cultivars, ‘Elliott’ and ‘Aurora’. Volumetric soil water content and stem water potentials declined within 1 to 2 weeks with no rain or irrigation in each cultivar and were lowest during the later stages of fruit development. Water deficits reduced berry weight by 10% to 15% in ‘Earliblue’ and ‘Elliott’ when irrigation was withheld in the second year during early or late stages of fruit development and by 6% to 9% in ‘Aurora’ when irrigation was withheld in either year during the final stages of fruit development. However, water deficits only reduced yield significantly in ‘Aurora’, which produced 0.8 to 0.9 kg/plant fewer fruit per year when irrigation was withheld during fruit coloring. In many cases, water deficits also reduced fruit firmness and increased the concentration of soluble solids in the berries, but they had inconsistent effects on titratable acidity and sugar-to-acid ratios. As a rule, water deficits were most detrimental during later stages of fruit development, particularly in midseason and late-season cultivars, which ripened in July and August during the warmest and driest months of the year.
... Many studies have suggested that ammonium is preferably taken up by blueberry plants, as compared to nitrate, probably due to an evolutionary mechanism derived from blueberry's adaptation to habitats characterized by acidic soils, in which ammonium is the most commonly available inorganic N ion (Cain, 1952;Brown, 1978;Korcak, 1988;Merhaut and Darnell, 1995;Merhaut and Darnell, 1996;Claussen and Lenz, 1999;Poonnachit and Darnell, 2004;Bryla and Strik, 2015;Nunez et al., 2015). However, it is not clear whether the better performance of blueberry plants at high NH 4 + concentrations is due to greater N uptake or to greater uptake of microelements, such as Fe, Mn or Zn, which are more available when the pH in the rhizosphere is low (Lindsay, 1979). ...
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The increased demand for blueberries and limited availability of low-pH soils have led to the increased use of soilless culture systems. The objective of this study was to evaluate the effect of a wide range of RNH4⁺ [RNH4⁺ = 100*N-NH4⁺/(N-NH4⁺+N-NO3⁻)] values on the acidification of the growth medium and the nutrient status and performance of blueberry plants. RNH4⁺ treatments of 25% (AN25, control), 50% (AN50) and 100% (AN100) and a 25% N-NH4⁺ plus concentrated sulfuric acid (AN25-acid) treatment were applied by fertigation to southern highbush blueberry plants (Vaccinium corymbosum, cv. Sunshine Blue) grown in a soilless substrate (50% tuff, 25% peat, 25% coconut coir). The original solution for the AN25-acid treatment was adjusted to a constant pH of 4.5. The pH and mineral concentrations in the leachate, pH of the growth medium and mineral and chlorophyll concentrations in the leaves were monitored periodically. Plant water uptake was monitored periodically and foliage volumes were calculated at the end of the growing season. Application of high levels of RNH4⁺ decreased the pH of the leachate and medium to below 5.5 and increased the concentrations of Fe, Mn and Zn in the leachate, as compared to the control treatment. Those treatments also increased the chlorophyll concentrations, total plant water uptake, foliage volumes and leaf Mn concentrations relative to the control treatment. The effects of the high-RNH4⁺ treatment on acidification and plant performance were not significantly different from the effects of the commonly used AN25-acid treatment. It seems, therefore, that the increased RNH4 reduced the pH of the growth medium to the required level for blueberry production, providing a safer and more environmentally friendly alternative to the use of sulfuric acid.
... Unlike most fruit crops, blueberry is well-adapted to low soil pH between 4.0 and 5.2, and low nutrient levels (Retamales and Hancock, 2012). However, the profitable production of high and quality berry yields requires regular, balanced and site-specific fertilization (Hanson, 2006;Bryla and Strik, 2015). ...
Article
The effect of silicon (Si) in the nutrient solution on the fruit development of 2-year-old blueberry plants (Vaccinium corymbosum L. cv. Ventura) was studied. Si was applied to the nutrient solution at a dose of 0.0, 0.6, and 1.2 mM. The parameters of fruit, stems and leaves growth, firmness, and biomass were measured. Fertigation in conjunction with traditional spread fertilization could improve the growth and yield of highbush blueberry to find the optimal method to control decay and prolong the quality of blueberries after harvest. The blueberry fruit has a light-blue appearance because its blue-black skin is covered with a waxy bloom. This layer is easily damaged or removed during fruit harvesting and postharvest handling. Si enhances the resistance of this layer to damage. A 2-year study was done to compare the effects of silicon fertigation and silicean sand and coir fiber as substrates on growth and availability of nutrients for blueberry plants during establishment of highbush blueberry (Vaccinium corymbosum L. “Bluecrop”). The results of experiment indicated that the application of Si had better benefit on the fruit growth of blueberry plants in coir fiber, than the effect that was observed in the sand substrate. The results should improve our understanding for better preservation of postharvest quality of blueberry fruit.
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A 2-year trial was established in Oct. 2016 in western Oregon to evaluate the effects of various in-row mulch treatments on establishment of northern highbush blueberry ( Vaccinium corymbosum L. ‘Duke’). The treatments included douglas fir [ Pseudotsuga menziesii (Mirb.) Franco] sawdust, black weed mat (woven polypropylene groundcover), green weed mat, and sawdust covered with black or green weed mat. For the most part, plant nutrient concentration and content were unaffected by the color of the weed mat. In both years, mulching with weed mat over sawdust reduced soil NO 3 -N compared with weed mat alone. The only other soil nutrient affected by mulch was K, which was highest with sawdust mulch and intermediate with black weed mat alone in year 2. There were inconsistent effects of mulch on leaf nutrient concentration during the study. In 2018, leaf N concentration was lowest with black weed mat over sawdust. There were few mulch effects on nutrient concentrations in senescent leaves in both years and in harvested fruit in year 2. Mulch had greater effect on nutrient concentration in dormant plant parts after the second growing season than after the first, with the addition of sawdust under weed mat leading to significant differences for many nutrients in various plant parts compared with weed mat alone. Total uptake of N ranged from 12 kg·ha ⁻¹ (black weed mat) to 17 kg·ha ⁻¹ (black weed mat over sawdust) in year 1 and averaged 33 kg·ha ⁻¹ in year 2, with no effect of mulch. Fertilizer use efficiency for N was 8% to 12% in year 1 and 42% in year 2. Uptake of other nutrients was unaffected by mulch and, depending on the year, ranged from 1.3 to 4.3 kg·ha ⁻¹ P, 4.0 to 8.0 kg·ha ⁻¹ K, 2.1 to 4.9 kg·ha ⁻¹ Ca, and 1.0 to 1.5 kg·ha ⁻¹ Mg. Each of these other nutrients was derived from the soil or decomposing roots.
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The effects of nitrogen (N) fertilizer application on plant growth, N uptake, and biomass and N allocation in highbush blueberry (Vaccinium corymbosum L. 'Bluecrop') were determined during the first 2 years of field establishment. Plants were either grown without N fertilizer after planting (0N) or were fertilized with 50, 100, or 150 kg·ha-1 of N (50N, 100N, 150N, respectively) per year using 15N-depleted ammonium sulfate the first year (2002) and non-labeled ammonium sulfate the second year (2003) and were destructively harvested on 11 dates from Mar. 2002 to Jan. 2004. Application of 50N produced the most growth and yield among the N fertilizer treatments, whereas application of 100N and 150N reduced total plant dry weight (DW) and relative uptake of N fertilizer and resulted in 17% to 55% plant mortality. By the end of the first growing season in Oct. 2002, plants fertilized with 50N, 100N, and 150N recovered 17%, 10%, and 3% of the total N applied, respectively. The top-to-root DW ratio was 1.2, 1.6, 2.1, and 1.5 or the 0N, 50N, 100N, and 150N treatments, respectively. By Feb. 2003, 0N plants gained 0.6 g/plant of N from soil and pre-plant N sources, whereas fertilized plants accumulated only 0.9 g/plant of N from these sources and took up an average of 1.4 g/plant of N from the fertilizer. In Year 2, total N and dry matter increased from harvest to dormancy in 0N plants but decreased in N-fertilized plants. Plants grown with 0N also allocated less biomass to leaves and fruit than fertilized plants and therefore lost less DW and N duringleaf abscission, pruning, and fruit harvest. Consequently, by Jan. 2004, there was little difference in DW between 0N and 50N treatments; however, as a result of lower N concentrations, 0N plants accumulated only 3.6 g/plant (9.6 kg·ha-1) of N, whereas plants fertilized with 50N accumulated 6.4 g/plant (17.8 kg·ha-1), 20% of which came from 15N fertilizer applied in 2002. Although fertilizer N applied in 2002 was diluted by nonlabeled N applications the next year, total N derived from the fertilizer (NDFF) almost doubled during the second season, before post-harvest losses brought it back to the starting point.
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A study was done to determine the macro- and micronutrient requirements of young northern highbush blueberry plants (Vaccinium corymbosum L. 'Bluecrop') during the first 2 years of establishment and to examine how these requirements were affected by the amount of nitrogen (N) fertilizer applied. The plants were spaced 1.2 × 3.0 m apart and fertilized with 0, 50, or 100 kg·ha-1 of N, 35 kg·ha-1 of phosphorus (P), and 66 kg·ha-1 of potassium (K) each spring. A light fruit crop was harvested during the second year after planting. Plants were excavated and parts sampled for complete nutrient analysis at six key stages of development, from leaf budbreak after planting to fruit harvest the next year. The concentration of several nutrients in the leaves, including N, P, calcium (Ca), sulfur (S), and manganese (Mn), increased with N fertilizer application, whereas leaf boron (B) concentration decreased. In most cases, the concentration of nutrients was within or above the range considered normal for mature blueberry plants, although leaf N was below normal in plants grown without fertilizer in Year 1, and leaf B was below normal in plants fertilized with 50 or 100 kg·ha-1 N in Year 2. Plants fertilized with 50 kg·ha-1 N were largest, producing 22% to 32% more dry weight (DW) the first season and 78% to 90% more DW the second season than unfertilized plants or plants fertilized with 100 kg·ha-1 N. Most DW accumulated in new shoots, leaves, and roots in both years as well as in fruit the second year. New shoot and leaf DW was much greater each year when plants were fertilized with 50 or 100 kg·ha-1 N, whereas root DW was only greater at fruit harvest and only when 50 kg·ha-1 N was applied. Application of 50 kg·ha-1 N also increased DW of woody stems by fruit harvest, but neither 50 nor 100 kg·ha-1 N had a significant effect on crown, flower, or fruit DW. Depending on treatment, plants lost 16% to 29% of total biomass at leaf abscission, 3% to 16% when pruned in winter, and 13% to 32% at fruit harvest. The content of most nutrients in the plant followed the same patterns of accumulation and loss as plant DW. However, unlike DW, magnesium (Mg), iron (Fe), and zinc (Zn) content in new shoots and leaves was similar among N treatments the first year, and N fertilizer increased N and S content in woody stems much earlier than it increased biomass of the stems. Likewise, N, P, S, and Zn content in the crown were greater at times when N fertilizer was applied, whereas K and Ca content were sometimes lower. Overall, plants fertilized with 50 kg·ha-1 N produced the most growth and, from planting to first fruit harvest, required 34.8 kg·ha-1 N, 2.3 kg·ha-1 P, 12.5 kg·ha-1 K, 8.4 kg·ha-1 Ca, 3.8 kg·ha-1 Mg, 5.9 kg·ha-1 S, 295 g·ha-1 Fe, 40 g·ha-1 B, 23 g·ha-1 copper (Cu), 1273 g·ha-1 Mn, and 65 g·ha-1 Zn. Thus, of the total amount of fertilizer applied over 2 years, only 21% of the N, 3% of the P, and 9% of the K were used by plants during establishment.
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The breakdown products of plant and animal remains, extracted in an alkaline solution, are commonly referred to as humic substances (HS). They can be extracted from a wide variety of sources, including subbituminous coals, lignites (brown coals), peat, soil, composts, and raw organic wastes. The application of HS to plants has the potential to improve plant growth, but the extent of plant-growth promotion is inconsistent and relatively unpredictable when compared to inorganic fertilizers. The goal of this review was to determine the magnitude and likelihood of plant-growth response to HS and to rank the factors contributing to positive growth promotion. These factors included the source of the HS, the environmental growing conditions, the type of plant being treated, and the manner of HS application. Literature reports of exogenously applied HS-plant interactions were collated and quantitatively analyzed using meta-analytic and regression tree techniques. Overall, random-effects meta-analysis estimated shoot dry weight increases of 22. ±. 4% and root dry weight increases of 21. ±. 6% in response to HS application. Nevertheless, actual responses varied considerably and were mainly influenced by the source of the HS applied, the rate of HS application, and to a lesser extent, plant type and growing conditions. HS from compost sources significantly outperformed lignite and peat-derived HS in terms of growth promotion, while HS application rate nonlinearly moderated the growth response under different circumstances. Our results demonstrate the difficulty in generalizing recommendations for the use of HS in agriculture; however, some specific suggestions for maximizing the efficacy of HS under certain conditions are offered. We also outline some recent developments in the use of HS as synergists for improving fertilizer use efficiency and the activity of microbial inoculants. Finally, we identify a number of research gaps, which, when addressed, should clarify how, when, and where HS can be best applied for the greatest benefit.
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The use of conventional drip and alternative micro irrigation systems were evaluated for 3 years in six newly planted cultivars (Earliblue, Duke, Draper, Bluecrop, Elliott, and Aurora) of northern highbush blueberry (Vaccinium corymbosum L.). The drip system included two lines of tubing on each side of the row with in-line drip emitters at every 0.45 m. The alternative systems included geotextile tape and microsprinklers. The geotextile tape was placed alongside the plants and dispersed water and nutrients over the entire length. Microsprinklers were installed between every other plant at a height of 1.2 m. Nitrogen was applied by fertigation at annual rates of 100 and 200 kg·ha-1 N by drip, 200 kg·ha-1 N by geotextile tape, and 280 kg·ha-1 N by microsprinklers. By the end of the first season, plant size, in terms of canopy cover, was greatest with geotextile tape, on average, and lowest with microsprinklers or drip at the lower N rate. The following year, canopy cover was similar with geotextile tape and drip at the higher N rate in each cultivar, and was lowest with microsprinklers in all but ‘Draper’. In most of the cultivars, geotextile tape and drip at the higher N rate resulted in greater leaf N concentrations than microsprinklers or drip at the lower N rate, particularly during the first year after planting. By the third year, yield averaged 3.1–9.1 t·ha-1 among the cultivars, but was similar with geotextile tape and drip at either N rate, and was only lower with microsprinklers. Overall, drip was more cost effective than geotextile tape, and fertigation with 100 kg·ha-1 N by drip was sufficient to maximize early fruit production in each cultivar. Microsprinklers were less effective by comparison and resulted in white salt deposits on the fruit. © 2015, American Society for Horticultural Science. All Right reserved.
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A systems trial was established in Oct. 2006 to evaluate management practices for organic production of northern highbush blueberry (Vaccinium corymbosum L.). The practices included: flat and raised planting beds; feather meal and fish emulsion fertilizer each applied at rates of 29 and 57 kg·ha-1 nitrogen (N); sawdust mulch, compost topped with sawdustmulch (compost + sawdust), or weedmat; and two cultivars, Duke and Liberty. Each treatment was irrigated by drip and weeds were controlled as needed. The planting was certified organic in 2008. After one growing season, allocation of biomass to the roots was greater when plants were grown on raised beds than on flat beds,mulched with organicmulch rather than a weed mat, and fertilized with the lower rate of N. Plants also allocated more biomass belowground when fertilized with feathermeal than with fish emulsion. Although fish emulsion improved growth relative to feather meal in the establishment year, this was not the case the next year when feather meal was applied earlier. After two seasons, total plant dry weight (DW) was generally greater on raised beds than on flat beds, but the difference varied depending on fertilizer and the type of mulch used. Shoots and leaves accounted for 60% to 77%of total plant biomass, whereas roots accounted for 7%to 19% and fruit accounted for 4% to 18%. Plants produced 33% higher yieldwhen grown on raised beds than on flat beds and had36%higher yield with weed mat thanwith sawdustmulch.Yield was also higherwhen plants were fertilized with the low rate of fish emulsion thanwith any other fertilizer treatment in 'Duke' but was unaffected by fertilizer source or rate in 'Liberty'.Although raised beds and sawdust or sawdust + compost produced the largest total plant DW, the greatest shoot growth and yield occurred when plants were mulched with weedmat or compost + sawdust on raised beds in both cultivars. The impact of these organic production practices on root development may affect the sustainability of these production systems over time, however, because plants with lower root-to-shoot ratios may be more sensitive to cultural or environmental stresses.
Article
A systems trial was established in Oct. 2006 to evaluate management practices for organic production of northern highbush blueberry (Vaccinium corymbosum L.). The practices included: flat and raised planting beds; feather meal and fish emulsion fertilizer each applied at rates of 29 and 57 kg·ha-1 nitrogen (N); sawdust mulch, compost topped with sawdust mulch (compost + sawdust), or weed mat; and two cultivars, Duke and Liberty. Each treatment was irrigated by drip and weeds were controlled as needed. The planting was certified organic in 2008. Bed type affected most leaf nutrients measured in one or both cultivars during the first year after planting, including N, phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), boron (B), manganese (Mn), and zinc (Zn), but had less of an effect on leaf nutrients and no effect on soil pH, organic matter, or soil nutrients measured the next year. Feather meal contained 12 timesmore Ca and seven times more B than fish emulsion and resulted in higher levels of soil Ca and soil and leaf B in both cultivars, whereas fish emulsion contained three times more P, 100 times more K, and 60 times more copper (Cu) and resulted in higher levels of soil P, K, and Cu as well as a higher level of leaf P and K. Fish emulsion also reduced soil pH. Compost + sawdustmulch increased soil pH and organic matter and resulted in higher levels of soil nitrate-N (NO3-N), P, K, Ca, B, Cu, and Zn than sawdust alone and increased leaf K and B. Weed mat, in contrast, resulted in the lowest soil pH and increased soil ammonium-N (NH4-N). Weedmat also reduced soil Ca and Mg, but its effects on leaf nutrients were variable. Leaf Ca, Mg, and B were below levels recommended for blueberry the first year after planting when plants were fertilized with fish emulsion, whereas leaf N was low or deficient on average in the second year when plants were fertilized with feather meal. Leaf B was also low the second year in all treatments, and leaf Cu was marginally low. Leaf K, conversely, increased from the previous year and was becoming marginally high with fish emulsion. Fish emulsion, weed mat, and compost were generally the most favorable practices in terms of plant and soil nutrition. However, given the impact of each on soil pH and/or plant and soil K, further investigation is needed to determine whether these practices are sustainable over the long term for both conventional and organic production of highbush blueberry.
Article
Rooted cuttings of blueberries ( Vaccinium corymbosum L.) were grown in nutrient solutions containing different levels and combinations of NH 4 -N and NO 3 -N. Disappearance rate of the two forms from the nutrient solutions as determined by periodic analysis indicated that the plants absorbed the NH 4 -N more rapidly than NO 3 -N. Although both forms produced healthy plants, the plants receiving NH 4 -N were twice the size and dry matter yield of the NO 3 plants after 15 weeks. Shoot N concentrations ranged from 0.99% to 1.29% for the N forms except where the blueberry plants had depleted the solutions of NH 4 -N before termination of the experiment. The N forms had a significant affect on the concentration of other plant nutrients, notably very low concentrations of Ca and Mg in roots with NH 4 -N and very high concentrations of Mn and Fe in roots with NO 3 -N plants. Expected levels of Mn and Fe and light brown roots were found with NH 4 -N plants.