CONTAINER NUTRITION MANAGEMENT PRACTICES
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Introduction
The goal of
a fertilization program is to apply the minimal amount of nutrients that result
in the desired growth rate, flower production, foliage color enhancement, or
expected plant quality. Minimal amounts of fertilizer needed to achieve the
desired response are impacted by container irrigation management practices that
were previously discussed, and the substrate, which is discussed below. Considering
these factors, nursery operators can develop a nutrient management plan and
achieve minimal fertilizer losses from containers.
Container Substrates
Many terms
including soil, media, soilless media, medium, potting or container mixes, and
substrates are used to describe potting materials for growing plants. However,
many of these terms are imprecise or can be confusing. Container mixes or
potting mixes imply that more than one component is used in potting and growing
plants. The term “substrate” avoids much of the confusion of other terms and is
descriptive of the entire composition. Substrate is the term used in Europe and
most other parts of the world to describe the components of the root rhizosphere within containers.
Many
materials are used as nursery container substrates. The predominant components
in the southeastern U.S. are pine bark, sand, and sphagnum peat moss.
Some
alternative materials that have been used include pine tree residuals,
composted hardwood bark, composted yard wastes and animal wastes, composted
biosolids, composted cotton gin wastes, municipal compost, rice hulls, wood
shavings, peanut hulls, and pecan shells. Substrates containing as much as
25-50% (by volume) compost are generally acceptable. The wetability, stability,
chemical, and physical characteristics may limit the portion of alternative
materials that can be used in a potting substrate. Unstabilized organic
components or components that have not been aged may decompose rapidly, leaving
a once full container three-fourth’s full in a few weeks or months. Some
composted materials lack the coarse large particles necessary for adequate
aeration and limit their use as a container substrate. Composted animal wastes
and mushroom compost characteristically have high salt levels, and therefore
are limited to 10 to 20% of the substrate volume.
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Container substrate components
should be selected for plants and management needs.
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Substrate components should be
stable and not decompose rapidly.
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Organic substrates should be free
of weed seed, nematodes, pathogens, and chemical contaminants.
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Substrates should be stored on
concrete slab where water never collects.
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Runoff from substrate storage
area should be contained or directed through vegetative filters if substrate is
amended with fertilizer.
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Areas surrounding substrate
storage should be kept mowed to prevent weed seeds from blowing onto the
substrate inventory. Sanitation is the first step toward a weed free nursery.
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Container Substrate Physical Properties
A container substrate is composed of solid,
gas, and liquid phases. For container substrates, these phases are usually
described in terms of physical characteristics such as bulk
density, air space, and container moisture capacity. Because
substrate physical characteristics dictate how much water and oxygen are
available to roots, they have a major impact on plant growth. Therefore, a
fundamental understanding of these physical characteristics is essential to
proper irrigation and fertilization management. The solid phase of a substrate
is described by the term “bulk density” which refers to the weight of substrate
per unit volume of substrate particles (g/cc oven dry weight). Bulk density
values for dry pine bark range from 0.19-0.24 g/cc (12.0 lbs/cubic ft - 15.0
lbs/cubic ft) depending on the particle size distribution of the pine bark.
Particle size distribution refers to sizes of particles (dust-like to chunks)
that compose a substrate. Because pine bark is porous, the volume of solids
composes a relatively low portion compared to volume of the gas and liquid
portions.
The particle
size distribution, particle density, and nesting of substrate component
particles greatly influence the gaseous and liquid characteristics of a substrate
(to be discussed). Many sizes of pine bark are available ranging from fine to
coarse; the size to be used is dependent on the type of crop and production
practices. Experience is usually the best judge of which to use. The gas phase
of a substrate is typically referred to as pore spaces. Pore spaces exist
between substrate particles and within particles and are a critical portion of
the substrate because these pores hold oxygen, which is essential for root
growth. The term “total porosity” refers to
the total volume of pore space in a substrate and is expressed as a percentage
of the total substrate volume. Recommended total porosity values range from
50-85%. The term “air space” refers to the
fraction of air-filled large pores (macropores) from which water drains
following irrigation. Air space values are also expressed as a percentage of
the total substrate volume and recommended values range from 10-30%.
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Peat moss, usually stored in
bales, is mixed with other components to formulate a container substrate.
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Pine bark should be stored on a
concrete slab and occasionally turned if stored for long durations.
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Depiction of solid, liquid, and
gas phases of a pine bark substrate
following irrigation and drainage (percent of
total substrate volume).
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The liquid
phase of a substrate is termed the substrate solution and is often
characterized by the term “container
capacity.” Container capacity is the maximum volume of water
that a substrate can retain following irrigation and drainage (water holding
capacity) due to gravity and is a measure of the water reservoir of a
container. Following irrigation and drainage, an area of saturation, called a
perched water table, exists at the bottom of a container. The height of the
saturated area is greater for a fine textured (small pores) substrate than for
a coarse textured (large pores) substrate. Above the perched
water table there is a gradient of air-filled pore spaces; the
amount of air-filled pores increase with the distance above the perched water
table.
Container
capacity is expressed on a volume basis as the percent of water retained
relative to the substrate volume. Recommended container capacity values range
from 45-65%. The water in a substrate can also be classified as “available” or
“unavailable.” Available water is that fraction of the water that can be
absorbed by roots. Unavailable water (hygroscopic water) is that fraction of
water that is held tightly to particles and is unavailable to roots.
Container
dimensions can affect air space and container capacity. For example, a typical
bark-filled 1-gallon container (six inches tall) might have a perched water
table that is one inch tall. Thus, the perched water table occupies 1/6 (17%)
of the container volume. Using the same bark, a flat (three inches tall) will
also have a one-inch perched water table; however, the water table will occupy
1/3 (33%) of the flat volume. Bilderback and Fonteno, 1987, discuss further
information on how container dimensions influences substrate characteristics.
The physical
properties of a substrate are also affected by amending the principle substrate
with another ingredient. Amending pine bark with sand increases the amount of
available water and bulk density; and decreases unavailable water, total
porosity, and air space. Adding peat moss to pine bark also increases the
amount of available water. The water in container must be balanced with air
space to prevent root rot; and conversely, the substrate should retain water to
minimize leaching. This delicate equilibrium can vary with plant species.
Recommended physical characteristic values for nursery container substrates
after irrigation and drainage are (percent volume): Total Porosity 50-85%; Air
Space 10-30%; Container Capacity 45-65%; Available Water Content 25-35% and
Unavailable Water Content 25-35%; and Bulk Density 0.19-0.70 g/cc. A substrate
with a high proportion of coarse particles has a high air space and a
relatively low water holding capacity. Consequently, leaching of pesticides and
nutrients is likely to occur.
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Air space refers to the
air-filled pores before irrigation (A) and after irrigation and drainage (B).
In general,
a substrate with a relatively
high proportion of micropores will have a high water holding capacity
due to the attraction of water
for the walls of small pores. Also, such a substrate will have a relatively
low total porosity value because
small particles tend to nest or settle within each other.
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Container A is filled with small
particles which fit together to form small pore
spaces while the large particles
used in container B form many larger pores.
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Moisture gradient in container substrate
at container capacity.
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Physical characteristics of
substrates should be tested and then used initially on a trial basis.
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Substrates should be used that
have recommended physical characteristics.
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Air Space and Water
Holding Capacity Measurements
A preferred
method of measuring these physical properties is presented in the Australian
Standards for Substrate Analysis (Standards Australian, 1989). Commercial
laboratories can conduct tests to determine these physical properties (see
Appendix B).
Handling Pine Bark
Inventories
Loblolly and
slash pine are the predominant species of pine grown and used for pine bark
substrates in the southeastern U.S. Pine bark is generally considered to be
non-phytotoxic and can be used without aging or composting but aging is
preferred because fresh pine bark often has less than 20-30% fine particles.
Fine particles less than 0.5 mm are generally considered responsible for
moisture retention in containers. Aging six to eight months produces a more
stable material and allows for the break down of larger particles, degradation
of wood, cambium, and complex
compounds associated with the turpentine-like smell of fresh pine bark. Aged
pine bark is sometimes referred to as composted bark. However, unless pine bark
is amended with a nitrogen source, moistened, and turned periodically true
composting does not occur.
Improper
handling of pine bark inventories during storage can result in detrimental
properties. Inventory windrows should be turned several times during aging and
moistened if dry. If windrows of inventory are stacked greater than eight feet
high or compacted by equipment, air exchange in windrows can be greatly reduced
resulting in an accumulation of alcohols or acetic
acid or both. Inventory windrows can reach temperatures of 180°F or higher. Steam rising from windrows indicates loss of
moisture. Dry areas may contain less than 34% moisture content by weight and
cannot be readily wetted. Plants potted from these areas may die due to
inadequate moisture retention. Areas below these dry areas may be anaerobic. Nursery personnel should check
the electrical conductivity and pH of these areas using a 2:1 water to bark
extraction. Electrical conductivity (soluble salts) of 2.5 mmhos/cm and pH
values below 3.5 has been reported. These conditions can cause death especially
for bare rooted transplants.
Pine bark in
unturned inventories may also develop high fungal populations marked by clouds
of spores when disturbed. If these inventories are used for potting, rapid
growth of mycelium may make wetting of
substrate in containers difficult and may result in crop losses. To avoid
problems related to inventory storage of pine bark, nursery personnel should
observe the condition of inventories at delivery and during storage. If
inventories are excessively hot and steamy or clouds of spores are observed,
moisten the new inventory, and check pH and electrical conductivity. If test
results exceed identified parameters, turn or mix inventory and moisten if
needed. Consider not using the inventory until test results are satisfactory.
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Pine bark should be checked for
moisture content, heat, spores, pH and electrical conductivity when turning
inventory windrows.
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Front end loaders can be used to
turn potting substrate inventories.
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Container Substrate
Chemical Characteristics
Cation Exchange
Capacity (CEC)
indicates how well a substrate holds positively charged ions (cations) such as
ammonium, potassium, calcium, and magnesium against leaching. Typical CEC
values (meq/100 ml) for several container substrate components are: aged pine
bark, 10.6; sphagnum peat moss, 11.9; vermiculite, 4.9; and sand, 0.5. The role
of CEC is minimal in soilless substrates as related to plant nutrient uptake
and leaching. Unlike a field soil, nutrients applied as a single application of
a soluble granular fertilizer leach rapidly from the container substrate.
Additionally, organic substrates have very little anion exchange capacity and
pH does not influence nutrient availability to the degree it does in a field
soil. The container system requires frequent irrigations because of the limited
water volume of the substrate, consequently, irrigation is a predominate factor
in controlling container substrate nutrient levels. Soluble fertilizers
injected frequently through the irrigation system or controlled-release
fertilizers should be used to provide a continuous supply of
nutrients at optimal levels, but in small enough quantities to minimize
nutrient loss due to leaching. Specific nutrient levels and pH required for
container substrates are discussed in section on Interpretation of Substrate
Extract Measurements.
Pre-Plant Fertilizer
Applications
The growth
substrate may be amended with dolomitic limestone and micronutrients prior to
planting as well as nitrogen, phosphorus, and potassium in the form of a
controlled-release fertilizer. Other amendments may include iron, sulfur,
gypsum, and magnesium.
Dolomitic Limestone
Dolomitic
limestone supplies Ca and Mg and neutralizes the acidity
of the growth substrate. The quantity of dolomitic limestone added to the
substrate depends on irrigation water alkalinity and Ca and Mg content, initial
pH of growth substrate, and the plant species grown. Hollies, loropetalums, and
ericaceous plants (e.g. azaleas) grow best in acid substrates, pH 4.5-5.5 and
may not require limestone additions. Nandina, junipers, boxwood and many other
plants including flowering shrubs, require a substrate pH of 5.5-6.5. Several
species of trees have grown well without the addition of dolomitic limestone in
pine bark substrates as long as the substrate pH was acidic and micronutrients
were added. Dolomitic limestone (75% passing through a 100-mesh sieve and
containing a minimum of 6% Mg) amendments of 4-6 pounds per cubic yard are
sufficient to meet the needs of most plants requiring limestone additions.
Limestone amendments may be effective for up to two growing seasons depending on
limestone particle sizes and hardness. A dolomitic limestone amendment is
usually not needed if the irrigation water has an alkalinity or hardness above
100 ppm and contains Ca and Mg concentrations above 40 and 20 ppm,
respectively.
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When dolomitic limestone is
needed, 4-6 pounds per cubic yard should be used for most plants.
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Micronutrients
Micronutrients
are essential for plant growth, but only a small quantity is required. There
are several micronutrient fertilizers sold commercially. These fertilizers
usually contain the essential micronutrients and are added to the container
substrate as an amendment. Micronutrient amendments can be effective for up to
two growing seasons unless irrigation water alkalinity is high, in which case
additional applications of micronutrients may be needed. Micronutrients are
available as components in controlled-release fertilizers. Preliminary studies
with container-grown shrubs (hollies, azaleas) and tree seedlings (pin oak,
Japanese maple) indicate that controlled release fertilizers with
micronutrients are effective in supplying micronutrients without the addition
of micronutrient amendments. If composted yard debris, composted hardwood bark,
or composted biosolids are 10% or greater by volume of the substrate, then
micronutrient needs may be met by these components.
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Micronutrient amendments should
be applied according to manufacturer’s recommendations listed on the product
label.
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Iron sulfate
is commonly added to pine bark substrates in areas where water alkalinity is
high to provide sufficient iron to prevent chlorosis and to help slow the
process of substrate pH increasing. Iron sulfate additions of up to 1.5 pounds
per cubic yard in pine bark substrates can be used to reduce substrate pH for
two to three months. Iron chelates are rarely used as amendments.
Macronutrients
Phosphorus
leaches rapidly from soilless container substrates. Complete controlled-release
fertilizers applied during the growing season should supply adequate
phosphorus.
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Superphosphate should not be
added to the container substrate.
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Granular
sulfur can be used to maintain an acidic pH in container substrates when
problems occur with increasing pH during the production cycle. Granular sulfur
will react slower than fine sulfur with a response being evident in three
months. Begin by testing a granular sulfur product at the rate of 0.25 pounds
per cubic yard and monitor substrate pH.
Gypsum
(calcium sulfate) is used to provide calcium and sulfate-sulfur without
increasing the pH of the substrate. Rates of 0.5-2.0 pounds of gypsum per cubic
yard of substrate have been used effectively.
Magnesium
deficiency can be a problem due to 1) the greater solubility of magnesium
carbonate in dolomitic limestone compared to calcium carbonate, or 2) areas
where there is an imbalance of calcium to magnesium in irrigation water. Magnesium
sulfate can be used as an amendment to provide magnesium and sulfate-sulfur.
However, magnesium sulfate is readily soluble and soon leaches from the
container. Kieserite is another soluble form of magnesium that has a release
period about twice that of magnesium sulfate. Several combination products of
magnesium oxide and magnesium sulfate are available that provide a longer
period of release. Magnesium oxide should be used with caution because the
release rate is correlated with particle size (larger the particle, slower
release) and it has the greatest potential to increase substrate pH (2.5 times
greater than dolomitic limestone). Amendments of controlled-release magnesium
products can be used. Controlled-release fertilizers with 1% magnesium have
reduced or eliminated symptoms of magnesium deficiency.
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Fertilizer should be mixed with substrate or subsurface applied at planting according to manufacturer’s recommendation.
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Care should be taken to ensure the coating or covering on the fertilizer granules is not cracked or broken in the process of mixing fertilizer with the substrate.
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Substrates amended with fertilizers should be placed in containers within a few days to prevent salt buildup caused by high bulk substrate temperatures.
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Post-Plant Fertilizer
Applications
One or more
applications of a controlled-release fertilizer applied to substrate surface or
a solution fertilizer applied through the irrigation system are often used to
accomplish fertilization during production.
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Fertilizer should be applied based upon plant
need. This may vary with plant species and time of year. A fertilizer nutrient
ratio of approximately 3:1:2, N:P205:K20 is
preferred.
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Controlled-Release Fertilizer
(CRF)
Controlled-release
fertilizers supply essential plant nutrients for an extended period of time
(months). Fertilizers are available that contain different mechanisms of
nutrient release and contain different nutrients. Care must be taken to select
the correct fertilizer for your specific purpose and geographic location. Because
nutrient release from most products is primarily controlled by temperature,
product selection would be different in warmer southern states compared to more
northern Mid-Atlantic States.
Controlled-release
fertilizer application rates will vary with product but will also depend on
species and container size. The goal of a fertilization program is to apply the
least amount of fertilizer for the desired growth so that nutrient leaching is
minimal. Excessive irrigation may reduce the effectiveness of CRF fertilizers
due to leaching of nutrients from container.
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Controlled-release fertilizers should be
uniformly mixed into the substrate prior to potting. This practice may be more
economical than surface application after planting.
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Controlled-release fertilizers
should be applied at manufacturer’s recommended rates. Reapplication of a
fertilizer occurs when substrate solution nutrient status is below desirable
levels (see section on Monitor Container Substrate Nutrient Status).
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Application rates used in fall
and winter (after first frost), should be one half the rates used in summer for
the same type of production.
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Fertilizer should not be broadcast
on spaced containers.
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Fertilizer in Irrigation Water
Another
method is to apply a fertilizer solution through the irrigation system with the
frequency of application and/or fertilizer concentration in the irrigation
water dependent on nutrient concentration in the container substrate solution.
CAUTION: when fertilizer is injected in the overhead irrigation system you will
need to take steps to address the nutrient loading of the water leaving your
property, because much of the water from overhead irrigation systems falls
between containers. Fertilizing through the irrigation water is less of a
concern for microirrigation systems in which irrigation water is delivered into
the container. Even then, care should be taken to minimize leaching from the container
to prevent nutrient laden runoff from entering surface or groundwater.
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Runoff should be collected or steps taken to
reduce nutrient levels in runoff water before water leaves the property if
fertilizer was in overhead irrigation water. Collecting and recycling of runoff
water is an appropriate and effective solution.
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Supplemental Fertilization
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Supplemental fertilizer should be
applied based on regular monitoring of EC levels in container substrate (see
below) so desired nutritional levels are maintained.
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Individual elements or a
combination of elements should be injected in concentrations slightly less than
desirable levels maintained in the growth substrate (Table 6).
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Surface-applied fertilizer should
be applied to small blocks or groups of plants, thus minimizing nutrient loss
and nutrient loading of runoff water.
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Apply controlled-release
fertilizer uniformly with a spoon, drop-tube, or metering devise.
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Plants should be grouped
according to their fertilizer needs so supplemental fertilizer applications are
made only to plants requiring additional fertilizer (Table 7). This is
particularly important when fertilizer is injected in irrigation water.
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Broadcast fertilizer applications
should be avoided unless containers are placed beside each other.
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Record of Fertilizer
Application
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Keep accurate fertilization
application records (as outlined in Table 5). This should include application
rate (including supplemental applications) for each plant type and container
size in addition to other important information (Table 5). This information may
prove very valuable to document that you have followed recommended fertilizer
management practices and as a valuable source of information in case plant
abnormalities develop that may be attributed to fertilizer application.
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Monitor Container Substrate
Nutrient Status
Environmental
conditions influence the longevity of fertilizer release. Thus, to ensure
adequate nutrient levels in the growth substrate, nursery operators should
monitor container substrate nutrient status and use results to determine
fertilizer reapplication frequency and rate, ensuring that desired levels are
maintained. Periodic monitoring is important because excessive or inadequate
nutritional levels may not be expressed by visual symptoms, although growth is
reduced. High concentrations of nutrients can result from substrate components,
inadequate irrigation frequency and duration, water source, and/or fertilizer
materials and application methods. Container substrate nutritional levels may
also rise during the over wintering of plants in polyhouses. Excessive nutrient
concentrations injure roots, ultimately restricting water and nutrient uptake. Conversely,
rainfall and excessive irrigation can leach nutrients from the container
substrate resulting in inadequate nutritional levels and threaten water
quality.
How Often to
Monitor
Substrates
used for long-term crops should be tested at least monthly, but biweekly
monitoring during the summer may be necessary to track fluctuations in
electrical conductivity (EC) which is used as a relative indicator of the
nutritional status of the container substrate. Even when controlled-release
fertilizers are used, substrate nutritional levels will gradually fall during
the growing season to levels that may not support optimal growth. Care must be
taken to monitor substrate EC to ensure that adequate nutrients are available
for plant growth but also to ensure that containers do not have excessive
levels of nutrients. It is advisable to monitor EC (salt levels) in containers
about one week after planting to ensure that high levels of salts are not
present due to fertilizer. Excessive fertilizer salt levels can also develop in
substrates due to high temperature during decomposition.
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Fertilizers are surface-applied
to small group of plants.
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Table 5. Fertilizer application record sheet.
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Date
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Field
Location
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Fertilizer/
Longevity Analysis
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Brand
Name
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Amount
Applied*
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Application
Frequency*
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Plant
Name
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Container
Size
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Env't'l.
Condition
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Area (acres)
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Table 6. Maintain these desirable nutritional levels in the container
substrate for plants with medium to high nutritional requirements. Levels are
for interpretation of the Pour-through (PT) and Suction Lysimeter (SL) when
fertilizing with solution or liquid fertilizer alone or in combination with
controlled-release fertilizers (CRF) or using only controlled-release
fertilizer.
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Analysis
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Desirable
levels
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Solution only or CRF and solution
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CRF fertilizer only
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pH
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4.5 to 6.5
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4.5 to 6.5
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Electrical conductivity,
mmhos/cm (dS/m)
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0.8 to 1.5
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0.5 to 1.0
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Nitrate-N, N03-N
mg/L (ppm)
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50 to 100
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15 to 25
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Phosphorus, P
mg/L
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10 to 15
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5 to 10
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Potassium, K
mg/L
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30 to 50
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10 to 20
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Calcium, Ca mg/L
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20 to 40
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20 to 40
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Magnesium, Mg
mg/L
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15 to 20
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15 to 20
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Manganese, Mn
mg/L
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0.3
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0.3
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Iron, Fe mg/L
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0.5
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0.5
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Zinc, Zn mg/L
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0.2
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0.2
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Copper, Cu mg/L
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0.02
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0.02
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Boron, B mg/L
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0.05
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0.05
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Levels
should not drop below these during periods of active growth. Plants with low
nutritional requirements
may grow
adequately with lower nutrient levels. See Table
7 for plants with a low nutritional requirement.
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During the growing season,
container substrates should be monitored every two to four weeks.
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High
temperatures in overwintering structures can result in nutrient release from
controlled-release fertilizers. Monitor substrate electrical conductivity two
or three times during the winter to ensure levels are not toxic.
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Substrate electrical conductivity
should be monitored two or three times during the winter months.
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Substrate Monitoring
Considerations
Nutrients
may accumulate in specific locations in substrate due to irrigation patterns
and fertilization methods. Therefore, one isolated sample will not give an
accurate representation of the nutrient status of the substrate. Collect
several (3-4) representative substrate samples to ensure that samples represent
the growth substrate being considered.
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Substrate Sampling Methods for
Nutrient Extraction
Several
procedures have been used to extract the nutrient solution from the container
substrate for nutritional analyses. The Pour-through
(PT) or leachate collection method
enables rapid sample collection from containers that are easy to lift. For
larger or heavier containers (for example #15 or #25) a modification of the
Pour-through using suction lysimeters (SL) is
recommended. The PT and SL are simple, nondestructive procedures that are easy
for nursery operators to perform. PT and SL methods are described in detail in Appendix C. These methods of nutrient
solution extraction allow nursery operators to make quick determinations of
substrate electrical conductivity and pH. For additional analyses, samples can
be sent to a laboratory (see Appendix A) for determination
of elemental concentrations. All laboratories do not use the same procedures so
test results can differ between laboratories. Consequently, interpretation of
results is very important.
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Container substrate solution extraction for
small containers is accomplished with the Pour-through.
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A Suction Lysimeter remains in
the large container for repetitive sampling of the container solution.
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The Pour-through (PT) and
Suction Lysimeter (SL) for Monitoring Nutrients in Container Substrates
General
Considerations
Container
plants should be irrigated using your normal practices one to two hours before
monitoring nutrients. For accurate and
comparable monitoring events, containers should be at or near container capacity
(excess water has drained from container). Monitoring should be performed on
containers (usually 3-5) that are representative of a particular species, or
irrigation or fertilization regimes.
Small Containers
After
irrigation and excess water drains from container, place each test plant over a
collection reservoir that will catch drainage from all holes. The bottom of the
container should be elevated above the collection reservoir so bottom of
container does not contact leachate or extract that drains. Apply sufficient
distilled water (tap water is fine if of reasonable quality) in a circular
motion to the surface of container substrate so that about 50 ml (1.5 oz) of
leachate or extract is collected. Table
8 provides approximate volumes to apply to containers of different
sizes.
Collect all
the leachate from each container. The amount collected will vary but should not
affect pH or EC readings. Usually collecting 50 ml is sufficient. Applying an
excessive volume of water to a container can result in low EC readings. It is
important to keep leachate from contacting bottom of container because salts
that precipitated and accumulated on or around the holes of container could
influence solution salinity, resulting in erroneous EC readings.
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The container must be elevated to
avoid contamination of the leachate.
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Lysimeter composed of hollow tube
(2 ft x 2 in) with porous ceramic cup at bottom.
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Large Containers
It is very
difficult to lift large containers and find sufficiently large collection
reservoirs so suction lysimeters can be used to extract the substrate solution
from these containers. The lysimeter consists of a porous ceramic cup attached
to the bottom of tube. Lysimeters can be purchased from SoilMoisture Equipment
Corp., P.O. Box 30025, Santa Barbara, CA 03105: http://www.soilmoisture.com. Model 1900 L24
with a one-half-bar air-entry value, vacuum pump 2005G2, and 1000K2 extraction
kit are recommended. Other vacuum pumps and extraction methods are also
acceptable.
It is
recommended that lysimeters be installed for duration of production. Make a
pilot hole, approximately one half the diameter of the lysimeter and vertically
through the substrate to the bottom of the container. A two-foot-long length of
a one inch metal bar is adequate for this purpose. The difference in diameter
between the pilot hole and the lysimeter ensures a tight fit between the
substrate and the lysimeter.
One to two
hours following irrigation, a vacuum pump is used to extract water from the
container through the ceramic cup and into the lysimeter. The vacuum should not
exceed 50 cbar. Immediately seal the lysimeter port to maintain the vacuum. After
5-15 minutes, about 50 ml of solution or extract will be in bottom of the
lysimeter. Open the top of lysimeter (you may hear the release of the remaining
vacuum) and draw out the solution with a syringe.
The solution
collected can be analyzed for EC, pH, or complete nutrient analysis. Three or
four lysimeters should be installed within a block of plants of the same
species, irrigation regime, or fertilization regime.
Interpretation of Substrate Extract
Measurements
Interpreting
the EC and pH readings may require some practice and a season-to-season
knowledge of the crops in question.
These measurements are often sensitive to changes in cultural
conditions, including changes in fertilization and watering practices, and to
changes in temperature, precipitation, and water quality. For these reasons, it
is important to maintain consistency in the extraction method and the
conditions in which used. However, repeated measurement of EC and pH over time
has allowed us to make some general recommendations based on potential
availabilities or toxicities of nutrients at different pH values, and on
relationships between EC and nutrients in extract solution.
It is
important to calibrate the pH and EC meters just prior to use. Use
manufacturers’ recommended standards and make sure they are not outdated. Follow
manufacturers’ instructions for calibrations and other determinations.
The pH and
EC determinations for each substrate liquid extract should be completed within
one to two hours after sampling. Record
your results along with cultural information about plants tested. Cultural
information, such as irrigation and fertilization regimes, can be very helpful
for making management decisions in the future.
Electrical
Conductivity
Most
fertilizers (except urea) are salts and when fertilizers are in solution they
conduct electricity. Thus, the electrical conductivity of a substrate solution
is indicative of the fertilizer level that is available to plant roots. Container substrate nutritional levels in Table 6 may be compared to those
obtained from plants sampled with the PT or SL methods of extraction. If
nutritional levels that result from application of controlled-release
fertilizers should drop below desirable levels during periods of active plant
growth, then reapplication should be considered to maintain optimal levels in
the substrate. Application of fertilizer through the irrigation system may also
be adjusted to compensate for either too high or too low EC readings.
|
Low EC
values may indicate over-irrigation and excessive leaching of nutrients,
periods of minimal release of controlled-release fertilizer, or improper
calibration of a fertilizer injector. Values considerably higher than those
suggested; may indicate a poorly calibrated injector, over-application of
granular or controlled-release fertilizer, improper release of
controlled-release fertilizer, or under-irrigation and excessive accumulation
of salts. Research-based knowledge of the appropriate nutrient levels for
optimal plant growth is limited and there is no substitute for experience.
|
Lysimeter positioned in
container.
|
Container substrate electrical
conductivity levels should be maintained between 0.8-1.5 mmhos/cm for plants
fertilized with solution fertilizer only or with the combined use of
controlled-release and solution fertilizer. Container substrate electrical
conductivity levels should be maintained between 0.5-1.0 mmhos/cm for plants
fertilized with controlled-release fertilizer only. These ranges (see Table 6)
are applicable to most container-grown landscape plants.
|
Plants with
a low nutrient requirement (Table 7)
may grow adequately with nutrient levels lower than those given in Table 6. Many herbaceous annual and
perennial plants have higher nutritional requirements. Recent research suggests
that EC measurements of 1.0-2.5 mmhos/cm may correspond to adequate nutrition
for these plants. Particular adjustments must be made for plants known to be
sensitive to fertilizer additions.
|
Irrigation water electrical
conductivity should be determined. The irrigation water electrical conductivity
enables you to know the contribution of your water to the solution extract
electrical conductivity and this should be considered when interpreting the
substrate electrical conductivity.
|
pH
Substrate
solution pH may impact nutrient availability. The recommended solution pH
varies with different crops, but a range between 4.5 and 6.5 is considered
adequate for most crops grown in pine bark-based substrate. Fertilizer formulations may affect substrate
solution pH. Gradual increases or decreases in pH throughout production should
be noted and referred to a plant nutrition specialist if pH exceeds the
recommended range for your crops.
Excessively
high or low irrigation water pH values may indicate problems with water quality
and the need to use substrate amendments to align substrate solutions with
recommended nutrient ranges for optimal plant growth. A reputable water-testing
lab can conduct a complete irrigation water analysis.
|
pH of substrate and irrigation
water should be determined as per container substrate monitoring schedule.
|
The substrate extract solution is
tested for soluble salts using an electrical conductivity (EC) meter.
|
Table 7. A partial list of container-grown plants with their nutritional
requirements is given below. Plant Requirements will vary depending on growth
rate desired and cultural conditions.
|
Scientific
name
|
Common
name
|
Nutrient
Requirement
|
Abelia x grandiflora
|
Glossy
Abelia
|
medium
|
Acca sellowiana
|
Pineapple
Guava
|
medium
|
Acer palmatum
|
Japanese
Maple
|
medium
|
Acer rubrum
|
Red Maple
|
medium
|
Aspidistra elatior
|
Cast Iron
Plant
|
medium
|
Aucuba japonica
|
Aucuba
|
medium
|
Berberis thunbergii
|
Japanese
Barberry
|
medium
|
Betula nigra
|
Betula
|
high
|
Buddleja davidii
|
Butterfly-bush
|
high
|
Butia capitata
|
Pindo Palm
|
medium
|
Buxus microphylla
|
Japanese
Boxwood
|
medium
|
Buxus spp. 'Wintergreen'
|
Boxwood
|
high
|
Callicarpa japonica
|
Japanese
Beautyberry
|
high
|
Callistemon spp.
|
Bottlebrush
|
high
|
Calycanthus floridus
|
Sweetshrub,Carolina
Allspice
|
medium
|
Camellia japonica
|
Camellia
|
low
|
Camellia sasanqua
|
Sasanqua
Camellia
|
low
|
Carpinus caroliniana
|
American
Hornbeam
|
medium
|
Cedrus deodora
|
Deodar
Cedar
|
medium
|
Cercis canadensis
|
Redbud
|
medium
|
Chamaecyparis pisifera
|
Falsecypress
|
medium
|
Chamaerops humilis
|
European
Fan Palm
|
medium
|
Chionanthus virginicus
|
Gray-beard
|
medium
|
Clethra alnifolia
|
Clethra
|
medium
|
Cornus florida
|
Dogwood
|
medium
|
Cornus kousa
|
Kousa
Dogwood
|
medium
|
Cortaderia selloana
|
Pampas
Grass
|
low
|
Cryptomeria japonica
|
Japanese
Cedar
|
medium-high
|
Cuphea hyssopifolia
|
False
Heather
|
high
|
x Cupressocyparis leylandii
|
Leyland
Cypress
|
high
|
Cupressus arizonica
|
Arizona
Cypress
|
medium
|
Cycas revoluta
|
Sago Palm
|
medium
|
Daphne odora
|
Winter Daphne
|
low
|
Dietes vegeta
|
African
Iris
|
medium
|
Echinacea pallida
|
Pale
Coneflower
|
medium
|
Eriobotrya japonica
|
Loquat
|
low
|
Euonymus spp.
|
Euonymus
|
high
|
|
Scientific
name
|
Common
name
|
Nutrient
Requirement
|
Eupatorium purpureum atropurpureum
|
Joe Pye
|
low-medium-high
|
Fatsia japonica
|
Fatsia
|
medium
|
Galphimia glauca
|
Thryallis
|
medium
|
Gardenia jasminoides
|
Gardenia
|
medium
|
Gelsemium sempervirens
|
Carolina Jasmine
|
high
|
Ginkgo biloba
|
Ginkgo
|
medium
|
Hedera helix
|
English Ivy
|
medium
|
Hemerocallis spp.
|
Daylily
|
medium
|
Hibiscus rosa-sinensis
|
Hibiscus
|
high
|
Hibiscus syriacus
|
Shrub Althaea
|
high
|
Hydrangea macrophylla
|
Hydrangea
|
low
|
Hydrangea quercifolia
|
Oakleaf Hydrangea
|
medium
|
Ilex cornuta 'Burfordii
Compacta'
|
Dwarf Burford Holly
|
high
|
Ilex crenata
|
Japanese Holly
|
high
|
Ilex glabra
|
Inkberry Holly
|
medium
|
Ilex vomitoria 'Nana'
|
Dwarf Yaupon Holly
|
high
|
Ilex x attenuata
'Fosterii'
|
Foster’s Holly
|
high
|
Ilex x attenuata 'East Palatka'
|
East Palatka Holly
|
medium
|
Ilex x attenuata 'Nellie R. Stevens'
|
Nellie R. Stevens Holly
|
high
|
Ilex x meserveae spp.
|
Blue Hollies
|
medium
|
Illicium parviflorum
|
Anise
|
medium
|
Itea virginica
|
Sweetspire
|
medium
|
Ixora coccinea
|
Ixora
|
medium
|
Juniperus chinensis 'Blue Vase'
|
Blue Vase Juniper
|
medium
|
Juniperus chinensis 'Sargentii'
|
Sargent’s Juniper
|
medium
|
Juniperus chinensis 'Torulosa'
|
Torulosa
|
medium
|
Juniperus conferta 'Blue Pacific'
|
Blue Pacific Juniper
|
medium
|
Juniperus davurica 'Parsonii'
|
Parson’s Juniper
|
medium
|
Juniperus procumbens
|
Japgarden Juniper
|
medium
|
Kalmia latifolia
|
Kalmia
|
low
|
Lagerstroemia indica
|
Crape Myrtle
|
medium
|
Lantana montevidensis
|
Trailing Lantana
|
low
|
Leucophyllum frutescens
|
Texas Sage
|
low
|
Ligustrum japonicum
|
Waxleaf Ligustrum
|
high
|
Liriope muscari
|
Lilyturf
|
medium
|
Liriope
spp. 'Evergreen Giant'
|
Evergreen Giant Liriope
|
low
|
Lonicera spp.
|
Honeysuckle
|
high
|
Loropetalum chinense
|
Fringe Bush
|
medium
|
|
Scientific
name
|
Common
name
|
Nutrient
Requirement
|
Magnolia grandiflora
|
Southern Magnolia
|
medium
|
Mahonia bealei
|
Leatherleaf Mahonia
|
medium
|
Mahonia fortunei
|
Fortune's Mahonia
|
medium
|
Myrica cerifera
|
Waxmyrtle
|
low
|
Nandina domestica
|
Heavenly Bamboo
|
medium
|
Nerium oleander
|
Oleander
|
low
|
Osmanthus fragrans
|
Sweet Olive
|
medium
|
Pennisetum setaceum
|
Red Fountain Grass
|
low
|
Photinia x fraseri
|
Fraser's Photinia
|
medium
|
Pinus spp.
|
Pine
|
low
|
Pittosporum tobira
|
Pittosporum
|
medium
|
Platycladus x 'Green
Giant'
|
Green Giant Arborvitae
|
medium
|
Plumbago auriculata
|
Plumbago
|
low
|
Podocarpus macrophyllus
|
Podocarpus
|
medium
|
Prunus caroliniana
|
Cherrylaurel
|
low
|
Prunus laurocerasus 'Schipkaensis'
|
Cherrylaurel
|
medium
|
Quercus laurifolia
|
Laurel Oak
|
medium
|
Quercus nuttallii
|
Nuttal Oak
|
high
|
Quercus phellos
|
Willow Oak
|
high
|
Quercus virginiana
|
Live Oak
|
medium
|
Rhododendron austrinum
|
Florida Flame Azalea
|
low
|
Rhododendron canescens
|
Pinxter Azalea
|
low
|
Rhododendron spp.
|
Azalea, Rhododendron
|
low
|
Spiraea japonica 'Little Princess'
|
Little Princess Spiraea
|
medium
|
Spiraea spp.
|
Spiraea
|
high
|
Spiraea x bumalda 'Anthony Waterer'
|
Anthony Waterer Spiraea
|
medium
|
Taxodium distichum
|
Bald Cypress
|
low
|
Ternstroemia gymnanthera
|
Cleyera
|
medium
|
Trachelospermum asiaticum
|
Dwarf Jasmine
|
medium
|
Trachycarpus fortunei
|
Windmill Palm
|
medium
|
Tsuga canadensis
|
Canadian Hemlock
|
low-medium
|
Ulmus parvifolia
|
Chinese Elm
|
medium
|
Viburnum awabuki 'Chindo'
|
Chindo Viburnum
|
high
|
Viburnum spp.
'Shasta'
|
Shasta Viburnum
|
medium
|
Viburnum suspensum
|
Sandankwa Viburnum
|
medium
|
Washingtonia robusta
|
Washington Palm
|
medium
|
Zamia floridana
|
Coontie
|
medium
|
|
Table 8. Approximate volume of water
to apply to obtain 50 ml (2.0 oz) of leachate.
|
Container size
|
Water to apply
|
Milliliters
|
Ounces
|
4 to 6 inch
|
75
|
2.5
|
6.5 inch azalea
|
100
|
3.5
|
1 quart
|
75
|
2.5
|
1 gallon
|
150
|
5
|
3 gallons
|
350
|
12
|
5 gallons
|
550
|
18.5
|
Trays (amount/cell)
|
50
|
2
|
|
Containers
should be at container capacity for about 30 minutes (for cavities or cells in
flats and small containers) to two hours (for larger containers) before
applying water. The volumes of water are estimates; so actual amount may vary
depending on crop, substrate, or environmental conditions. Adapted from 1, 2,
3’s of Pour-Thru, North Carolina State University, Whipker et al. 2001.
Fertilizer Storage
Considerations
Granular and
Solution
Local,
state, and federal regulations regarding codes for storage structure compliance
may apply to your situation.
|
Solution fertilizer tanks should
have secondary containment areas for tank contents in case of overflow or
leaks.
|
Foliar Analyses
Foliar
analyses may be used to verify or diagnose deficiencies or toxicities during
the growing season or to determine elemental status of plant tissue in fall or
winter prior to spring flush of growth. A well-designed fertility program can
eliminate the need for tissue testing.
Tissue Sampling
Considerations
Generally,
plants grown under similar conditions can be treated as a group when sampling,
although samples from different species or cultivars should not be mixed. A
tissue sample must be representative of plants sampled. An acre of plants of
the same species that had been treated similarly would require only one to
three composite samples while plants of the same species that have been grown
under different cultural or environmental conditions, should be sampled
separately.
|
Tissue samples should be
representative of plants being sampled.
|
Taking Samples
Sample uppermost mature leaves or shoot tips
on junipers with nonexpanding leaves.
Take samples
just before new flush of growth develops. Each sample should be composed of 20-30
uppermost mature leaves (or shoot tips) selected randomly from the group of
plants. Only one or two leaves for broadleaf evergreens or one or two shoot
tips (1-inch long) for narrow leaf evergreens should be removed from a single
plant to obtain a sample of green tissue that weighs from 10-30 grams
(approximately one ounce). When sampling for diagnostic purposes, collect three
samples of tissue that are the same age from abnormal or problem tissue and
three samples of “normal tissue.” Samples that represent different stages of
the problem should be obtained to determine whether tissue elemental content
changes as the problem progresses. Collect tissue samples in brown paper bags
(not plastic lined) and mark with appropriate identification and sampling date.
|
Tissue samples (10-30 grams) should be collected
from most recently mature growth.
|
Abnormal and normal tissue
samples should be collected for diagnostic purposes.
|
Interpretation of
Tissue Analyses
Elemental
ranges for uppermost mature leaves of woody ornamental plants are given in Table 9. Compare the magnitude of Table 9 values with test results as
well as the ratio between elements. Seldom are all elemental test values within
the ranges given in Table 9, but
these values are intended to be guidelines. Maintain tissue test records for
they are valuable aids when making fertility management decisions and you will
be able to refine the guidelines in Table
9 based on your experience and for your crops and growing conditions. Results
from tissue analyses should serve as guidelines and an aid in making fertility
management decisions that will enhance production and protect air and water
quality.
|
Leaf tissue samples are collected from
recently matured foliage in paper bags labeled with crop name and date.
|
Table 9. Elemental ranges for
uppermost mature leaves of woody ornamentals.
|
Element
|
Percent*
|
Nitrogen
|
2.0 to 2.5
|
Phosphorus
|
0.2 to 0.4
|
Potassium
|
1.5 to 2.0
|
Calcium
|
0.5 to 1.0
|
Magnesium
|
0.3 to 0.8
|
|
Parts
Per Million
|
Iron
|
100 to 200
|
Manganese
|
20 to 100
|
Zinc
|
20 to 75
|
Copper
|
5 to 10
|
Boron
|
20 to 30
|
Molybdenum
|
0.1 to 1.0
|
|
|
|