Publication 8221

FWQP REFERENCE SHEET 9.7

Nutrient Management in
Nursery and Floriculture
Richard Y. Evans, UC Cooperative Extension Environmental Horticulture Specialist,
University of California, Davis; Linda Dodge, Staff Research Associate, UC Davis; and
Julie Newman, UCCE Farm Advisor, Ventura County

UNIVERSITY OF Although many factors have contributed to the nutrient load in surface and ground-
CALIFORNIA water, fertilizer use has been one of the significant influences (Pettygrove et al. 1998).
Division of Agriculture Fertilizer use is an integral part of nursery and floriculture production. It has also
and Natural Resources become a serious environmental issue. The two nutrients that have the greatest poten-
http://anrcatalog.ucdavis.edu tial for harm to water quality are nitrogen (N) and phosphorus (P) in various forms.
Nitrogen and phosphorus loading in surface water bodies contribute to an eutro-
phic environment. Eutrophication is the process whereby a body of water becomes
In partnership with: enriched in nutrients that stimulate the growth of aquatic plants (e.g., algae), which
in turn lead to the depletion of dissolved oxygen in the water. Nitrate pollution of
groundwater has the potential to be the most serious problem because of its impacts
on drinking water quality. Nitrate in drinking water is suspected of playing a role in
the onset of methemoglobinemia and stomach cancer in humans.
The federal Clean Water Act sets standards for the quality of water for a wide range
of purposes, including human consumption, wildlife habitat, recreation, and agricultural
http://www.nrcs.usda.gov and industrial use. Section 303 of the Clean Water Act sets a drinking water standard for
nitrogen. The drinking water standard for nitrogen has been set at 10 parts per million
(ppm) for nitrogen from nitrates (NO3-N), also expressed as 45 ppm nitrate (NO3). In
Farm Water coastal areas (Monterey, San Luis Obispo, Santa Barbara, and Ventura Counties), ground-
water frequently exceeds 10 ppm NO3-N (Pettygrove et al. 1998).
Quality Planning
A Water Quality and It is becoming harder for urban and rural water users in these areas to obtain
Technical Assistance Program drinking water in compliance with this standard. No specific standards have been set
for California Agriculture for phosphorus in freshwater. However, to be in compliance with the federal Clean
http://waterquality.ucanr.org
Water Act, the phosphate concentration should be kept low to avoid eutrophication.
This reference sheet is part of the To prevent eutrophication, phosphates should not exceed 25 parts per billion (ppb) in
Farm Water Quality Planning lakes, 50 ppb in streams flowing into lakes, and 100 ppb in streams that do not flow
(FWQP) series, developed for a
into lakes (US EPA 1986).
short course that provides training
for growers of irrigated crops who
are interested in implementing NITR OG EN IN COAS TAL NU RSER IES AND FL O RICU LT UR E
water quality protection practices.
The short course teaches the
basic concepts of watersheds, Current Nitrogen Use Patterns and Consequences
nonpoint source pollution (NPS), Nitrogen usually is applied to ornamental crops in amounts that exceed the plants’
self-assessment techniques,
and evaluation techniques.
needs. Where fertilizers are injected into the irrigation water, nitrogen fertilizer over-
Management goals and practices use can also result from application of excessive amounts of water and from over-
are presented for a variety of spray that misses the plant containers or beds. Nitrogen application rates vary widely
cropping systems.
among nurseries and greenhouses, but typical annual values range from 1,000 to
7,000 lb/acre (1,100 – 7,800 kg/ha) (Cabrera et al. 1993). Nitrogen uptake by crops
is also variable, but for most ornamental crops nitrogen uptake over the course of a
year is between 400 and 1,000 lb/acre (450 – 1,100 kg/ha), which means the typical
amount applied is more than six times more than is needed for plant growth.
   ANR Publication 8221

There are six possible fates for nitrogen other than uptake by plants:

• Leaching below the root zone. Nitrate moves readily with water that percolates
through the root zone. Most of the nitrogen leached below the root zone of the
crop is in the NO3 form. Over the long term, much of the applied nitrogen leaches
out of the root zone and becomes a potential contaminant of groundwater.

• Soilborne erosion losses. Nitrogen in soil aggregates and container media can be
moved by water or wind. Both ammonium (NH4) and nitrate (NO3) will move with
sediments.

• Denitrification. Soil microbes can convert NO3 to nitrogen gas that is then lost
to the atmosphere. This denitrification occurs to some extent in all soils when
oxygen levels are low, for example after irrigation or rainfall has saturated soils. In
heavy clay soils with poor drainage or in soils with restrictive layers that prevent
drainage, nitrogen losses through denitrification may be 15 to 50 percent of applied
fertilizer nitrogen. In general, only a small percentage of applied nitrogen is lost
through denitrification.

• Immobilization in and mineralization from organic matter. Applied nitrogen may be

tied up (immobilized) in soil organic matter or in the biomass of soil microbes as
they work to decompose crop residues. Large amounts of applied nitrogen can be
temporarily immobilized into organic nitrogen by the soil microbes, for example,
when low-N plant material is incorporated into the soil. Organic nitrogen is slowly
and constantly being recycled back into plant-available nitrogen through a process
called mineralization. The loss of soil organic matter reduces the capacity of the soil
to retain applied nitrogen.

• Residual soil nitrogen. Nitrogen may remain in the soil as residual soil nitrogen,
available for subsequent season uptake. This residual soil nitrogen generally builds
up over a season, as long as in-season irrigation is controlled to minimize leaching
losses. During a typical winter in most of coastal California, however, rainfall is
sufficient to leach most of the residual NO3 out of the root zone.

• Ammonium volatilization. When animal manure, urea, or ammonium-containing

fertilizers are left on the surface of the soil, nitrogen can be lost to the air as
gaseous ammonia. This loss can be significant in alkaline (high-pH), sandy soils. If
manure or fertilizers are incorporated within a few hours after application, this loss
is negligible.

Nitrogen Application
Nitrate (NO3) is the predominant form of fertilizer nitrogen used by nurseries and
greenhouses. Nitrogen may also be applied as urea or ammonia (NH4). Urea is rapidly
converted to NH4 in the soil. Although NH4 is readily taken up by plants, it accounts
for only a small percentage of any crop’s nitrogen uptake. The microbial process called
nitrification rapidly converts NH4 to NO3 in warm, moist soils. The majority of the
nitrogen that is taken up by plants will typically be in the form of NO3. Also, since
NH4 is bound to soil particles by its positive charge, it is less easily leached than NO3.
For these reasons, NO3 is the focus of nitrogen management strategies.
Liquid feeding (fertigation) is widely used by both nurseries and greenhouses. After
the initial cost of injectors, it is less expensive than using controlled-release fertilizers and
it is well suited to production of large areas of uniform crops because the fertilizer concen-
trations can be varied according to crop needs (for example, the nitrogen supply for a
   ANR Publication 8221

chrysanthemum crop can be decreased late in the crop’s season). The major disadvantages
of liquid feeding are its inefficiency in putting nitrogen into the root zone and its suscepti-
bility to leaching losses of nitrogen as a result of excessive irrigation.
Controlled-release fertilizers can greatly reduce nitrogen losses if they are cor-
rectly applied. Nutrient release rates are controlled by the properties of the capsule
walls and by temperature and moisture, not by the plants’ needs. This type of formula-
tion restricts nitrogen leaching losses from over-irrigation to the small amount that has
been released since the previous irrigation. Unlike fertigation, however, application
of nutrients cannot easily be varied according to crop needs. For example, an amount
of controlled-release fertilizer that releases enough nitrogen to feed a rapidly growing
plant (for example, a 40-day-old chrysanthemum that requires as much as 30 mg N
per day) would be far more than the amount needed for a young plant or one that is
no longer taking up much nitrogen (for example, a 70-day-old chrysanthemum). The
excess nitrogen that is released can be lost to leaching if the plants are over-irrigated.
The likelihood of nitrogen leaching losses from controlled-release fertilizers is
greatest during the first few weeks after planting, when plant root systems are limited,
nutrient demand is low, and plants are consuming relatively small amounts of water.
It is best to apply controlled-release fertilizers just below the plant roots at the time of
planting (sometimes called dibbling) or to broadcast the fertilizer onto the soil surface.

Crop Growth Stage and Nitrogen Requirements

Nutrient management practices should be targeted toward maintaining adequate min-
eral nitrogen in the root zone and minimizing the leaching of nitrates below that zone.
Actual nitrogen fertilizer requirements are known for only a few nursery and floricul-
ture crops. Plant requirements for nitrogen vary according to growth rate and stage of
development. For example, the rate of nitrogen uptake for potted chrysanthemums
increases during vegetative growth and then decreases sharply after flower buds form.
Poinsettias behave in a similar fashion. Roses and some other woody species exhibit
a cyclical pattern of nitrogen uptake that is related to episodes of shoot growth and
either pruning or dormancy. Depending on the nitrogen application method, it may be
possible for growers to adapt the fertilizer program to match changes in plant nitrogen
demand.
Leaf tissue analysis for nitrogen provides a convenient way to determine the short-
term need of some ornamental crops for additional nitrogen applications (see table 1). The
mineral composition of a leaf blade depends on many factors, such as its stage of develop-
ment, climatic conditions, availability of mineral elements in the soil, root distribution and
activity, irrigation, water status, and so on. The plant responds to all of these factors, and
the composition of the blade reflects this response. Nutrient concentrations required for
optimal growth and nutrient levels above which toxicity occur have been established for
many fruit and nut crops, but values are available for only a few ornamental crops. Check
with your local University of California Cooperative Extension Farm Advisor for more
detailed nitrogen fertilizer requirements and application schedules for your area. By testing
at the correct time, you can ensure that adequate plant NO3--N concentrations are available
in the soil and that unnecessary fertilizer applications are eliminated.
   ANR Publication 8221

Table 1. Nitrogen content (grams) for certain ornamental crops at commercial maturity

Crop (and container size or unit) Tissue nitrogen

g
Acorus ‘Ogon’ (1-gallon) 0.6 – 0.9
Azalea (6-inch) 0.5 – 0.7
Chrysanthemum (6-inch) 1.2 – 1.7
Cosmos (6-inch) 0.5 – 1.0
Euonymus japonica (1-gallon) 0.9 – 1.6
Geranium (6-inch) 0.6 – 1.0
Holly (6-inch) 0.5 – 0.7
Hydrangea (1-gallon) 1.75
lmpatiens (4-inch) 0.3 – 0.4
Pistachia chinensis (5-gallon, 1 season) 2.6
Platanus acerifolia (5-gallon, 1 season) 4.7
Poinsettia (6-inch) 0.5 – 0.7
Quercus agrifolia (5-gallon, 1 season) 0.6
Rose (per harvested stem) 0.2

Phos p ho rus IN COAstal nurser i es and fl o ricu ltu re

Phosphorus (P) is present in the soil in a number of chemical forms: a very small
amount of soluble, inorganic phosphorus in the soil water, phosphorus adsorbed onto
soil particles, chemical precipitates, and phosphorus as a constituent of organic mat-
ter. These different phosphorus sources establish equilibrium in the soil; as plants
remove soluble phosphorus, other forms replenish the soluble phosphorus supply. In
mineral soils, phosphorus solubility is low and most phosphorus is held in chemical
precipitates that are relatively immobile. These forms of phosphorus are not usually
transported off site unless rainfall or irrigation causes the movement of sediments
that contain phosphorus. In contrast, the solubility of phosphorus in soilless media is
relatively high, especially in acidic container media. This soluble phosphorus can be
leached out of containers by rainfall or excessive irrigation. Leaching losses of 30 to
60 percent of fertilizer phosphorus are common. These leaching losses can be reduced
significantly if you incorporate ferrous sulfate into the medium at a rate of 4.8 lb per
cu yd (2.8 kg/m3) (West 1990). In addition, phosphorus that is bound to particles of
soilless media that have been spilled or washed out of containers can move off site in
irrigation water or rainwater. The movement of phosphorus into streams and lakes can
lead to algal blooms and subsequent fish kills.
Common laboratory soil test procedures provide an estimate of the amount of
phosphorus in the soil that is available to plants. Unlike soil nitrate testing, which
measures the actual amount of nitrate present, soil testing for phosphorus as carried
out by most laboratories gives an index value or ranking of the available phospho-
rus supply. Researchers over many years have calibrated these soil test procedures in
greenhouse and field trials so that the results can be used to predict whether a crop
is likely to respond to additional phosphorus fertilization. In most ornamental crops,
plant demand for phosphorus does not exceed about 15 mg per plant per day. For
field-grown woody nursery plants, the typical recommendation is to supplement exist-
ing soil phosphorus with fertilizer to provide a total of 44 pounds per acre (49 kg/ha)
of actual phosphorus per year (100 pounds per acre [112 kg/ha] when expressed as
P2O5) (Davidson, Mecklenburg, and Peterson 1994). For container-grown crops, phos-
phorus is usually added to the growing medium as superphosphate (2 lb per cu yd
   ANR Publication 8221

[1.2 kg/m3]) or triple superphosphate (1 lb per cu yd [0.6 kg/m3]) prior to planting.

Alternatively, phosphorus can be added as a component of a complete, controlled-
release fertilizer.
It is not normally necessary to supplement the pre-plant addition with a liquid
feed source of phosphorus unless the crop will be grown for more than 3 to 6 months.
In that case, injection of phosphorus into the irrigation water at a rate of 15 ppm is
effective. However, liquid feeding with phosphorus is subject to the same problems
that are associated with nitrogen.
The best way to keep phosphorus from moving off your property is to reduce
runoff. Evaluate your property so that you know the surface drainage patterns and
then take action to prevent excessive runoff from reaching surface water bodies. Filter
strips, grassed waterways, sediment basins, nutrient management, and other NRCS
practices should be used in conjunction with soil testing for effective prevention of
phosphorus runoff.

I nfl ue nce o f Irr igat ion

Uniform delivery of irrigation water is critical in achieving good nutrient management.
Growers who irrigate efficiently will have less runoff and fewer leaching losses to con-
tend with, and therefore fewer nutrient management problems. The key steps toward
achieving high irrigation efficiency (where a high percentage of the applied water
remains in the root zone, available for plant uptake) are to apply water evenly across
the field or greenhouse and to schedule irrigations so they will deliver the proper
amounts of water at the proper time.
The evenness with which water is applied across the field or greenhouse is mea-
sured as the distribution uniformity (DU). The greater the DU, the greater the potential
for maximum irrigation efficiency. Irrigation system performance is dependent upon
system design and maintenance, proper or improper redesigns or retrofits, equipment
age, and water pressure variability, as well as on various management practices. For
example, grouping plants according to their expected water use and capturing runoff
water for recycling or filtering can significantly improve a field’s irrigation efficiency.
The distribution uniformity of a sprinkler irrigation system can also be affected signifi-
cantly by wind conditions.
Conventional sprinkler or furrow irrigation techniques often have poor distribu-
tion uniformity or irrigation efficiency. Microirrigation (drip tape, drip emitters, micro-
sprayers/sprinklers) has the potential for higher distribution uniformity than other
irrigation methods, but frequently these systems are not designed and maintained well
enough to meet this potential. These conditions were noted in irrigation system evalu-
ations in San Luis Obispo and Santa Barbara Counties (Pitts et al. 1996). Low distri-
bution uniformity and low efficiencies often lead to over-irrigation, with excessive
amounts of water lost to deep percolation (drainage) below the crop’s root zone.
Growers need to know how much water their crops use and then irrigate accordingly.
Water use can be measured directly in nurseries and greenhouses that produce plants in
containers. Using a scale that expresses weights to the nearest gram, growers can record
the weights of a representative number of pots 1 hour after irrigation and again the next
day, just before irrigation. The difference in weight, expressed in grams, represents water
use in milliliters (ml). By periodically taking measurements, the grower can anticipate a
crop’s average seasonal water needs. The average daily water use of some mature ornamen-
tal crops grown in Davis, California, is presented in table 2.
   ANR Publication 8221

Table 2. Average daily water use of some ornamental crops grown in Davis, California

Crop (and container size or unit) Water use

ml / day oz / day

Acorus ‘Ogon’ (1-gallon, outdoor shade) 140 5.0

Aucuba japonica (1-gallon, outdoor shade) 100 3.5

Camellia ‘Winter’s Star’ (1-gallon, outdoor shade) 100 3.5

Chrysanthemum (6-inch) 240 8.0

Dietes vegeta (1-gallon, outdoor) 130 4.5

Holly (1-gallon, outdoor shade) 140 5.0

Hydrangea (1-gallon, outdoor shade) 340 11.5

Hydrangea (6-inch, greenhouse) 175 6.0

Impatiens (4-inch, greenhouse) 100 3.5

Juniperus scopulorum ‘Moonglow’ (1-gallon, outdoor) 140 5.0

Lantana ‘Pink Caprice’ (1-gallon, outdoor) 200 7.0

Lavandula dentata (1-gallon, outdoor) 160 5.5

Magnolia grandiflora (5-gallon, outdoor) 340 11.5

Nandina domestica (1-gallon, outdoor shade) 120 4.0

Pelargonium (6-inch, greenhouse) 175 6.0

Penstemon ‘Red Rocks’ (6-inch, greenhouse) 150 5.0

Pistacia chinensis (5-gallon, outdoor) 580 20.0

Platanus racemosa (5-gallon, outdoor) 940 32.0

Prunus ilicifolia (5-gallon, outdoor) 250 8.5

Quercus agrifolia (5-gallon, outdoor) 260 9.0

Quercus lobata (5-gallon, outdoor) 335 11.0

Rhododendron (1-gallon, outdoor shade) 200 7.0

Rose (mature greenhouse plant for cut flowers) 400 14.0

Sequoia sempervirens (5-gallon, outdoor) 390 13.0

Weigela ‘Variegata Nana’ (1-gallon, outdoor shade) 160 5.5

A grower can estimate a crop’s water needs by referring to local values for refer-
ence evapotranspiration (ET). Evapotranspiration is the water lost by plant uptake
from the soil and by evaporation from the soil surface. Table 3 presents the estimated
water use of greenhouse and outdoor crops grown near the coast in San Mateo County,
based on evapotranspiration. The available measured values for a few summer flower
crops are about 20 percent lower than these calculated values show, so this method for
estimating water needs is good but not perfect. Growers interested in estimating their
own crops’ water requirements should contact their local UC Cooperative Extension
County Office.
   ANR Publication 8221

Table 3. Calculated average daily water use of ornamental crops in Half Moon Bay, based on historic
evapotranspiration values

Month Outdoor crop Greenhouse crop

oz / ft2 mL/m2 oz / ft2 mL/m2

Jan 4.0 1.3 6.0 1.9

Feb 4.3 1.4 6.4 2.0

Mar 6.4 2.0 6.4 2.0

Apr 7.7 2.5 5.8 1.8

May 10.4 3.3 7.8 2.5

Jun 11.2 3.6 8.4 2.7

Jul 11.4 3.6 8.6 2.7

Aug 10.9 3.5 8.2 2.6

Sep 9.3 3.0 7.0 2.2

Oct 7.4 2.4 7.4 2.4

Nov 3.4 1.1 6.1 1.9

Dec 2.7 0.9 5.3 1.7

Excessive irrigations can have a significant impact on soil NO3-N levels. In a field
with 20 ppm NO3-N in the soil solution, 1 inch (2.5 cm) of water leaching from irri-
gation may carry with it as much as 20 lb N per acre (22 kg/ha) out of the root zone.
In addition, irrigation water can be a source of NO3. Many agricultural wells now con-
tain more than 10 ppm NO3-N. Application of 1 foot (30 cm) of irrigation water that
contains 10 ppm NO3-N would be equivalent to applying nitrogen at a rate of 27 lb
per acre (30 kg/ha).
Efficient nitrogen fertilizer management is a necessity to keeping further NO3
pollution of groundwater to a minimum and requires that a grower take into account a
variety of site-specific factors. A variety of techniques is available to help growers keep
track of how much fertilizer is in the soil and whether or not it is sufficient to meet
current crop needs. Using the information gathered from these techniques, a grower
can make decisions about when to fertilize and when to water that will minimize
harmful and expensive losses of nutrients and moisture from the root zone.
   ANR Publication 8221

Refere nce s
Cabrera, R. I., R. Y. Evans, and J. L. Paul. 1993. Leaching losses of N from con-
tainer-grown roses. Scientia Horticulturae 53:333–345.
Davidson, H., R. Mecklenburg, and C. Peterson. 1994. Nursery management:
Administration and culture. Englewood Cliffs, NJ: Prentice Hall.
Pettygrove, G. S., S. R. Grattan, B. R. Hanson, T. K. Hartz, L. E. Jackson, T.
R. Lockhart, K. F. Schulbach, and R. Smith, eds. 1998. Production guide:
Nitrogen and water management for coastal cool-season vegetables. Oakland:
University of California, Division of Agriculture and Natural Resources.
Publication 21581.
Pitts, D., K. Peterson, G. Gilbert, and R. Fastenau. 1996. Field assessment of irrigation
system performance. Applied Engineering in Agriculture 12(3): 307–313.
US EPA. 1986. Water quality criteria for water 1986. Rep. 440/5-86-001.
Washington, DC: US EPA Office of Water.
West, K. H. C. 1990. The role of media in phosphorus nutrition and growth of
Chrysanthemum × morifolium. M. S. thesis. University of California, Davis.

Acknow le dgm ent

Adapted from UC ANR Publication 8098, Nutrient management in cool-season vegeta-
bles (Reference sheet 9.9, Farm Water Quality Planning series).

Fo r M o re I nf o rmat ion:
You will find related information in these titles and in other publications, slide sets,
CD-ROMs, and videos from UC ANR:
The Farm Water Quality Plan, Publication 9002
Nutrient Management Goals and Management Practices for Nursery and Floriculture,
Publication 8122
Sediment Management Goals and Management Practices for Nursery and Floriculture,
Publication 8124
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Publication 8221
   ANR Publication 8221

This publication has been anonymously peer reviewed for technical accuracy by University of
California scientists and other qualified professionals. This review process was managed by the
ANR Associate Editor for Agronomy and Range Sciences.

©2007 by the Regents of the University of California Division of Agriculture and Natural Resources.

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