Assessing and Supplying Fertilizer
Needs Under Organic Systems
M. Elena Garcia, Professor
Horticulture Dept.
University of Arkansas
Conventional vs. Organic Plant
Nutrition
Fundamental principles the same, whatever the
production system used:
Conventional systems:
Relies on targeted short-term solutions
Reactive
Application of soluble fertilizers
Plant Nutrition in Organic
Systems
Organic systems: Long-term solutions
and ecological approach
Preventive not reactive
Work within natural systems and cycles
Maintain or increase long-term soil fertility
Use renewable resources as much as
possible
Management of soil organic matter (OM)
Rotation design for nutrient cycling
Organic Fertilizers
Naturally occurring materials of
biological or mineral origin and are low
in nutrient concentration or solubility or
have both properties
May be altered physically in processing
for agricultural use, but chemical
processing does not usually occur
(Baker, 2010)
Advantages and Disadvantages
of Organic Fertilizers
Advantages
Mild, non-caustic
materials
Slow release makes them
available for longer time
If high OM content =
improvements in soil
physical properties
Sources of many
essential elements
Recycling of materials
Disadvantages
Low concentration of
nutrients = large
application
Slow release may not
supply plant’s immediate
needs
Concentration may be too
low to supply plant’s
needs
Expense
Conventional vs. Organic Plant
Fertilizers
Difference between organic and
synthetic fertilizers:
Not in the kind of nutrients supplied but,
Rate of release
Generally: Organic fertilizers release
nutrients slowly and in response to
environmental factors such as soil
moisture and temperature
Organic Regulations
Organic regulations require growers to
rely on the use of manures, cover crops,
crop rotations, and the use of untreated
products
Organic Horticulture Systems
Intensive
High dependency on imported nutrients
Crops have high demand for major and
minor nutrients
Usually several crops within one growing
season
Crop rotation difficult in perennial systems
Soli fertility maintenance major concern
The Fertility Equation: Soil
The ability of the soil to supply nutrients
needed for plant growth.
Recognize:
physical,
biological, and
chemical
components
these are
interrelated.
Soil Quality
Capacity of a soil to function within
ecosystem boundaries to:
• Sustain biological activity
• Maintain environmental quality
• Promote “plant health”
• It is not a soil property
• Soil health = soil quality
Soil Health
Physical
Chemical
Biological
Overlapping of the
physical, chemical,
and biological
properties
•General picture of
soil’s capacity to
support plant growth
without degradation…
sustainability
Ability of Soils to Supply Nutrients
Soil texture
Soil chemistry
Soil moisture
Soil tilth
Soil aeration
Soil Organic Matter (SOM)
Organic matter will prevent deterioration
of the physical properties of the soil by
serving as an energy source (i.e. food)
for microorganisms which promote
stable aggregation of the soil particles.
Essential nutrients are obtained by
plants as organic matter decomposes
Using Organic Amendments to
Improve Fertility





Organic amendments
increase OM content in
soil
OM increases CEC,
increasing nutrient
storage capabilities
OM supplies plant
nutrients
OM improves buffering
capacity (stabilizes pH)
OM promotes/aides
beneficial microbial
populations

Types of Organic
Amendments:
–
–
–
–
–
Animal Manure
Cover Crops
Crop residues
Yard debris
Biosolids
Plant Available N
Knowing total amounts of N-P-K does not
tell how much is available
Manure: total N is ~ 25-40%
Available N in compost is < 10% (stabilized
from)
Plant Available Nitrogen (PAN) from Amendments ( Gale et al)
PAN (%)
C:N
NH4-N (g kg-1
Field
Lab
Dry broiler litter
9
6.3
41
45
Composted dry broiler
litter
9
7.3
38
45
Composted chicken
litter
8
5.6
47
25
Yard-trimmings
13
3.0
19
25
Composted yard
trimmings
17
0.7
3
5
Bio-Gro pelleted fish
byproduct
5
1.1
77
57
Feather meal
4
2.0
99
74
On-farm compost
15
0.1
6
4
Composted rabbit
manure
27
0.1
-6
-7
Amendment
SOM, pH and Buffering Capacity
SOM has ability to moderate major
changes in pH
Soil pH is determined by amount of
positively charged H ions (H+) in the soil
solution
OM buffers the soil
Making H+ more constant
Taking and releasing H+
Pre-Plant Preparations
Soil analysis must!!
Adjust pH prior to planting.
Difficult to change pH after establishment.
Addition soil amendments prior to
planting.
Generally, fruits crops do not respond P
applications after establishment.
Cover Crops
•
•
•
•
Grasses or legumes
grown in pure or mixed
stands
Planted after harvest of
primary crop, as a fallow
crop, or interplanted with
primary crop
Can be incorporated into
soil or left on surface as
residue
Sometimes referred to as
green manure, catch
crop, or living mulch
depending on purpose
•
Benefits:
– Reduced soil erosion
– Improve soil structure
– Suppress of weeds,
insects, and diseases
– Enhance soil fertility
• Increases OM
content
• Retention of nutrients
• Prevention of
leaching losses
• Increases N content
• Greater diversity of
soil microbes
Crop Residue
•
•
•
•
Portion of plant
remaining after harvest
left on soil surface
Widely used method of
maintaining OM
May be partially
incorporating at
planting time
Can harbor disease
and insect pests
– May be avoided by: crop
rotation, removing
residue to compost it, or
proper timing of
incorporation
•
Benefits:
– Increases OM content
– Increases soil
aggregation
– Prevents soil crusting
and erosion
– Improves water
infiltration rates
– Provides nutrients
Mulches
Helps keep soil cool in summer
Helps retain soil moisture
Adds organic matter, helps in nutrition
Improves soil structure
Helps reduce weed pressure
Increases soil water holding capacity
Tillage Effects on Fertility
•
Purpose:
– Prepare seedbed
– Control weeds
– Break up traffic pans &
soil compaction
– Incorporate crop
residue
•
Tillage and cultivation
practices should be
implemented that
maintain or improve soil
health and minimize
soil erosion.
•
Negative effects of
conventional tillage on
fertility:
– Destroys soil organic
matter
– Decreases diversity
and populations of soil
microbes and
earthworms
– Decreases water
infiltration rates
– Increases compaction
Effect of pH and Element
Availability in Mineral Soils
organicgarden.org.uk/?page_id=2387
Nutrient Budgets
Commonly used to evaluate the effects
of nutrient management on farm and
field sustainability
Are the outcome of a simple accounting
process that tracks inputs and outputs
to a given, defined system over a fixed
period of time
Useful when accounting for renewable
resources in production and processing
as a way to avoid pollution and waste.
The Nutrition Equation
Balancing Act
Plant needs
Soil
The Fertility Equation: Plant Demand
Plant health
Ability of root system to absorb nutrients
Soil type
pH
Soil water content
Ability of plant to utilize
nutrients
Physiological stage
Crop load
Weed control
Essential Elements
16 elements are classified as essential
for all crops
Two criteria are used to establish the
essentiality
If the plant fails to grow and complete its
life cycle without this element
Constituent of a necessary metabolite b
Law of the Minimum
Justus von Liebig, generally credited as the "father of
the fertilizer industry", formulated the law of the
minimum: if one crop nutrient is missing or deficient,
plant growth will be poor, even if the other elements
are abundant.
Essential Elements
From air
Carbon: CO2
Hydrogen: H2O
Oxygen: H2O and O2
Plant Needs for Growth and
Development
Macronutrients
Nitrogen: NH4+,NO3Phosphorus: H2PO4-, HPO42Potassium: K+
Calcium: Ca++
Magnesium: Mg++
Sulfur: SO42-
Plant Needs
Micronutrients:
Iron, Zinc,
Manganese, Copper,
Boron, Molybdenum,
Chlorine, Silicon,
Sodium, Cobalt,
Vanadium essential to
some plants
Role of Mineral Nutrients
Mineral nutrients affect crop quality and
yield
Direct
Indirect
N excess over stimulates growth:
Fruit often softer, does not store as well
Shading causes loss of color in fruit
Flow of Nutrients into Plant
Mature leaf
Roots
xylem
Phloem
Fruit
Simplistic view
• Xylem transports
water and mineral
nutrients from roots to
the rest of the tree
• Phloem transports
leaf-assimilated
compounds through
the stems to roots
Nutrient Movement from Soil to Plant
Mobile vs. immobile elements
N
P
K
S
Ca
Mg
B
Zn
Cu
Mn
Mo
Ionic
Form
NH4+
NO3H2PHO4K+
SO4Ca+
Mg++
H3BO3
Zn++
Cu++
Mn++
MoO4-
Soil Mobility Plant Mobility
Immobile
Mobile
-Immobile
-Immobile
Mobile
Immobile
Immobile
Mobile
--Immobile
--Immobile
--Immobile
Immobile
Immobile
Mobile
Immobile
Mobile
Mobile
-- Immobile
Mobile
--Immobile
Immobile
Immobile
Immobile
Immobile
Monitoring Mineral Nutrition
Knowledge of:
• Site/soil characteristics and chemistry
• Plot design requirements
• Plant physiological stages
• Fertilizer inputs
• Cultural practices
• Tissue analysis
• Observation and judgment
Nutrient Status Limitations
Crop
Rootstock
Variety
Soil depth
Root distribution
Soil water status
Temperature
Crop load
Soil pests
Soil Chemistry / nutrient availability
Nitrogen Utilization
Tagliavini, et al. 2000
Phosphorous Utilization
Tagliavini, et al. 2000
Interactions
N: Too much = Poor fruit quality
Too much N may create nutrition imbalances
N deficiencies common in organic orchards during
establishment years
K: Pre-planting applications
Depletion common
Adding K without Mg can create Mg deficiencies
P: Pre-plant application very important
Too much P can create Zn and Cu deficiencies
Diagnosing Nutritional Status
Soil analyses: Tell what is in the soil– pH, OM
Limitations:
Sampling
Time
Depth
Foliar analyses: Tell what is actually in the plant
Limitations:
Sampling
Time
Condition of sample
Soil vs. Foliar Analyses
Many studies show poor correlation
between soil tests and leaf analyses in
orchards
Deep rooted
Accumulation of nutrients through out the
year
IMPORTANT TO DO BOTH ON A
REGULAR BASIS!
Ground vs. Foliar Application
The most efficient way to apply nitrogen,
phosphorus, potassium, and magnesium is
by ground application.
Foliar applications of these elements should
be viewed as temporary or emergency
solutions only.
Boron, zinc, copper, and manganese can be
added by either foliar or ground application.
The foliar method is usually preferred
because very small amounts are applied per
acre.
Sources for Organic Fertilizers
Sources of Organic Fertilizers, and
amendments
http://attra.ncat.org/attra-pub/orgfert.php
How to convert an inorganic fertilizer
recommendation into an organic one
http://pubs.caes.uga.edu/caespubs/pubs/PDF/C
853.pdf
crops_generic.pdf
http://www.omri.org/
Acknowledgements
This presentation address general organic production practices. It is to be
to use in planning and conducting organic horticulture trainings. The
presentation is part of project funded by a Southern SARE PDP titled
“Building Organic Agriculture Extension Training Capacity in the
Southeast”
Project Collaborators
•
Elena Garcia, University of Arkansas CES
Heather Friedrich, University of Arkansas
Obadiah Njue, University of Arkansas at Pine Bluff
Jeanine Davis, North Carolina State University
Geoff Zehnder, Clemson University
Charles Mitchell, Auburn University
Rufina Ward, Alabama A&M University
Ken Ward, Alabama A&M University
Karen Wynne, Alabama Sustainable Agriculture Network