Soils and their Sustainable
Management
UME-Baltimore City
extension.umd.edu/anmp
December 2015
Plan for today ….
•soil composition
•soil testing
•nutrient sources
•soil sustainability (soil health)
•nutrient management planning
What is Soil?
• the living skin of the Earth (Ian Pepper, soil
microbiologist)
• crucible of terrestrial life (Daniel Hillel, soil physicist)
• the pedosphere
• the interface between the lithosphere, hydrosphere
and atmosphere (ecologists)
• a medium for plant growth (edaphologists)
• phenomena of nature (natural bodies) (pedologists)
mysciencebox.org
What are Soils?
• reactive, dynamic, three-phase ecosystems composed of
solids, liquids and gases
topsoil
several
days after
rainfall or
irrigation
25%
25%
48%
2%
Minerals
Air
Water
Organic Matter
fine medium
texture texture
available water medium high
capacity
nutrient holding high medium
capacity (CEC)
infiltration &
slow medium
percolation
crusting
high medium
compaction
high
medium
coarse
texture
low
low
fast
low
low
Harsh Reality!
•textural groupings set the stage for
many physical properties
−parent material
−time
•management can ameliorate extremes
to a certain extent
Do you know the texture of the
growing areas you manage?
•What is it?
•How did you determine the texture?
−soil testing lab reported it (extra $$)
−texture by feel
−soil map with published information
The Other Soil Solid Material: Organic Matter
Humus
75%
10%
Biomass
15%
Residues &
By-Products
Source: USDA
Biomass: What It Does
•participates in nutrient cycling
−comminute (shred or fragment) plant and
animal residues, using what they can utilize
and leaving behind what they cannot (mesoand macroorganisms)
•mineralization (microorganisms)
−conversion of organic form of an element to
an inorganic form
−protein to amino acid to ammonium
Biomass: What It Does (cont.)
•creation of biopores
−larger organisms (meso and macro) move
through soil creating channels or pores
• channels promote water infiltration and create
a healthy balance between large and medium
pores
−disseminate spores, microbes, nutrients
and waste products
Resources about Soil Organisms *
TED Talk – How Bacteria “Talk”
http://www.ted.com/talks/bonnie_bassler_on
_how_bacteria_communicate.html
Soil Biology Primer
http://soils.usda.gov/sqi/concepts/soil_
biology/biology.html
Residues and By-products:
What They Are
•dead stuff
− crop residues, dead roots and bodies of soil
creatures
•by-products
− materials that plant roots and soil creatures
release or exude into the soil
Residues and By-products:
What They Do
•fuel and nutrients for soil organisms
−energy and nutrient source for most of the
soil creatures
•formation and maintenance of soil
aggregates (structure or architecture)
−sticky and gummy by-products of residue
decomposition hold soil particles together
in clumps or aggregates
More on By-products (Exudates) *
•microbial exudates kill off competing
organisms
−domestication of soil microbes - antibiotics
•root and microbial exudates solubilize
minerals to release nutrient contained
therein
•root exudates feed a huge population
of microbes in the rhizosphere
Humus
•relatively stable end product of residue
decomposition
•composes the majority of organic matter
•resists further decomposition (1% per year)
•it is not a good nutrient or energy source for
soil creatures
Humus: What It Does
•very small in particle size & high surface
area
•charged sites at many locations on the
surface
•effective at holding water and nutrients
Mantra
Soil is a living factory
of macroscopic and
microscopic workers
who need food to eat
and places to do their
work.
USDA-NRCS
So, what about the pore space…
Different Pores Perform Different
Functions
• macropores (large pores)
− drain quickly after rain or irrigation
− allow rapid infiltration of rainfall and
replenishment of oxygen in the root zone
• mesopores (medium-sized pores)
− “storage pores”
− hold water in a form most plants can use
• micropores (very small pores)
− water is held too tightly to be use to most plants
− microbes live in water films
Soil Aeration – the interplay between water
and air
micro meso macro
biomass
organic
solids
residues &
by-products
soil
solution
soil
air
sand
silt
clay layer
minerals
humus
Pore space
inorganic
solids
oxides
clay
SSSAJ v. 75
What is a fertile soil?
•one that provides an adequate supply of
all nutrients throughout the entire
growing season
•test soil to determine if soil is too acidic
and major nutrients are in inadequate
supply
−lime first, them add other nutrients when
needed
What is Soil?
Soil is a mixture of mineral (inorganic)
and organic materials found at the Earth’s
surface that reflects its parent material,
landscape position, climate, vegetation
and the time that it has been forming
Growing Media
commercial growing media
−mixes of various organic and, in most cases,
inorganic materials that provide mechanical
support as well as water retention
• peat, coir, compost, bark, perlite, vermiculite
compost
−a material that has undergone a
thermophilic, aerobic process which changed
readily decomposable compounds to more
stable compounds
Soil or Growing Medium?
Soil
• 2-5%
organic
matter
Heavily
Amended Soil
• 10-20%
organic matter
soil test
Growing
Medium
• 50-95%
organic
matter
saturated
media extract
(SME)
1
soil (2.5 g)
+
extractant (25 ml)
2
shake (5 min, 200 os/min)
3
filter
analyze
growing media
+
distilled water or DTPA solution
to saturation
mix
allow to equilibrate (1 hr)
remove solution
analyze
What is a Management Unit in a Natural
Setting?
 an area with a similar complex of soils
 an area which has been and will be managed
similarly
− same crops
− same fertility regime
How Many Management Units aka Growing
Areas or Beds?
•Situation:
stripped sod
flat area
mapped Glenelg silt
loam
rototilled after
amending
cropped to tomatoes
gypsum
(5T/A)
+
poultry
litter
(3T/A)
lime
(2T/A)
+
poultry
litter
(3T/A)
gypsum
(5T/A)
+
dairy
manure(
15T/A)
soil acidity:
the adverse
condition in the
soil solution in
humid regions
Soil Sampling Card
Essential Soil Test Information
pH
texture
magnesium (Mg)
phosphorus (P)
potassium (K)
calcium (Ca)
organic matter (OM)*
(*This test is highly advisable but is not strictly
essential to get a recommendation.)
Where Can Soils Be Tested?
Regulations require that planners use UME
recommendations.
Certain labs’ procedures have been
correlated with UME’s procedures.
After a conversion process, UME
recommendations can be generated.
Compatible Labs for Commercial Growers
Labs whose soil test data can be converted to the UME
equivalent include:
−A & L Eastern Analytic
−Agri-Analysis
−Brookside
−Penn State




Spectrum Analytic
University of Delaware
Waters
Agro Lab
See “Comparison of Soil Test Labs” in this chapter.
Soil test lab comparison
Soil Testing is not Standardized
Soil test
results
Soil Tests and Their Interpretation
Soil Test Category Interpretation
very low, low
nutrient will likely limit plant
growth
medium
nutrient may not be limiting;
addition of nutrient advisable
sufficient, optimum or
high
nutrient supply is OK; no
more is needed
high, very high or
excessive
nutrient supply is more than
adequate; no more is needed
Blood
meal
13-0-0
46-0-0
0-0-22
0-45-0
Nutrient Sources
•fertilizers
−confusing terminology
−“organic” and organic (carbon-backbone)
−commercial (labeled and purchased)
−soluble vs. slow-release
Tyson and Cabrera, 1993, CSSPA
The Nitrogen Cycle
Component
Input to soil
Loss from soil
Atmospheric
nitrogen
Atmospheric
fixation
and deposition
Industrial fixation
(commercial fertilizers)
Crop
harvest
Animal
manures
and biosolids
Volatilization
Plant
residues
Runoff and
erosion
Biological
fixation by
legume plants
Plant
uptake
Imm
Organic
nitrogen
Min
era
li
Denitrification
obi
liza
tion
zat
ion
Nitrate
(NO-3)
Ammonium
(NH4+)
Nitrifi
cation
Leaching
Modified from the Potash & Phosphate Institute web site at www.ppi-ppic.org
Mineralization Rates (fmin)
Fraction of original organic N available
from N mineralization in each year
Organic Material
Year of
application
1 year after
application
2 years
after
application
cattle (dairy & beef
0.35
0.18
0.09
blood meal
0.65
0.10
0.05
feather or crab meal
0.60
0.10
0.05
sheep and goats
0.30
0.15
0.05
compost (C/N <25)
0.05
0
0
What is the Nutrient Content of Labeled
Fertilizers?
 Expressed as a percent called the “guaranteed analysis” or
fertilizer grade.
 Nutrient content always appears in this order:
- % total nitrogen
- % available phosphate or phosphoric acid
- % soluble potash
 Traditionally, phosphorus and potassium are expressed as their
oxides (P2O5 and K2O).
What Does a Fertilizer Guarantee Mean?
Ag-Gro-Pro
5-10-15
50 lbs.
This bag contains:
5% nitrogen--10% phosphate--15% potash
or
2.5 lbs. nitrogen
5 lbs. phosphate
7.5 lbs. potash
Unlabeled Organic Sources
• published tables of nutrient content
−OK for homeowner
•collect a representative sample
−essential for commercial grower
•obtain a nutrient analysis (“manure”
analysis)
Characteristics of a Sustainably
Managed Soil (Healthy Soil)
•fertile but not excessive in nutrient status
•holds adequate water for plant growth
•allows rainfall or irrigation to infiltrate yet
provides adequate aeration
•has good tilth
•has surface protection
•contains adequate beneficials/minimal
pathogens
Protect the Soil Surface –How?
•protect soil from direct impact of rainfall
−encourage a complete crop
canopy
−mulch
•plant a cool season cover crop
•minimize bare soil all seasons of the
year!
Protect the Soil Surface – Why?
•minimizes erosion & runoff
−strip cropping, contour planting,
intercropping, grassed waterways
•protects soil aggregates
•conserves moisture
•moderates soil temperature
Soil Tilth
•a soil property that assesses the
suitability of soil to support plant growth
•a physical condition of a soil that relates
to its ease of tillage, the impedance of
seedling emergence and root penetration
Practically speaking, what does
good tilth look like?
•compaction is absent in the entire root
zone
•soil does not crust after a rain
•soil is firm when dry and friable
(crumbly) when moist
•drains well after rainfall
Tips for Maintaining Good Tilth
•add organic matter
−food for most soil creatures (heterotrophs)
−amendments
−cover crops**
• warm and cool season choices
•use mulch
−moderates temperature and moisture content
−protects soil from crusting and erosion
•minimize extreme tillage
−rototilling
Are you managing your growing
areas sustainably?
•Are the major macronutrients in the
optimal range based on soil test?
•Is it friable and crumbly when moist?
•Is root growth restricted in the subsoil?
•Does water pond after significant
rainfall?
•Do rills form during rainfall?
Let’s talk about nutrient
management….
Who Needs a Plan?
Any agricultural operation or farm that
•tills, crops, pastures animals, or produces
an agricultural product, and
•has a gross annual income of $2,500 or
more or 8 animal units (1 animal unit =
1000 lbs. of live weight).
What Information Must Be Provided?
•soil tests for each field and pasture
•crops
•manure or compost analysis
•type and number of animals
•amount and type of bedding
•days or hours per day on pasture vs.
confinement
What Information Will I Be Asked
to Provide? (cont.)
•farm map
−Google
−hand drawn is acceptable
•tax account ID numbers
−from tax bill or assessment
What is a Nutrient Management
Plan?
•a written, site-specific plan
•specifies the amount, placement, and
timing of all nutrient applications
(manure, fertilizer, or other nutrient
sources)
Duration of Plans
•Most plans are updated annually;
however, plans can be written to cover a
three-year period under some conditions.
•Soil tests & nutrient source are the
limiting factors
− a soil test is considered current for 3 years
−organic nutrient sources are tested each year
−nitrogen credits are taken for 2 years after
application of organic sources
Where Can I Get a Nutrient
Management Plan?
•Certified Nutrient Management Consultants
−private-sector consultants
−public-sector consultants (University of Maryland
Extension advisors)
•Certified Farmer Operators (CFOs)
−Winter schedule of Farmer Training and Certification
is online
Questions? Comments?
Compaction
•bulk density high enough or pore space
low enough to negatively impact plant
growth
•bulk density >1.6 grams per cubic
centimeter or pore space <40% will
restrict root growth
•information on either is difficult to obtain
Many subsoils in
Maryland’s
Piedmont are
high in bulk
density and low
in porosity