Q & A – Soils and Soil
Fertility
Trish Steinhilber
psteinhi@umd.edu
Master Gardeners’ Advanced Training
June 2015
biomass
organic residues
solids and
by-products
soil solution
soil air
pore space
humus
primary
minerals
inorganic
solids
secondary
minerals
Organic Matter
Humus
75%
10%
Biomass
15%
Residues &
By-Products
Department of Environmental Science and Technology
Growth Factors:
What do plants need to grow?
1. water
2. oxygen
3. heat
4. carbon dioxide
5. mechanical support
6. nutrients
Soil Aeration - The exchange of O2 and
CO2 between the soil pores and the
ambient atmosphere
Hillel
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
Balance Between Water and Air
• 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 form most plants can use
• micropores (very small pores)
−water is held too tightly to be used by most plants
−refuge of soil organisms when soils dry out
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
Soil Texture and Cation Exchange Capacity
Soil Texture
Cation Exchange Capacity
cmolc/kg
sands
fine sandy loams
loams and silt loams
clay loams
clays
1-5
5-10
5-15
15-30
>30
What is a fertile soil?
•one that provides an adequate supply of all
nutrients throughout the entire growing
season
•test soil
− Is soil too acidic for plants being grown?
− Are major nutrients present in adequate supply?
− Lime first, then add other nutrients if needed.
soil acidity:
the adverse
condition in the
soil solution in
humid regions
Too much or too little ….
•Is too much of any nutrient bad for
plants?
•Is too much phosphorus bad for plants?
•Is too little of a nutrient bad?
Soil Tests and Their Interpretation
Soil Test Category Interpretation
very low, low
nutrient will, in all likelihood,
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
Lowering Phosphorus Soil Test Levels
•possible
•not needed
•not ethical (personal opinion)
What Nutrient Source Should Be
Used?
•most organic sources are mixtures of N,
P and K
•appreciate single source fertilizers
−ammonium sulfate, urea
−triple superphosphate
−muriate of potash
Composting Organic Materials
•thermophilic, aerobic process which
changes readily-decomposable
compounds to more stable compounds
−humus-like end product
•requires the correct mixture of starting
materials
−brown (high C/N) and green (low C/N)
−requires aeration
How Does Composting Alter an
Organic Material?
•ammonium and nitrate virtually disappear
•virtually all of the nitrogen is organic
nitrogen
- N is released more slowly in composts than in
feedstock materials
•low in pathogens; friable and crumbly;
pleasant, earthy odor
Poultry Litter from Delmarva
(Preusch)
Type
Soil Texture
fresh
sandy loam
Mineralization
Rate
.42
composted
sandy loam
.085
fresh
clay
.35
composted
clay
-.055
Mineralization Rates of Meat & Fish
Processing Residuals (f-min)
Material Type
blood meal
feather meal
hydrolyzed
fresh
pelletized fish byproduct
* fraction of original organic N
Year of application
0.65 - 0.70
0.60 - 0.65
0.10
0.93
Mineralization Rates of Yard Waste
and Composts (f-min)
Material Type
Huck’s Hen Blend (VA)
Year of application
0.002
(8 parts yard waste - 1 part hen
manure, C/N = 29)
Panorama Pay Dirt (VA)
0.05
(1 part yard waste - 2 parts
poultry litter, C/N = 18)
grass clippings (NJ)
* fraction of original organic N
0.25 (scl)-0.40 (sl)
Mineralization Rate Composts (f-min)
Material Type
Year of application
Bovung1
-0.02
Fertilife1
-0.02
Erth-rite-C1
0.05
on-farm sheep manure &
house-hold vegetable waste
compost
-0.05
* fraction of original organic N, 1 Douglas and Magdoff
Gutser et al., 2005, J. Plant Nutrition and Soil Science
Protect the Soil Surface (esp. in fall)
•minimizes erosion
•protects soil aggregates
•conserves moisture
•moderates soil temperature
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!
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
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
Questions?
•www.extension.umd.edu/anmp
−“Workshop Tools” tab
• Soils (Basic) cell