Soil and Plant Basics
Nitrogen Cycling
Doug Shoup
KSU Southeast Area Agronomist
dshoup@ksu.edu
620-212-2399
What is Soil?
Mineral
- Sand, Silt, Clay
Pore Space
25%
Water
25%
Organic Matter
Organic
Matter
5%
-Decomposed Plants
- Decomposed Microorganisms
-Decomposed Animal Material
Mineral Matter
45%
Soil Formation
• A fully developed soil has
three horizons: A, B, C
Surface Soil - Zone of maximum
organic matter accumulation and
leaching
Subsoil - Zone of maximum
accumulation of clay, iron, lime and
aluminum. Lighter in color than surface soil.
Parent Material - Geological material
such as loess or glacial till similar to the
original material from which A and B
horizons developed.
Bedrock - Varies greatly in
and depth.
thickness
Distribution of Parent Material
Soil Microorganisms
• Decompose organic materials
• Crop residues
• Organic chemicals
• Diseases
• N fixation in legume crops (Rhizobium)
• Mineralize and immobilize nutrients
Inorganic nutrients
Organic nutrients
Mineralization
Plant Available
Form
Plant Unavailable
Form
Immobilization
Soil Physical Properties
Affecting Soil Productivity
Dr
a
ina
Depth of
Rooting Zone
ge
Color
Soil Productivity
e
p
o
Sl
Permeability
e
r
tu
c
ru
t
S
Texture
Po
ro
sit
y
Soil Structure
• The arrangement of soil particles into larger
units
• Structure affects soil permeability, porosity
and root growth
• Affects resistance to surface crusting
Structure is destroyed by ?
Structure is improved by ?
Soil Porosity and Permeability
• Porosity is the total amount of pore space in the soil
(30 to 60%)
• Affects the storage of air and water
• Affects the rate of movement of air and water
• Permeability is the ease in which water, air, and plant
roots move through the soil
• Ease of air, water and root movement
• Affects rate of water intake and drainage
• Porosity and permeability are affected by soil texture,
structure, organic matter and compaction
Soil Water
AVAILABLE SOIL WATER: water held by capillary forces
between field capacity and permanent wilting point.
Saturation
Field Capacity
Permanent Wilting Oven Dry
Point
Available Water
Water holding Capacity as Affected by
Soil Texture
Inches water/ft. soil
5
d
Fiel
4
ity
c
a
Cap
3
A
2
1
ter
a
W
e
l
lab
i
a
v
ne
a
m
Per
Sand
ting
l
i
nt W
Sandy Loam Silt Loam
ge
a
t
n
e
Perc
Clay Loam
Clay
Soil Nutrients
Essential Nutrients
Thirteen essential nutrients
– Nitrogen, phosphorus, potassium, calcium,
magnesium, sulfur
– Iron, manganese, boron, molybdenum,
copper, zinc, and chlorine
Micros are needed in much lower
concentrations to ensure adequate
supply
Organic Matter
Important source of many nutrients.
Simple organic compounds as chelates.
S, Zn and B deficiencies are more likely to
occur in soils low in O.M.
Nutrient credits from OM.
Soil pH
Soil pH affects availability of nutrients.
In general the solubility and availability of
nutrients are greatest in acid soils and
lowest in high pH calcareous soils.
Effect of Soil pH on Nutrient Availability?
Nitrogen
Nitrogen functions in the plant
Proteins
Chlorophyll
Enzymes and other compounds
Necessary for respiration, growth and reproduction
Nitrogen fertilization
Required in largest quantities and most frequently deficient
Increased forage yield and quality of nonlegumes
Improved root growth and H2O use efficiency
Forms used by plants as
NO3 - Nitrate
NH4+ Ammonium
Mineralization
• Soil Organic Matter
– Source of most soil N
– 5% N, 1-3% released annually
• 10-30 pounds N per year per 1% OM
• Rate of release affected by:
– Temperature
– Moisture
– Previous plant types (legumes)
– Past N inputs
• Organic N converted to inorganic N
What Happens to Inorganic N?
Ammonium NH4+
• Utilized by plant
• NH4 to organic forms
– Ammonification
• Converted to NO3
• Converted to NH3
– Volatile losses
Nitrate NO3• Utilized by plant
• NO3 to organic forms
• Leaching
– Loss deep in soil profile
• Denitrification
– Loss in saturated soils
NO2-
N2
Manure
• Animal manure is an excellent
source of nutrients
• Highest nutrient content is generally
in poultry litter
–
Beef manure more readily available
• Sample for nutrients
–
–
Representative sample
Dry matter important
Beef Manure
Representative Analysis of Beef Manure Systems (MF2562)
Solid Manure Analysis (lbs/ton)
Bedding
or Source
% Dry
Matter
Total N
NH4
Total P
Total K
No
15
11
4
7
10
Yes
50
21
8
18
26
Pit
11
40
24
27
34
Lagoon
1
4
2
9
5
Beef Manure Nitrogen
• Nitrogen in manure is consists of:
– Organic N
– Inorganic N
• Organic N is slowly released
– Beef manure ~65% of N is in organic form
– 1/4th available 1st year (1/8th & 1/16th in year 2&3)
• Inorganic N is immediately available
– Beef manure ~35% of N is in inorganic form
– Predominantly ammonium (NH4)
What About Manure Inorganic
Nitrogen?
• About 35% of the nitrogen is inorganic
– Mostly in the NH4 form
– Readily available to plant, but some is subject to
losses
Manure Ammonia
Volatilization
Nitrogen and Rainfall
Function of lightning converting N2 gas to
NO3 and deposited by rainfall
Mostly by thunderstorms
Very little by snowfall
3 to 10 lbs of N per acre per year
Unimportant over the short term but very
important over hundreds of thousands of
years
Legumes
• Symbiotic Fixation
– Alfalfa, clover, beans, etc.
– Symbiotic relationship with
Rhizobiumbacteria
– Plant provides energy
(carbohydrate)
– Bacteria synthesize N2 to
NH4
Benefits of Legume in Grass
• Even though legumes don’t feed N to grass,
there is still a benefit to interseeding in
fescue
– Reduced fertilizer costs
– Potential increase forage
– Cattle gains
– Grazing season distribution
– Reduce endophyte toxicity
in high endophyte fescue
Grazing Endophyte Fescue
Mound Valley, Seeded 1990 and grazed
from 1993 - 1995
Average Daily
Gain
lb/head/day
Endophyte Fescue + Nitrogen
1.28
Endophyte Fescue + Ladino clover
1.60
NonEndophyte Fescue + Nitrogen
1.67
NonEndophyte Fescue + Ladino clover
1.78
Coffey, Moyer, and Brazle
Plant Growth and
Development
Plant Growing Points
Monocots
Grasses, Sedges
Dicots
Broadleaves
Grass Grows from Here
Tiller
Growing
Points
Crown
Growing
Points
Node
Growing
Points
Crown
Growing
Points
wu11
Root Hair
• Root hair are the main sorce
for water and nutrient
absorption
– Surface area!
Water
Nutrients
Slide 32
wu11
A root hair is an extension of a single cell. Root hairs usually only live a couple of days though they may live as long as a week.
Ward Upham, 9/5/2008
Depth of Rooting Zone
Crop
Rooting
Depth
Major Feeding
Zone
Alfalfa
20 ft. +
50% in top 3.5 ft.
Bromegrass
5.5 - 6.5 ft.
75% in top 3.5 ft.
Wheat
4 – 6 ft.
80% in top 3 ft.
Corn
4 - 7.5 ft.
75% in top 2 ft.
Grain Sorghum
4.5 - 6 ft.
75% in top 3.5 ft.
Weaver, Root development of field crops
Connecting Roots and Leaves
Grasses
• Xylem: Carries water and
nutrients from the roots to Phloem
other parts of the plant.
Xylem
• Phloem: Carries sugars
and other carbohydrates
from the leaves to other
parts of the plant.
Other Plants
Cambium
Xylem
Phloem
Xylem
Phloem
Water Flow and Usage
Cooling of leaves (and
atmosphere)
Sugars
produced
in leaves
Water and
Nutrients
About 90% of the
water flowing
through the plant
is used for
transport-not for
plant reactions.
Stomate
Guard Cells
Epidermal cells
Photosynthesis
Photo=light
Synthesis=making something
sunlight
CO2 + H20
carbon dioxide
CH2O + O2
water
sugar
chlorophyll
oxygen
Root, Stem, Leaf Relationship
• 95% of plant food is taken from
the air
– Leaves are Food Factories
• 5% of plant food is taken from
the soil
– Roots gather raw materials (water,
nutrients) which are converted into
plant food by the leaves
• Overgrazing will destroy both
the leaves and the roots
Grass Anatomy
Iowa State University Extension PM 1791
Legume Anatomy
Iowa State University Extension PM 1791
Forage Development
• 3 primary stages of forage development
1. Vegetative
Forage Development
• 3 primary stages of forage development
1. Vegetative
2. Elongation/Jointing
Forage Development
• 3 primary stages of forage development
1. Vegetative
2. Elongation/Jointing
3. Reproductive
Plant Growth Rate
Iowa State University Extension PM 1791
Native Grass Yield vs. Maturity
Baker et. al, 1999
A Balanced Forage System
Clover
CS Annual
Forage Yield
CS
Perennial
WS Annual or
Perennial
Feb
Apr
Jun
Aug
Oct
Dec
Questions?