The hidden half of agriculture
How many of you regularly
look at crop roots ?
John McGillicuddy
Bill Darrington (Persia, IA)
All you need to do is use rootworm resistant genetics… right??
When rootworm pressure is high, rootworm resistant
genetics normally result in much healthier roots
Rootworm resistant genetics are not a silver bullet !
Severe damage by corn
rootworm larvae to roots of
a biotech corn rootworm
hybrid
http://www.ipm.iastate.edu/ipm/icm/2006/11-13/btcorn.html
Seminal roots cease new growth shortly after the
coleoptile emerges from the soil surface. The nodal root
system becomes visible at ~ V1. The nodal root system
becomes the dominant system by V6.
16
4 weeks
8
7 feet deep !!
1926
?
PLOW PAN
Compacted
layers
can
Sub-soil water
severelyand
limit
root growth
nutrients
Brady and Weil (2002)
Adapted from Hunt et al. (1986)
Long term no-till
Intensive tillage
Plow pan
Ontario Ministry of Ag and Food
(w/ healthy soil biology)
Network
of
biopores
Which solution
would you use ?
WIU Allison Organic Research Farm – September 2007
Please plant me no-till
next spring !!
January
Visual evidence of biodrilling
Canola root
Rapeseed root
The experiment was planted to
corn on May 29 2008
Corn following radish established
well and had the lowest weed
pressure in the row.
Maybe you should come out to
the farm and see how things
look this fall…
Chemical toxicities
can inhibit root growth
Aluminum
toxicity
Aluminum
toxicity
Galled root system of tomato infected with root-knot
nematode, Meloidogyne sp., compared with noninfected root system
Root pathogens can
Root knot juvenile penetrating a tomato root
inhibit root growth
http://www.agnr.umd.edu/users/nrsl/entm/nematology/images/eis143.jpg
You won’t know what is happening
underground unless you take a look…
Roots have many functions !
Absorptive network for limiting soil resources
of water and nutrients
Mechanical structures that support plants,
strengthen soil, construct channels, break
rocks, etc.
Hydraulic conduits that redistribute soil water
and nutrients
Habitats for mycorrhizal fungi, rhizosphere
and rhizoplane organisms
Carbon pumps that feed soil organisms and
contribute to soil organic matter
Storage organs
Chemical factories that may change soil pH,
poison competitors, filter out toxins,
concentrate rare elements, etc.
A sensor network that helps regulate plant
growth
http://www.sparknotes.com/biology/plants/plantstructures/section2.rhtml
http://www.sparknotes.com/biology/plants/plantstructures/section2.rhtml
The movement of fluids from the root hairs to the xylem
can occur through one of two conductive pathways–
the apoplast and the symplast.
The apoplast route consists of inter-cellular spaces
within the root cortex along which water and solutes
can diffuse.
The symplast route consists of channels through cells
along which water and solutes are actively transported.
The cell wall of the endodermis (pink inner strip of cells) is waterproofed by the
suberised Casparian strip, which forces water to enter the symplast before it can
enter the root xylem
http://www.mie.utoronto.ca/labs/lcdlab/biopic/fig/35.03.jpg
Water moves upward
through plants
whenever there is a
progressively more
negative gradient of
water potential along
the soil-plantatmosphere
continuum
H20
A continuous
chain of water
molecules is
pulled up
through the
plant
H20
H20
H20
Solar energy
drives the
process
Plants provide
the conduit
Understanding nutrient uptake
H 20
Root growth
N, S, P
Root exudates
activate soil microbes
Transpirational
stream
H 20
Diffusion
Nutrient uptake is an active and selective process
Rhizosphere
Roots normally
occupy < 1% of topsoil
volume
The rhizophere is
normally < 10 % of soil
volume
Zone of root
influence
Navigating the rhizosphere
End of the
rhizosphere
Rhizoplane
Microbial activity
EndoRhizosphere
Ecto-Rhizosphere
< 10% of soil
volume
> 90%
of soil
volume
A few millimeters
(Lavelle and Spain, 2001)
Both
strategies
important
!
Feed
the
soil vs.are
Feed
the crop
Healthy roots
available inefficiently…
nutrients !
Unhealthy
rootsneed
use nutrients
Acute
root
disease
Chronic root
malfunction
Healthy
cowpea
nodule
with a
pink
interior
Mycorrhizal associations
Ectomycorrhizae
AM endomycorrhizae
Arbutoid
mycorrhizae
Ericoid
endomycorrhizae
Orchid endomycorrhizae
Lavelle and Spain (2001)
Mycorrhizal Networks: Connecting
plants intra- and interspecifically
•Many plants are
connected
underground by
mycorrhizal hyphal
interconnections.
•Mycorrhizal (AM)
fungi are not host
specific.
Illustration by Mark Brundrett
Ectomycorrhizal roots
Close up of ecto-mycorrhiza
Increase nutrient (P) uptake
suppress pathogens
Mediate plant competition
Improve soil structure
Glomalin
Superglue
of the soil ??