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

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

Rootworm resistant genetics are not a silver bullet !

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.

4 weeks8 weeks16 weeks

7 feet deep !!

1926

?

Brady and Weil (2002)Brady and Weil (2002)

PLOW PAN

Compacted layers can severely limit root growth

Sub-soil water and nutrients

Adapted from Hunt et al. (1986)

Long term no-till(w/ healthy soil biology) Intensive tillage

Ontario Ministry of Ag and Food

Plow panNetwork

of biopores

Which solution would you use ?

WIU Allison Organic Research Farm – September 2007

January

Please plant me no-till next spring !!

Visual evidence of biodrilling

Rapeseed root

Canola 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…

Aluminum toxicity

Aluminum toxicity

Chemical toxicities can inhibit root growth

http://www.agnr.umd.edu/users/nrsl/entm/nematology/images/eis143.jpg

Galled root system of tomato infected with root-knot nematode, Meloidogyne sp., compared with non-

infected root system

Root knot juvenile penetrating a tomato rootRoot pathogens can inhibit root growth

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 morenegative gradient of water potential along the soil-plant-atmosphere continuum

H20

H20

H20H20

A continuous chain of water molecules is

pulled up through the

plant

Solar energy drives the process

Plants provide the conduit

Understanding nutrient uptake

Transpirationalstream

H20

H20

Root exudatesactivate soil microbes R

oo

t gro

wth

N, S, P

Diffusion

Nutrient uptake is an active and selective process

Rhizosphere

Zone of root influence

The rhizophere is normally < 10 % of soil volume

Roots normally occupy < 1% of topsoil volume

Navigating the rhizosphere

RhizoplaneEndo-

Rhizosphere Ecto-Rhizosphere

End of the rhizosphere

(Lavelle and Spain, 2001)

< 10% of soil volume

> 90% of soil

volume

Mic

rob

ial

acti

vity

A few millimeters

Acute root

disease

Feed the soil vs. Feed the crop Both strategies are important !

Healthy roots need available nutrients !Unhealthy roots use nutrients inefficiently…

Chronic root malfunction

Healthy cowpea nodule with a pink

interior

Ectomycorrhizae

Arbutoid mycorrhizae

Ericoid endomycorrhizae

Orchid endomycorrhizae

AM endomycorrhizae

Mycorrhizal associations

Lavelle and Spain (2001)

•Many plants are connected underground by mycorrhizal hyphal interconnections.

•Mycorrhizal (AM) fungi are not host specific.

Illustration by Mark Brundrett

Mycorrhizal Networks: Connecting plants intra- and interspecifically

Ectomycorrhizal roots

Close up of ecto-mycorrhiza

Increase nutrient (P) uptake suppress pathogens

Mediate plant competition Improve soil structure

GlomalinSuperglue of the soil ??

Roots are worth

a closer look !