A root-centric

perspective

Cover Crop Effects

on Soil Health

Managing & Monitoring

WIU AGRICULTURE

Joel

Gruver

Big Hugh, how long

will it take to win

the war against

soil erosion?

Montgomery Cty, IA

> $300 billion in

technical &

financial

assistance

http://www.swcs.org/documents/filelibrary/BeyondTreport.pdf

(2008)

> 7

0 y

ears

late

r

olerable

degradation

We haven’t

won the war

but there is

growing

recognition

that soil

improvement

is a better

goal than

Lookin’ real green in the neighborhood http://talk.newagtalk.com/forums/thread-view.asp?tid=596669

Home of the

Tillage Radish

Major progress has been made in some areas…

…but CCs are used by less than 20% of farmers in most counties

Farmers are at the forefront of

Cover Crop Innovation

Is this

really

possible?

The classification of 60% or more of the sampled pedons

differed from the original. Classification of 15-32% of the

sampled pedons changed at the Order (or equivalent)

level with 11 to 33% of the pedons originally classified as

Black soils (i..e. Mollisols, Chernozems…) no longer

classified as Black soils

This is going in the wrong direction!

Soil Changes After Sixty Years of Land Use in IowaJessica Veenstra, Iowa State University, 1126 Agronomy Hall, Iowa State

University, Ames, IA 50010

Soils form slowly, thus on human time scales, soil is essentially a non-

renewable resource. Therefore in order to maintain and manage our limited

soil resources sustainably, we must try to document, monitor and understand

human induced changes in soil properties. By comparing current soil

properties to an archived database of soil properties, this study assesses

some of the changes that have occurred over the last 60 years, and attempts

to link those changes to natural and human induced processes. This study

was conducted across Iowa where the primary land use has been row crop

agriculture and pasture. We looked at changes in A horizon depth, color,

texture, structure, organic carbon content and pH.

Hill top and backslope landscape positions have been

significantly degraded.

Catchment areas have deeper topsoil.

-> significant loss of

productivity

-> little gain in

productivity

This past fall, students in my Soil Properties class brought in paired

(Crop field & Fence Row) soils from their family’s farm. In most cases,

the fence row soils had higher carbon dioxide and ammonia production.

What do the analytical results tell us?

More informed

decision making???

Informed decision making requires regional calibration!

Consistent depth of sampling is important!

In essentially all cases where conservation

tillage was found to sequester C, soils were

only sampled to a depth of 30 cm or less…

Sometimes the story

changes with depth

of sampling

Hayfield

~ 5 yrs

ago

Slabaugh Farm

Goshen, IN

Former

hayfield Even more

perplexing

Uniform

management for

> 40 years

Smith Family Farms - KS

Former

hayfieldIntensive soil

sampling has

not explained

the consistent

difference in

productivity

Smith Family Farms - KS

Farmers want to understand

what yield maps are telling

them about their soils

Some yield

variability is

easy to

explain

Pattern

tiling

The main factor

driving yield variation

in this field is

BELOW the plow layer!

Maybe

we need

to take a

deeper look

@ soil health

It is becoming clear that root traits are

important drivers of many ecosystem

processes such as C and nutrient

cycling and the formation and

stabilization of soil structure

Bardgett et al.(2014)

In this review, we propose the use of suitable plant

species, termed primer-plants, for the primary

purpose of preparing soil conditions for the benefit

of following crops.

Proportions of roots of the current crop

recolonizing root induced macropores (RIMs) of

the previous crop averaged 18% for corn after

corn, 22% for alfalfa after corn and 41% for corn

after alfalfa…

Our data suggest that surface mulch and deep root

channels left by winter cover crops can be

advantageous for summer crop growth, particularly

when soils are highly compacted. Tap-rooted forage

radish and rapeseed cover crops enhanced corn

root access to subsurface soil water by providing

deep root channels in compacted soils

soil penetration capabilities

radish > rapeseed > rye

“Within 2-4 weeks we began to see the ryegrass extract

break down the fragipan… not only does ryegrass have a

deep root system that can penetrate the pan, but it also

releases a chemical or chemicals that can help break it”

– AD Karathanasis

Impact of preceding cover crops

on cash crop root density

Chen and Weil (2011)

Soil moisture sensors

showed more rapid water use

by corn roots (and more

rapid recharge of soil

moisture after rains) in the

subsoil of plots previously

growing forage radish

compared to plots previously

growing rye or no cover crop.

In contrast, the rye cover provided more residue mulch

than the radish and so conserved more water in the

surface soil above the plow pan.

Soil/crop management systems

impact the 1) movement of

water, 2) storage of water, and

3) volume of soil from which

crop roots acquire water and

other resources.

How should we target our management

to most improve crop access to water?

Predicted Soil

Hydrologic Properties

The calculator predicts

soil hydrologic

properties based on

soil texture as well as

modulating factors:

OM, salinity, gravel

content and

compaction

Based on data from

~ 2000 soil samples

+ 10%

+ 150%

- 14%

- 86%

Water movement

(infiltration vs. run-off)

and depth/volume of soil

from which crop roots acquire

water and other resources

are much more sensitive to

management than

water holding capacity

Kautz et al. (2012)

A conceptual model of nutrient acquisition from the SUBSOIL

Subsoil

supplies more

than water

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

Sub-soil water

and nutrients

Compaction strongly impacts root growth and function

Least Limiting Water Range

dry Soil water content, cm3/cm3 *100 wet

20 25 30 35 40 45 50 55

LLWR for loose well-aggregated soil

LLWR for compacted soilNot

enough O2

for root

respiration

Soil too

hard for

roots to

penetrate

Ray Weil

Compacted soils are

more easily penetrated

when wet BUT only

some CC species can

tolerate wet soils

Annual ryegrass is

very tolerant of

wet soil conditions

Brassicas are not!

Many of you are

probably familiar with

the extraordinary

root illustrations by

John E.Weaver

Depth (ft) %sand %silt %clay

0-0.5 31 34 35

0.5-1 33 29 38

1-2 23 31 47

2-3 20 31 49

3-4 22 34 44

4-5 25 37 37

Soil particle size variation with depth at

Dr. Weaver’s research farm (Lincoln, NE)

Deep rooting in this soil

required excellent structure!

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

Ontario Ministry of Ag and Food

Plow pan

Network

of cracks

and

biopores

Different species

of worms make

different types of

biopores!

more roots

+ more worms

-------------------

more biopores

Soil/crop management strategies

for optimum root growth and function

• Alleviate existing physical, chemical and/or biological

barriers to root growth

• Prevent development of physical, chemical and/or

biological barriers to root growth

• Plant crops on soils for which they are well adapted

•Treat seeds/roots with biological inoculants to enhance

root-enhancing biological relationships

•Grow strategic sequences of crops/cover crops to

maximize a positive cycle of root zone improvement

Perennial-based

rotation systems

Tree cropsPermanent pasture systems

Winter cover crops

Green Lands = Blue Waters

Conservation

Cropping Systems

The best

way to grow

biopores!

Go beyond T - Manage for C!

http://soils.usda.gov/sqi/concepts/soil_organic_matter/som.html

D

Go beyond T - Manage for C!

http://soils.usda.gov/sqi/concepts/soil_organic_matter/som.html

DEPTH!

Effectiveness of conservation practices

should be assessed with respect to

impact on root growth and function

NOT tons of soil loss.

I encourage all of you to think deeper

New methods and

new priorities can

provide an invaluable

ROOT’S EYE VIEW

of soil health