soil health - a root-centric perspective

Soil Health 101

Joel GruverWIU Agriculture

A root-centric perspective

Big Hugh, how long will it take to win the war against

soil erosion?

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

(2008)

> 70

yea

rs la

ter

Reducing erosion rates to T levels is just the beginning of

good soil management.

Well managed soil should deliver nutrients and water to plants when they need them and keep nutrients out of surface and ground water. Well managed soil should

minimize the effects of floods and droughts. Well managed soil should resist compaction and other

forms of degradation.

By focusing soil conservation on enhancing soil function instead of preventing erosion, the goal is

soil improvement as opposed to TOLERABLE DEGRADATION.

Go beyond T - Manage for C!

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

Do you recognize this soil health advocate?

https://vimeo.com/channels/raythesoilguy

Grinnell Heritage Farm, owned and operated by Andy and Melissa Dunham, has grown from three acres in 2007 to 22 acres today and produces more than 60 varieties of certified organic plants and vegetables. The Dunham’s understand that the health of their soil translates into healthier crops and a more resilient farm. A fifth-generation farmer on the Grinnell farmland, Andy has made improving the health of the farm’s soil a major priority. “Our philosophy is feed the soil, it will feed your plants, and then it will feed us,” he said. Read more or watch the three-minute video profile:Grinnell Heritage Farm.       

Do you recognize any of these CC innovators?

Is this really

possible?

Sound management of variable soils

requires a balanced

approach – the causes of

variability can be managed as

well as the effects

WHY?Variation in INHERENT

soil properties

Variation in DYNAMIC

soil properties

Variation in crop

management

Variation in combine operation

Large spatial

variation in crop yield is common

Striping is normally man-made!

Properties

Ephemeral soil properties?

Have you observed this type of contrast on your farm?

Same soil type

Crop field Fence row

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.

Most kits sit idle in closets

A blast from the past

What do the analytical results tell us?

More informed decision making???

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

Soil Health and Soil Quality

are NOT synonymous

Variation in inherent soil properties

≠Soils like cars have inherent

differences that are not changed by normal

management

Thin A

horizon

Thick A

horizon

Ca depleted sub-soil

Ca rich sub-soil

claypan no claypan

USDA Textural triangle

12 textural classes

http://www.oneplan.org/Images/soilMst/SoilTriangle.gif

Texture is generally

considered an inherent soil

property

>12 “10-12”8-10”6-8”< 6”

Variation in texture is directly related to variation in plant available water

Which soil texture holds the most plant available water?

Adapted from Kramer 1983

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

x 0.47 ->x 3.4 ->

In addition to texture, 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.

So how should we target our management

to most improve crop access to water?

x 1.10 ->x 2.5 ->

x 0.88 ->x 0.14 ->

x 0.75 ->x 0.32 ->

Water movement (infiltration vs. run-off) and depth/volume of soil from which crop roots acquire water are much

more sensitive to management than

water holding capacity

Management decisions influence both1)CROP ROOTING POTENTIAL

2) SOIL CONDITIONS

Less of a particular crop/cover crop’s rooting potential is realized when soil conditions impede

root growth and function.

Physical factors – compaction, poor drainage, high or low temperature

Chemical factors – acidity/metal toxicities, nutrient deficiency/excess, salinity

Biological factors – root herbivores/pathogens

Effectiveness of in-field conservation practices should be assessed with respect to impact on root growth and function

NOT tons of soil loss.

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

• Grow strategic sequences of crops/cover crops to maximize a positive cycle of root zone improvement

•Treat seeds/roots with biological inoculants to enhance root-enhancing biological relationships

Acute root

disease

Chronic Root Malfunction

VS.

Chemical, physical and biological factors cause CRM!

is the norm in agriculture

Seed treatments can prevent acute root disease and insect feeding but do not solve the

problem of CRM

STEEP, DEEP and CHEAP Breeding goals proposed by

J. Lynch

RCA = Root cortical aerenchyma

We can breed crops with more

robust roots!

Three primary factors affecting flooding tolerance in plants have been reported: (1) the ability to grow adventitious roots

at the soil surface during flooding; (2) the capacity to form root aerenchyma; and (3) tolerance to toxins (e.g., Fe 2+, H2S) under

anaerobic soil conditions. By analyzing these components separately, it should be possible to perform selections for genotypes exhibiting varying

degrees of flooding tolerance.

Increased efficacy of symbiotic N fixation can be achieved by selecting not only better bacteria but by selecting the best combinations of host plants

and bacteria.

…targeted efforts to select superior plant:microbe partners will bring benefits under a wider range of

environmental conditions.

We are conducting trials of AZ-Green from TerraMax

competition parasitism

antibiosis induced resistance

4 main types of microbial interactions that promote root health

Sales reps should know how their biological

products work

Dramatic effect of the inclusion of compost in

potting media on the health of pepper roots

Aluminum toxicity

Aluminum toxicity

Chemical toxicities inhibit root growth & function

Al toxicity is very common in the SE US and in tropical

countries like Brazil

Nutrient availability affects root growthbut affects top growth more

N and P promote root branching and proliferation

Ontario Ministry of Ag and Food

Why do crops on tiled-drained land tend to be more drought resistant ?

Ontario Ministry of Ag and Food

Do crop roots grow toward water?

Roots elongate directed by gravity in AEROBIC soil!

Air pruning promotes root branching

Soil block system for growing tomato transplants

Air pruning promotes root branching

No root spiraling

Soil can get too hot for optimal

root growth!

Soil aeration also affects soil temperature which strongly affects root growth rate

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

Sub-soil water and nutrients

Compaction strongly impacts root growth and function

Adapted from Hunt et al. (1986)

Tillage can positively and negatively affect

root growth and function

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

Ontario Ministry of Ag and Food

Plow panNetwork of cracks

and biopores

Annual ryegrass roots penetrating > 40”

Radish roots > 40”

after 1.5 months

Land preparation vs.

Soil Preparation

http://www.slideshare.net/pd81xz/ot-b-246

http://www.slideshare.net/pd81xz/ot-b-246

http://www.slideshare.net/pd81xz/ot-b-246

How regularly do you look at roots?

You really won’t know what is happening underground unless you take a look…

All you need is a shop-vac and

a hose :-> !

Its just like going to the dentist!

Healthy shoot growth

and high yields

white color

proliferate in all

directions

extensive growth into the sub-soil

minimal evidence of deformities

Efficient use of soil resources

What should you look for?

Not all healthy roots are white in color!!

How is it possible for healthy crops to grow with such a limited rooting volume?

Wading pools do NOT provide an optimal rooting zone but a small root system can support healthy shoot

growth with ample moisture and nutrition.

?

Mural on my shedinspired by JE Weaver’s illustrations

I have heard people say that horticultural crops just have wimpy inefficient root systems…

http://www.sustainablefarmer.com/pdflibrary/library-rootdevelopment.pdf

Lettuce roots after 3 weeks

The roots on the right were grown in compacted soil, the roots on the left were grown in soil with

good structure.

1ft

Extensive root system

of a flowering lettuce plant

5’

Asparagus root system

after 6 years

10 feet

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

This is not a sandy soil!

http://content.ces.ncsu.edu/vegetable-crop-irrigation

Crop Sensitivity Rooting Impact of drought Moisture to drought Depth Management

Shallow broccolionion

Irish potato

Medium green beansedamame

beet carrot

cantaloupecucumbereggplantpepper

summer squash

Deep lima beans

lettuceokra

parsnippumpkin

winter squashtomato

watermelon

Relative root depths of vegetable crops(according to Dr. Sanders’ bulletin)

Partly a function of length of growing season/timing of harvest

ASM = Available Soil Moisture = % of water between field capacity and wilting point

Key info for scheduling irrigation

Tensiometer

Vegetable crops normally leave more residual N both in crop residues and as mineral N

than grain crops.

While much of this N may be dissipated into the environment before the next crop,

high mineral N (nitrate + ammonium) values are commonly found in the spring after vegetable crops.

Mineral N retained from the previous year is mostly found in deeper soil layers. Therefore, choosing crops with deep root systems is key to utilizing N retained from previous crops.

Large differences in the ability to take up N from deeper soil layers are found among vegetable crops.

0 - 18”18 - 36”36” - 54”

0 55 110 165

Only 55% of N in root zone of following crop

Veg crop sequences with poor N utilization

lbs of N per acre (spring after preceding crop)

Prec

edin

g cr

ops

Follo

win

g cr

ops

Rooting depth

Rooting depth

Rooting depth

http://orgprints.org/256/1/ActaHort_utilising_differences.pdf

0 – 1.5’ 3’- 4.5’1.5’ – 3’

0 - 18”18 - 36”36” - 54”

0 55 110 165

85% of N in root zone of following crop

Veg crop sequences with high N utilizationPr

eced

ing

crop

s

Follo

win

g cr

opsRooting

depth

Rooting depth

Rooting depth

http://orgprints.org/256/1/ActaHort_utilising_differences.pdf

0 – 1.5’ 3’- 4.5’1.5’ – 3’

lbs of N per acre (spring after preceding crop)

What are these crazy people trying to do ?

Location:Laurenburg, NC

Date: 1961

Trying unsuccessfully to change an old highly weathered soil in North

Carolina into a deep fertile “Prairie” soil

http://mnvconsulting.eu/2010/02/05/the-bowmont-catchment-initiative/

The giant plow on the previous slide was designed for burying flood sediment

The advantage of the USGA green is its long-term research-base and proven

performance in the field. If properly built and maintained, golfers rarely face poor

putting conditions. The biggest drawback is collecting the necessary materials and the

cost of construction. One USGA green costs ~$40,000 to construct.

http://www.turspec.com.au/index.php?construction

Sometimes it makes sense to dramatically modify soil inherent properties

The current OM level in a soil is a result of the long-term balance

between organic inputs and outputs

Yield enhancing practices will not build SOM if losses increase at a

comparable rate

Organic outputs

”But with the removal of water through furrows, ditches, and tiles, and the aeration of the soil by cultivation, what the

pioneers did in effect was to fan the former simmering fires… into a blaze of bacterial oxidation and more complete

combustion. The combustion of the accumulated organic matter began to take place at a rate far greater than its annual accumulation. Along with the increased rate of destruction of the supply accumulated from the past, the removal of crops

lessened the chance for annual additions. The age-old process was reversed and the supply of organic matter in the soil

began to decrease instead of accumulating.”

William Albrecht – 1938 Yearbook of Agriculture

Drainage + Tillage + Lime + N + harvest = Accelerated loss of SOM

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.

OM enriched sediment

OM depleted top soil

Redistribution of topsoil is an expensive but potentially highly effective method of improving root

growth and function.

Soil landscape restoration involves moving soil from areas within a field where it has accumulated

through erosion to areas where it has been lost through erosion.

Strategic redistribution of topsoil - ranging from raised beds to reuse of dredge materials - merits

consideration, especially in high value horticultural crop production

Perennial-based rotation systems

Tree cropsPermanent pasture systems

Winter cover crops

Green Lands = Blue Waters

Conservation Cropping Systems

Soil Health is Not an End in Itself

The ultimate purpose of researching and assessing soil health/quality is not to achieve high aggregate stability, biological activity, or

some other soil property.

The purpose is to protect and improve long-term agricultural productivity, water quality, and

habitats of all organisms including people. We use soil characteristics as indicators of soil health, but in the end, soil health must be

identified by how well soil performs its functions.