Soil Health - a root-centric perspective
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Soil Health 101
Joel GruverWIU Agriculture
A root-centric perspective
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Big Hugh, how long will it take to win the war against
soil erosion?
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http://www.swcs.org/documents/filelibrary/BeyondTreport.pdf
(2008)
> 70
yea
rs la
ter
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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.
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Go beyond T - Manage for C!
http://soils.usda.gov/sqi/concepts/soil_organic_matter/som.html
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Do you recognize this soil health advocate?
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https://vimeo.com/channels/raythesoilguy
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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.
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Do you recognize any of these CC innovators?
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Is this really
possible?
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Sound management of variable soils
requires a balanced
approach – the causes of
variability can be managed as
well as the effects
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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!
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Properties
Ephemeral soil properties?
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Have you observed this type of contrast on your farm?
Same soil type
Crop field Fence row
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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.
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Most kits sit idle in closets
A blast from the past
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What do the analytical results tell us?
More informed decision making???
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http://www.swcs.org/documents/filelibrary/BeyondTKarlenSMAF.pdf
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Soil Health and Soil Quality
are NOT synonymous
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Variation in inherent soil properties
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≠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
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USDA Textural triangle
12 textural classes
http://www.oneplan.org/Images/soilMst/SoilTriangle.gif
Texture is generally
considered an inherent soil
property
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>12 “10-12”8-10”6-8”< 6”
Variation in texture is directly related to variation in plant available water
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Which soil texture holds the most plant available water?
Adapted from Kramer 1983
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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
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x 0.47 ->x 3.4 ->
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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?
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x 1.10 ->x 2.5 ->
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x 0.88 ->x 0.14 ->
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x 0.75 ->x 0.32 ->
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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
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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
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Effectiveness of in-field conservation practices should be assessed with respect to impact on root growth and function
NOT tons of soil loss.
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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
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Acute root
disease
Chronic Root Malfunction
VS.
Chemical, physical and biological factors cause CRM!
is the norm in agriculture
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Seed treatments can prevent acute root disease and insect feeding but do not solve the
problem of CRM
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STEEP, DEEP and CHEAP Breeding goals proposed by
J. Lynch
RCA = Root cortical aerenchyma
We can breed crops with more
robust roots!
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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.
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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.
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We are conducting trials of AZ-Green from TerraMax
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competition parasitism
antibiosis induced resistance
4 main types of microbial interactions that promote root health
Sales reps should know how their biological
products work
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Dramatic effect of the inclusion of compost in
potting media on the health of pepper roots
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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
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Nutrient availability affects root growthbut affects top growth more
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N and P promote root branching and proliferation
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Ontario Ministry of Ag and Food
Why do crops on tiled-drained land tend to be more drought resistant ?
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Ontario Ministry of Ag and Food
Do crop roots grow toward water?
Roots elongate directed by gravity in AEROBIC soil!
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Air pruning promotes root branching
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Soil block system for growing tomato transplants
Air pruning promotes root branching
No root spiraling
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Soil can get too hot for optimal
root growth!
Soil aeration also affects soil temperature which strongly affects root growth rate
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Brady and Weil (2002)Brady and Weil (2002)
Sub-soil water and nutrients
Compaction strongly impacts root growth and function
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Adapted from Hunt et al. (1986)
Tillage can positively and negatively affect
root growth and function
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Long term no-till(w/ healthy soil biology) Intensive tillage
Ontario Ministry of Ag and Food
Plow panNetwork of cracks
and biopores
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Annual ryegrass roots penetrating > 40”
Radish roots > 40”
after 1.5 months
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Land preparation vs.
Soil Preparation
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http://www.slideshare.net/pd81xz/ot-b-246
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http://www.slideshare.net/pd81xz/ot-b-246
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http://www.slideshare.net/pd81xz/ot-b-246
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How regularly do you look at roots?
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You really won’t know what is happening underground unless you take a look…
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All you need is a shop-vac and
a hose :-> !
Its just like going to the dentist!
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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?
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Not all healthy roots are white in color!!
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How is it possible for healthy crops to grow with such a limited rooting volume?
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Wading pools do NOT provide an optimal rooting zone but a small root system can support healthy shoot
growth with ample moisture and nutrition.
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?
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Mural on my shedinspired by JE Weaver’s illustrations
I have heard people say that horticultural crops just have wimpy inefficient root systems…
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http://www.sustainablefarmer.com/pdflibrary/library-rootdevelopment.pdf
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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
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Extensive root system
of a flowering lettuce plant
5’
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Asparagus root system
after 6 years
10 feet
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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!
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http://content.ces.ncsu.edu/vegetable-crop-irrigation
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Crop Sensitivity Rooting Impact of drought Moisture to drought Depth Management
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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
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ASM = Available Soil Moisture = % of water between field capacity and wilting point
Key info for scheduling irrigation
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Tensiometer
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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.
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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’
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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)
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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
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http://mnvconsulting.eu/2010/02/05/the-bowmont-catchment-initiative/
The giant plow on the previous slide was designed for burying flood sediment
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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
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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
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”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
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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.
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OM enriched sediment
OM depleted top soil
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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
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Perennial-based rotation systems
Tree cropsPermanent pasture systems
Winter cover crops
Green Lands = Blue Waters
Conservation Cropping Systems
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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.