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Soil structure – the key dynamics
Tim Chamen
CTF Europe
How do we protect our soils?
Stock problems
How do we protect our soils?
Machinery problems
Protection measures
• Knowledge – understanding how soils work
• the role of organic matter
• the role of water
• soil compaction
• Care – acknowledging soils’ crucial importance
– attending to detail
– whole farming system approach
Soils around Worfield
Machinery Work Days with season
MWD Wet Normal Texture Notes
Salwick (572m) 53 82 Fine and coarse loamy Some seasonal water-logging but also droughty
Bridgnorth (551a)
76 106 Sandy and coarse loamy Easily worked soils but droughty
Newport 1 (551d)
102 122 Medium sandy Easily worked but very droughty
Rivington 2 (541g)
52 82 Loamy brown earths Mixed cropping, well drained but slightly droughty
The role of soil water
With acknowledgement to R.C. Palmer, Independent Soil Assessment Specialist [email protected]
The volume of soil that we can influence
Examples of good & poor soil structure
Good
Poor in parts
Examples of good & poor soil structure
Reasonably good
Very poor
Examples of good & poor soil structure
Good
Poor
Examples of good & poor structure
Good
Poor
How do we improve soil structure?
• Increase organic matter levels
• Avoid stresses on the soil:
– compaction
– tillage
– starving wildlife
• bare fallows – at any time
– raindrop impact
• Grow good crops
The importance of SOM!
• Without soil organic matter (SOM), soils have no structure or life
– SOM is the primary food source for all soil living animals and micro-organisms
– SOM initiates aggregation of soil particles and thus porosity
– Animals and roots create further porosity
The dynamics of SOM
• Plants add SOM
• Soil micro-organisms break it down
• Addition or loss of SOM is the balance of these two processes
• “Inappropriate” tillage increases loss by exposing more of the soil to microbes
+ -
+ -
The Carbon Cycle
Increasing SOM
• There is no controversy about increasing SOM
– it is beneficial on practically all levels
Addition of SOM
• High yielding crops
• Manures
• Composts
Addition of SOM
• Cover crops
–with large vigorous roots
– as much growth and over as long a time period as possible
Loss of SOM
• Vigorous tillage in poor soil conditions
Loss of SOM
• Whole crop removal
• only cover cropping has any chance of maintaining status quo
Freely available soil maps Soil texture, pH, SOM, nutrients etc.
Worfield
The role of soil water
With acknowledgement to R.C. Palmer, Independent Soil Assessment Specialist [email protected]
The volume of soil that we can influence
Effect of moisture content on soil strength – at a given density
Effect of moisture content on different soil types
(after Whalley et al., 2004)
Silty clay loam
Loamy sands
Water dynamics
Effect of poor water dynamics!
Might only be topsoil effect
Effect of “aeration”
Compaction stops water getting into soils
After: Chyba, 2012
Effects of compaction on water infiltration - Cambs
Effects of compaction on water infiltration - Cambs
10 mm.h-1 rainfall intensity on a 600 mm wide tramline track with zero infiltration, equates to 10 litres min-1 100 m-1 the amount of which is illustrated above
Infiltration where there was an obvious wheeling at or
prior to sowing was almost zero
Infiltration a few metres away where crop was growing
evenly was orders of magnitude greater with all
water seeping away within 60 seconds
Effect of soil structure on drainage
• A practical demonstration
The effect of pore size on water retention
Effect of pore size on water retention
Hinge – narrow end
Water drainage
Difference between good and poor structure
Adjacent fields in no-till for 3 years
First video, random traffic no-till
Second video, controlled traffic no-till
Effect of compaction on seedbeds
Compaction is one of our biggest enemies
Effect of compaction on seedbeds
• Energy to loosen. Energy to re-compact
• Loss of moisture
• Uneven germination and growth
– Timeliness effects on subsequent chemical applications
Causes and susceptibility to poaching
• Type and number of grazing animals • Climate, principally the frequency, duration and
intensity of rainfall and evaporation • Plant cover and grass species • Soil strength, controlled by texture, structure, pore
space and hydraulic conductivity • Interactions between these:
– principally the role of plants in determining soil strength – soil/climate interactions in determining soil water content
Damage primarily confined to the top 10 cm of soil
Avoidance: attention to detail
Aeration to alleviate poaching
Is compaction repaired naturally?
Remoulded samples left from
October – March 5 cm deep in the soil
Little sign of any
change over winter!
Take home messages
• Good soil structure throughout drained profile vital for good soil function
– infiltration
– drainage
– ease of seedbed production
– lower energy costs
– greater plant available water
– higher crop yields
Take home messages
• Good structure enhanced by:
– increased soil organic matter
• high yielding crops
• residue retention
• perennial crops
• cover crops to fill a seasonal gap
• less tillage – particularly rigorous tillage in poor conditions
– reduced compaction
• low ground pressure
• controlled traffic
Take home messages
• For healthy soils:
– Grow high yielding crops
• chicken and egg – need a healthy soil!
– Reduce tillage
• compaction increases the need for tillage
– Manage compaction
• create a wider window of opportunity
• pay close attention to tyres
• consider controlled traffic
Take home messages
• Compaction is one of our worst enemies:
– increases energy requirement for cultivation
– results in poor seedbeds
– soils don’t recover much from it over-winter
Harvesting is a lottery!
Example of OutTrac for maize
6 m, 9 row maize planter, 0.67 m rows
3.35 m harvester track gauge
2.01 m tractor track gauge
OutTrac CTF System
TwinTrac 4.8/24 m system for maize
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