N Heath Soil Health in the Subsoil

“What lies beneath the vine”
Soil health in the subsoil
Nathan Heath
Certified Professional Soil Scientist
Murray CMA
Introduction
• Look at the soil beyond the topsoil
Soil health - we influence
this zone through our
management (0-30cm)
The subsoil plays a very important role in
determining soil productivity, versatility and
suitability for vine growth. However significant
changes to the subsoil properties are generally cost
prohibitive or technically infeasible and therefore we
must adapt our management to the match soil
capability
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Why?
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•
•
•
•
•
Vineyard variability often caused by soil factors
Climate change, input costs
Water issues – availability, cost, quality & quantity
Off-site impacts – erosion / run-off
Management induced changes
Precision management to minimise variation
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Vine management – pruning (bud numbers)
Irrigation scheduling
Fertiliser application
Harvesting options
So what are the issues
• Locally ??
• Chemically
– pH (acidity or alkalinity)
– Salinity / sodicity
– Nutrient availability – too much (B, Al, Na) or too little
• Biologically
– Pest and diseases
– Mycorrhizal colonisation
– Sufficient biological fertility for a healthy functioning soil
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http://www.dpi.vic.gov.au/dpi/vro/vrosite.nsf/pages/soil_mgmt_subsoil
Subsoil investigation
• Measuring and monitoring
– Soil testing (deep sampling)
– Penetrometers
– Soil health monitoring kits
– EM38 / ground penetrating radar
– Direct observation of soil pits (added advantage
of looking at root health & vigour)
– Yield, quality, vine appearance etc
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Subsoil examination
•
6 key soil properties
1. Colour (matrix colour, presence of mottling, gleying, bleached
horizons etc)
2. Texture (sand, silt, clay, buckshot, gravels)
3. Depth (total depths – soil, topsoil, rooting depth, horizon boundaries,
abrupt, diffuse etc)
4. Soil structure (type & degree of structure, soil structure stability, soil
strength)
5. Plant root growth (depth, extent, indication of barrier, growth habit,
lesions & malformations)
6. Soil pH & CaCO3 (using a soil kit)
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•
Used individually or collectively to provide an indication of
likely soil processes
Remember to observe holistically (landscape & whole soil)
Water availability
• Available water (ex irrigation) =
– Rainfall / Evapotranspiration
– Rooting depth
– Soil water holding capacity
• Soil water holding capacity =
– Soil texture
– Presence of gravels
• Texture x (%) gravels x rooting depth
– Sandy loam x 20% gravels x 90cm rooting
depth
150 (mm/m texture) x 0.8 (stone free soil) x 0.9 (root depth) = 108mm WHC
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Available water holding capacity (mm/m) of
different textured soils
200
180
140
120
100
80
60
40
20
0
Sand
Sandy
loam
Silt loam
Clay loam Silty clay
Clay
Texture
Landon J R - Booker Tropical Soil Manual
Water holding capacity (mm / m) of a silt loam soil
with differing gravel content
200
180
160
WHC (mm/m)
AWC (mm/m)
160
140
120
100
80
60
40
20
0
0
10
25
50
70
90
% Gravels
Landon J R - Booker Tropical Soil Manual
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Mechanical impedance
• Indicators of impedance
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Soil structure
Structure stability
Presence of hardpans & compacted layers
Soil strength differences (penetration resistance)
Soil textural differences
• Depth of soft soil (<2 MPa) 24 hrs after irrigation
Wheaton et al (2008). Management to increase the depth of soil improves soil conditions and grapevine performance in an
irrigated vineyard. Soil & Tillage Research 98 p68-80
• Root growth
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Soil structure - aggregate stability
Dispersion
Normal aggregation
Slaking
Root Growth
• Plant hormones synthesised by roots promote growth of
shoots – size and vigour of root system influence canopy and
vice versa, but not always – root functioning important
• Root growth
• Root density influenced by genetics
• Root distribution / depth influenced by the soil
• For root growth to occur root growth pressure (turgour) > soil
strength
• Root types have different functions
• Woody = transport, anchorage, storage of carbs & nutrients
• Fine laterals = water and nutrient absorption
• Ability to function changes with age
• N & P uptake, respiration declining with age
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Root observation
• Rooting depth and extent
• Patterns and distribution of root growth
• Root location (within horizons, between cracks, along
compacted zones)
• Stunting, galling, knotting, lesions, discolouration
• Taking samples, washing & examining for symptoms
• Differences between rootstocks
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Aeration – drainage & water movement
• Waterlogging / Perching
• Root growth
• Colour indicators
– Overall soil colour (iron oxides)
– Mottling – depth, extent & colouration (buckshot)
– Gleying
• Smell
Permeability (cm/hr) on different textured soils
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Permeability (cm/hr)
20
15
10
5
0
Sand
Sandy
loam
Silt loam
Clay loam Silty clay
Clay
Texture
Landon J R - Booker Tropical Soil Manual
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WELL
DRAINED
MODERATELY
WELL
DRAINED
IMPERFECTLY
DRAINED
PALE
COLOURS
(BLEACHED)
Leached &
Imperfectly
drained
Well
Drained
Well
drained
• Soil has no
mottling or
yellowy grey
colours
within 90cm
of the soil
surface
Moderately well
drained
VARIABLE
DRAINAGE
IMPERFECTLY
DRAINED
Imperfectly
drained
DEPTH TO
POOR
DRAINAGE
Poorly drained
Poorly - very poorly
drained
• Mottling occurs to the soil
Moderately
well
drained
• Soil has
mottling or
yellowy grey
colours
within 6090cm of the
soil surface
VERY POORLY
DRAINED
HIGH CLAY
CONTENT
BLEACHED
IMPERFECTLY
DRAINED
POORLY
DRAINED
Imperfectly drained
• Soil has a bleached A horizon
• Soil has mottling or yellowy grey colours
within 30-60cm of the soil surface
surface
•The water table is within
30cm of the surface at some
time during the year
•The soil is dominated by
grey, pale, green or blue
colours.
• Undecomposed organic
matter occurs as a thatch on
the top of the soil
0 cm
30 cm
60 cm
90 cm+
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Ideal soil
• Soils are very heterogeneous at all scales
– Nutrient, water, aeration, soil strength, microbial profiles
etc can vary within mm’s
• Ideal soil
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Infiltration rate
= > 500mm/day (~ 20mm/ hr)
Total available water = 100-150mm
Penetration resistance = <2 MPa
Waterlogging
= < 1 day of saturation per rainfall
pH(CaCl2)
= 5.5 – 8.0
EC (dS/m)
=<2
Lanyon et al (2004)The effect of soil properties on vine performance. CSIRO Land & Water
http://www.clw.csiro.au/publications/technical2004/tr34-04.pdf
Take home messages – key points
• Don’t forget about what is going on at depth in your
soil – things change both externally & internally
• Root and subsoil examination is beneficial and
relatively easy
• Management – jury out on active remediation (+/-) –
do your own research specific to your
circumstances
• Adaptation to & zonal management of vineyard
differences can lead to more even production
• Don’t ask a kiwi sheep farmer difficult questions
about grapevine management – Particularly while
he is in a hole on a wet day!
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