Gypsum application and deep
ripping for vineyard development
Alfred Cass & Associates
1700 Maggie Avenue, Calistoga, CA 94515, USA
USA: Phone 707 942 6384; Mobile 707 529 7408; USA: Fax 707 942 1503
Australia: Mobile +61 41 781 0025
The reason for improving and maintaining optimum soil structure is to
optimise water, nutrient and air availability to vines by making the soil
more porous, softer and more penetrable by roots. The spin off from this
is usually more uniform vineyards that can be managed more easily with
better control of berry ripening, improved productivity and berry quality
and more assured sustainability.
The main tools available for improving soil structure are:
- deep tillage to disrupt hard soil,
- addition of organic matter to stabilise soil aggregates near the surface,
- addition of gypsum to stabilise deeper aggregates created by deep
- use of minimum tillage and avoiding repeated, annual disturbance of
- covering the soil surface at all times by growing perennial, fibrous-rooted
cover crops controlled by mowing and/or herbicide application.
These notes briefly describe the use of these techniques
Gypsum, rather than other forms of calcium, is most commonly used to stabilse
soil aggregates because it is readily available, relatively cheap, easily
handled and can be used on most soil types. The main issues relating to
use of gypsum are:
- properties of the various types,
- deciding on when gypsum is required and when not,
- the amount of gypsum to apply,
- the method and timing of application.
Properties of gypsum
Soil properties which indicate a need for gypsum
Gypsum is a mineral: CaSO4-2H2O but it contains impurities. It is obtained
either by mining or as a by-product of the manufacture of concentrated
phosphate fertilisers and hydrofluoric acid. Gypsum quality depends on
two factors, purity (impurities include water, soil, limestone, salt,
fluoride, etc) and fineness. Ideally purity should be 14 to 16 % sulfur
(S) and more than 80 % should pass through a 2 mm sieve.
Gypsum should be applied to soil if one or more of these conditions are
present in soil:
- soil with more than 5% exchangeable sodium (ESP) on the clays, or
saturation extract sodium adsorption (SAR) greater than 6 or 1:5 soil:
water extract SAR greater than 3 (sodic soil),
- where calcium : magnesium ratios are less than 2 (soil is magnesic),
- where the saturation extract electrical conductivity is approaching
or greater than 2 dS/m or a 1:5 soil water extract is approaching or
greater than 0.2 dS/m for sandier soils and 0.3 dS/m for clayey soils
- soils that disperse in an aggregate stability test,
- subsoils that have massive, distinct blocky or columnar structure
that is firm, hard or rigid,
- subsoils that have pale or light gray, brown or yellow colours or
that show distinct or prominent mottles, particularly if the mottles
are pale or light gray, brown or yellow,
- soils which crust and/or set hard under the influence of rainfall
- cracking clay soils with large, widely spaced cracks or which seal
and crust after rainfall instead of self-mulching to form small (2 to
5 mm diameter) surface aggregates.
For gypsum to act it has to dissolve in soil water. Dissolution rate is
determined by how much rain or irrigation water passes through the soil.
As a rule of thumb, between 100 and 500 mm (4 to 20 inches) of rain or
uniformly distributed irrigation water will be required to dissolve 1
t/ha (900 lb/acre) of applied gypsum, depending on fineness and efficiency
of incorporation. This means that application of 5 tonnes/ha (2 ton/acre)
of gypsum could take as long as 3 years to dissolve completely. For this
reason, in most situations, depending on soil conditions, it is not sensible
to apply more than 5 to 10 tonnes of gypsum (2 to 4 tons) at a time.
If more gypsum is required, establish an annual or biannual application
program of 1 to 2 t/ha (0.5 to 1 ton/acre) of gypsum, spread on the soil
surface in autumn (fall). Soils with poorly structured surface layers
(crusted, hard set, compacted, erodible, cracking), should be dealt with
in the same way. Winter rain will leach the gypsum into the soil.
Gypsum can also be dissolved in irrigation water and applied through
the irrigation system. This is an efficient means of application, but
requires finely milled gypsum and specially designed equipment to mix
the gypsum and water.
When and where to apply gypsum
Apply gypsum in autumn (fall) prior to winter rain, which will dissolve
it and carry it to depth. Dissolution of large amounts is greatly aided
by banding it on the deep rip line and ripping it into the soil. Some
gypsum will be carried down mechanically but more importantly, rainwater
following the preferential path of the rip line will dissolve it and move
it to depth. Disking it in will also improve dissolution rate.
Deep ripping of vineyard soils is necessary if there is either a physical
or a chemical root impediment within a depth of up to 1 m (40 inches).
Ripping will disrupt the physical barrier, soften the soil, and allow
roots to exploit the full depth to the limit of deep ripping. It will
also assist in placement of ameliorants such as lime or gypsum and creates
improved drainage for removal of salinity, sodium, or excess water. Available
soil water is also increased because:
- large, water and air storage pores are created at the expense of smaller
- many larger water transmission pores are created,
- the effective root depth for the vine is increased of softening the
- penetration of rain and irrigation water is improved.
These benefits will persist longer if gypsum is added to stabilise the
newly created pores and heavy wheel traffic is rigorously excluded from
the vicinity of the rip line.
What soils should be deep ripped?
Deep ripping is indicated if any one of the following factors is present
in the soil:
- hard sheet rock that is shallow (< 50 cm, < 20 inches deep)
and thin (< 30 cm, < 12 inches thick) and which overlies soft,
- porous, well drained material which, after ripping, will not have
more than about 50 % gravel to the lower depth of ripping,
- partially weathered rock within 800 mm (32 inches) of the surface,
particularly if a cemented pan is present and which, after ripping,
will not have more than 50 % gravel to the lower depth of ripping,
- saprolite within 800 mm (32 inches) of the surface, particularly if
a cemented pan is present,
- hard, fine or rubble carbonate layers within 800 mm (32 inches) of
- firm, hard or rigid, poorly structured peds (large blocky and prismatic
or massive) within 800 mm (32 inches) of the surface,
- previously compacted agricultural land with a penetration resistance
in excess of 2 MPa at field capacity water content within a depth of
800 mm (32 inches) of the surface,
- saline subsoil (ECse > 2 dS/m or EC1:5 greater than 0.3 for clays
and 0.2 for lighter textures) or sodic (ESP > 6 %, SARse > 6 or
SAR1:5 > 3) or acid (pHCaCl2 < 5) or alkaline (pHCaCl > 9)
(ameliorants need to be added before ripping),
- waterlogged soil where a drainage barrier can be identified within
a depth of 800 mm (32 inches) from the surface.
When to deep rip?
The correct subsoil moisture content is critically important for effective
deep ripping of clay-rich soils. Generally there are only two periods
of the year when this condition can be met: late autumn (sufficient rainfall
to moisten but not saturate subsoil) and late spring (sufficient drying
out but not desiccation of subsoil). Only at these times will the soil
fracture correctly and yield fine (<20 mm, < _ inch diameter) fragments
necessary for optimum root penetration. At other times of the year soil
moisture content is unlikely to be at a level for optimal results. In
summer the subsoil is too dry and clay-rich soil shatters, creating large
clods and fine dust. In winter soil remoulds and compacts because of the
plasticity of wet clay. Sandy, gravelly and rocky soils are less critically
dependent on water content because they tend to be fracture in a brittle
way even when quite wet.
The correct subsoil moisture content for deep ripping is the plastic
limit. This water content lies between field capacity and wilting point.
A sample of the subsoil should be tested by vigorously kneading a handful
of subsoil long enough to break down aggregates and form a ball. If a
ball can be formed it should be broken open and a pinch of soil taken
from the centre and rolled out on the palm of the hand to form a thread.
Shorten the thread if necessary to facilitate rolling. The diameter of
the thread that is obtainable from this procedure predicts what will happen
to the subsoil on ripping:
- If the subsoil rolls out into a thread that crumbles as it approaches
a diameter of 3 mm (1/8 inch), the water content is correct for optimal
results: tensile fracturing and maximum lift of the subsoil to yield
small clods, the majority not bigger than about 20 mm (3/4 inch) diameter,
and a minimum of fine dust.
- If the soil rolls into a thread smaller than 3 mm (1/8 inch) in diameter,
the soil is too wet for optimal fracturing and the subsoil will not
fracture laterally, the effect of ripping may be plastic failure leaving
narrow slots with the main body of subsoil intact and deposition of
large subsoil clods on the surface.
- If the subsoil cannot be worked into a ball that can be rolled into
a thread or if a coarse thread forms that crumbles well before it reaches
3 mm (1/8 mm), the soil is too dry for ripping and the result will be
brittle fracturing of the subsoil leaving many large clods in a matrix
of fine dust.
If gypsum is required for subsoil amelioration, broadcast half of the
gypsum on the surface during the autumn prior to ripping. Winter rain
will leach the gypsum into the soil, where, if it reaches the subsoil,
a degree of softening can be expected, and a better ripping product achieved.
If the soil is to be ripped in late spring, sow a cereal crop to stabilise
the soil through winter and use the winter rainfall. This will provide
the means to control soil wetness at the time of ripping in spring. If
ripping is done in autumn, and a year’s lead in time is not available,
apply up to 5 tonnes/ha (2 ton/acre) of the gypsum requirement on the
rip line and rip the gypsum into the soil. If the gypsum requirement is
over 5 tonnes/ha (2 ton/acre), broadcast the remainder onto the surface
and work it in during subsequent vineyard preparation.
How to deep rip
The depth of working is important for optimum results. Each ripper blade
has a critical working depth in hard soil, below which the blade will
not fracture the soil laterally, but compact it. Test a section of ripped
soil by digging a trench behind the ripper and examining the soil for:
- no compaction (penetration resistance << 2 MPa),
- correct size of clods (most < 20 mm, < _ inch) diameter),
- minimum amount of dust (most > 0.25 mm, 0.06 inch diameter),
- proper lateral fracturing to give a wide (> 1 m, 40 inches) fractured
zone at the soil surface.
- correct depth of ripping, (up to 1 m, 40 inches), depending on desired
root zone volume and subsoil conditions.
Do not proceed with ripping if all these factors are not correct. If
necessary raise the ripper working depth and rip on the same lines more
than once, going progressively deeper with each pass. Alternatively use
a tandem of ripper blades with the rear blades spaced immediately behind
the front ones but working deeper.
The shape of the ripper blade is important for correct fracturing of
subsoil material. Hard rock, weathered rock, and cemented pans require
a wingless blade with a point having a rake angle of at least 20O. Clay
subsoils require a winged blade (Figure 1) with a 90O point and angled
at 20O for maximum lateral fracturing and maximum lift. The rake angle
of 20O is critical. Tines with a greater rake angle will compact the soil
adjacent to and below the rip line. Tines with angles less than 20O will
not lift and shatter the subsoil. South African experience suggests that
a series of 20O wings spaced down the ripper tine is effective in diffusing
the boundaries of sharply layered soils ("Duplex" soils) without
undue mixing of horizons. The latter needs to be avoided if deep material
has an undesirable effect on shallower soil properties.
Figure 1: Optimum dimensions and rake angle of a winged
tine suitable for deep ripping clay and clay loam soils at the plastic
limit moisture content.
Direction of ripping and spacing of ripper tines depends on the aims
of ripping and the depth and extent of fracturing required. For complete
disruption of an impeding layer, the spacing of the tines must be 2/3
of the final depth of ripping. Ripping only on the row is a cost beneficial
way of establishing vines but will probably not create conditions for
lateral spread of the vine root system into the midrow. This may be an
important consideration in vineyards where irrigation water is limited
and reliance on rainfall storage great.
Recompaction of vineyards is a common occurrence because of the need
to traffic the midrow to prepare for planting, install trellis posts and
subsequently manage the vineyard. Ripping on the row and rigorously avoiding
trafficking the rip line provides an immediate optimum root environment
for the young vine and leaves available the option of ripping wheel tracks
after the vineyard is established.
Closely spaced ripping may preclude trafficability of the vineyard for
some time if wet conditions occur after ripping. Cross ripping at 90O
may also create conditions of excessive soil wetness. In general, the
direction of travel during ripping should be down slope to facilitate
natural drainage. If cross ripping is necessary, excessive wetness can
be reduced by cross ripping at 60O with the intersecting rip lines running
Other important points that need to be considered are:
- the power of the tractor or the depth of ripping must be such that
wheel or track slippage is minimised to prevent damage to surface soil
- the speed of travel should be slow, less that 5 km/h (3 miles/hour),
- use a section of railroad track dragged behind the ripper to smooth
the surface, not the tractor blade,
- avoid driving heavy machinery on the rip line.
Immediately after deep ripping the surface soil should be prepared for
sowing a cover crop and incorporating the remaining amendments, fertiliser
and on-row organic matter. At this time secondary wheel compaction can
be eliminated by using deep working tines behind the tractor wheels..
A set of tines (up to 300 mm, 12 inches deep) behind the wheels of heavy
tractors wheel will prevent further compaction. Do not use of a rotary
hoe to finish off land preparation, rather disking with the tractor wheels
straddling the rip line.
A cover crop should be sown immediately after ripping, particularly on
steep land. Generally, a grass or cereal cover crop is ideal for controlling
erosion and stabilising the beneficial soil structure created by ripping
and tillage. The cover crop should be controlled by coarse mowing rather
than fine slashing, to provide a durable surface mulch.