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Entering into the Era Crop Rotation Strategy of Wheat: Wheat:
Green Manure will divide the 2400 ha farm into three areas of
800 hectares of which:
- 800ha is to be green manured
- 800ha is wheat after the green manure, and
- 800 ha is wheat following wheat.
Green Manure
The paddocks that are due to be green manured are sown to lupin/oats
on light to medium country or sown to peas/oats on heavier clay
country. Any paddocks that have a good weed burden are left alone,
as the weeds will provide sufficient biomass for a good green
manure. In the initial years of a green manuring programme some
fertiliser may be required to ensure sufficient biomass is grown
for the programme to be effective. The green manure crops can
be sown in late April but if the season breaks late, they can
be sown dry.
A top-dressing of 500kg/ha of lime mix, 100kg/ha of Era Phos and
50kg/ha of minerals is applied to the green manure. The lime mix
consists of limestone and gypsum. Applying the lime mix, Era Phos
and minerals in the green manure phase allows more time for these
materials to break down in the soil and halves the area of the
summer spreading program. The application of 100g/ha Era Phos
supplies enough P for the following wheat crops, which will reduce
down the tube fertiliser requirements in the long term. The minerals
drive the activity of the soil organisms, which in turn drive
the nutrient cycling. The lime mix provides plant available calcium,
improves soil structure and reduces soil acidity.
The green manure crops are sprayed off with glyphosate at 1 litre/ha
and then ploughed into the soil. The timing of the spraying is
determined by when ryegrass is setting viable seed. Spraying before
any new seed is set reduces the amount of weeds in the following
year and reduces the herbicide bill. Some carryover of ryegrass
seed in the second wheat crop is manageable, as the following
green manure crop will deliver a total kill of all weeds including
new ryegrass plants. When ploughing the green manure crop into
the soil, every effort is made to prepare a good seedbed so that
additional ploughing is not required and rough paddocks are avoided.
A coil packer is recommended.
No work is required once the green manure has been ploughed in.
No work is required except perhaps some spraying out of summer
weeds.
Wheat After Green Manuring
If the green manure stage left a good seedbed, no additional working
will be required. At the onset of initial rains a good germination
of weeds can be expected due to the soil disturbance caused by
ploughing in the green manure. After consecutive green manures
the weed burden and amount of viable seed will be reduced because
the fungal/bacteria ratios will have changed to allow plants other
than weeds to dominate. For the first wheat crop following the
first green manuring programme, the herbicide programme should
consist of a single knockdown spray followed by some pre-emergent
if necessary. Over time only a knockdown should be required. Because
of changes in soil structure, moisture from the first rains will
be able to soak deeper into the soil than previously possible.
This allows seeding deeper into moisture in dry years. In the
early years of using the Era Rotation strategy some down the tube
fertiliser may still be needed but if the green manure crop is
successful then no down the tube fertiliser or top-dressed nitrogen
should be necessary.
In the initial stages some post seeding spraying and fertiliser
application may be needed but this will be reduced and eventually
eliminated.
Preparations are made for ploughing in the wheat stubble as quickly
as possible after harvesting by having the necessary materials
on hand.
As soon as possible after harvest has been completed, the stubbles
are top-dressed with 500kg/ha of lime mix and 60kg/ha of Era Phos,
then sprayed with 10-20 units of nitrogen and 8 litres/ha of Stubble
Mulcher, then ploughed in dry. This process prepares the seed
bed for the next season, allows the stubbles to breakdown as soon
as moisture from summer rains becomes available, and incorporates
the lime mix and Era Phos into the soil prior to seeding. Wind
erosion is not of concern (except for the lightest soils) as some
stubble is left on top of the soil and prevents the wind from
getting a hold. Some summer weeds may need spraying out.
Wheat After Wheat
After the previous wheat crop stubble has been ploughed into the
soil, the seedbed is already prepared so the soil is ready for
seeding as soon as the time is right for the wheat variety. Any
rain in April sinks in deeper than normal and if conditions are
dry in May then seeding into the subsoil moisture can occur. No
down the tube fertiliser or top-dressed nitrogen is needed if
the initial green manuring has been successful and the previous
stubble has broken sown. At certain times, some additional fertiliser
may be needed as determined by soil food web tests and soil tests.
In the initial stages some post seeding spraying and fertiliser
application may be needed but this will be reduced and eventually
eliminated.
No action is required.
As the next crop is the green manure crop no action is required.
The stubble is left where it is along with any weeds that may
grow until it is time to seed the green manure crop.
General Benefits
of the Era Rotation Strategy
- The green manuring and stubble mulching greatly
accelerate improvement in soil structure and soil
fertility leading to higher yield potentials within
a lower cost structure.
- For green manuring and stubble mulching programmes
that are carried out after harvest, the seedbed
is already prepared for the break of the next season
so that the farmer is ready to seed whenever the
first rains fall.
- The top-dressing requirement for fertiliser and
workload is split over summer time and wintertime,
which leads to better cash flow and work load management.
- Time and cost of spraying weeds can be halved
within the first three years and reduced further
in the long term
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It should be noted that the amount of rainfall over the summer
determines the success of the stubble mulching and green manuring
programmes to reduce application rates of down the tube fertiliser
and herbicides for the following crop. In years of no summer rain
some fertiliser and chemical weed control will be needed. However,
once cropping areas have had numerous stubble mulches and green
manures, the years of no summer rain will not have the same impact
as the number of soil organisms are already very high.
Farm Profitability
Farm profitability is increased through achieving greater yields
from improved soil structure and fertility, which in turn reduces
the cost of planting the crop and the overheads relative to the
wheat crop value. Wheat is the most profitable cash crop available
to WA farmers and the Era Rotation allows a greater percentage
of the farm to be planted to wheat without the need for other
crops such as canola and lupins which have been used to provide
disease control or nitrogen. Similarly there is no need to run
sheep to provide weed control but animals can be a part of another
rotation strategy.
Risk Profile
The overall amount of risk can be reduced in the Era Rotation
Strategy as the soil improvements gained from green manuring and
stubble mulching reduce the traditional risk factors associated
with farming. The traditional risk factors are divided into the
seasonal factors and the market factors. Seasonal factors include
lack of rain, too much rain at the wrong time, frost events and
disease/pests. Market risks are mainly associated with the commodity
pricing.
Cropping in wheat reduces the hazards from lack
of winter rainfall, as wheat is the most drought tolerant crop
in WA. Further, there is more control over seeding the crop in
May/June on minimal rainfall as the seedbed is already prepared
and seeding is able to commence with as little as 30-50 points
of rain. Too much rain can still be a problem at harvest time
but waterlogging during the year will be reduced due to soil structure
improvements. Frost events still need to be managed properly but
the overall frost risk is reduced as the improved soil structure
enables crops to uptake high levels of soluble calcium, which
reduces plant susceptibility to frost events.
The main market risk is in a long-term price drop
in wheat. One safeguard against this is the ability to switch
from wheat into other cereals such as oats or barley if the prices
for the latter are high. However, the main financial protection
against low prices comes from maintaining low costs of production.
A profitable system, which protects against low prices, is central
to the Era Rotation Strategy.
Another advantage is crop expenditure is spread
over the year rather than all at one time allowing more control
over budget outlays relative to the season and price outlooks.
Farm Sustainability
The most pressing farm sustainability issues at present are herbicide
resistance, collapsing soil structure and fertility, water table
related problems, soil acidity and in some instances wind erosion.
The risk of herbicide resistance is dramatically
reduced within the Era Rotation Strategy. Green manuring using
a double knock down provides a total weed kill every three years
and reduces weed seed numbers to a manageable level. Also by increasing
the amount of residue returned to the soil and increasing soil
organism numbers, the germination and vigour of weeds is reduced.
Collapsing soil structure and low soil fertility
are easily improved by green manuring and stubble mulching in
conjunction with regular applications of calcium as these problems
are usually caused by lack of calcium and low numbers of soil
organisms.
Water table problems are usually caused by poor
water use efficiency. In some instances a total farm programme
may be required to tackle water table problems. A total farm programme
would involve drainage systems and a short-term stint of deep-rooted
plants. But by improving soil structure and water holding capacity
of the soil, the water use efficiency is increased which improves
crop yields and reduces the volume of water reaching the water
table
Soil acidity reduces crop yields and prevents the development
of better soil microbiology. Generally soil pH levels below 4.5
(Calcium Chloride) reduce wheat yields and soil pH levels below
5.5 prevent optimum functioning of soil organisms. The Era Rotation
Strategy recommends 1t/ha of a lime mix every three years, which
over a 5-10 year period will increase the soil pH and calcium
levels closer to the optimum levels. The target soil pH range
is between 6 and 7.
Wind erosion normally occurs on pasture paddocks
that have been grazed too heavily or on paddocks that have been
worked up early and have then dried out. Provided that enough
material is returned to the soil when green manuring or stubble
mulching, the risk of paddocks blowing in strong winds is negligible.
The material that still remains on top provides enough cover to
prevent the wind from taking hold of the soil.
Within 2-3 years of the implementation of the Era
Rotation Strategy major improvements in the soil structure and
soil biology are normally observed. Soil improvement is the key
to long-term sustainability.
Herbicide Usage
When using a green manure and stubble mulching program the amount
of herbicide used is reduced significantly. As the volume of material
incorporated into the soil increases, the volume of soil organisms
also increases which will alter the type of weeds that will dominate
relative to the crop. Some of the lower succession weeds such
as brome and barley grass will begin to disappear quite quickly.
Herbicide requirement for the wheat crop should fall to a knockdown
and some pre-emergent spray, and in some cases only a knockdown.
In years of low summer rainfall, closer to normal herbicide practices
will be necessary as there will be little breakdown of the stubbles
and the green manure residues. Accordingly, the herbicide bill
may vary from year to year, but implementing the Era Rotation
Strategy over the long term will reduce the herbicide costs.
Fertiliser Usage and Nutrient
Removal
The fertiliser use will change to reflect the materials needed
for soil structure improvement, soil organism food sources, and
replacement for the nutrients that the wheat crops remove. Understanding
the relationship between the nutrients applied and the nutrients
used by the crop is critical to profitable sustainable farming.
Although the fertiliser dollars will not change relative to current
practices, the different allocation of the fertiliser dollars
will produce higher yielding crops and greater soil improvements.
The nutrients removed in a three-year rotation of
GreenManure: Wheat: Wheat with both wheat crops yielding 2.5t/ha
with protein levels of 10% are:
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Nitrogen
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100kg |
Sulphur |
10kg |
Copper |
20g |
| Phosphorus |
15kg |
Calcium |
2kg |
Zinc |
100g |
| Potassium |
20kg |
Magnesium |
7kg |
Manganese |
225g |
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Nitrogen is the nutrient with the largest volume
removed. Two crops each of 2.5t/ha at 10% protein will remove
100kg/ha of nitrogen. Although this is a lot of nitrogen, a successful
green manure with good legume content is capable of replacing
this amount of nitrogen. A green manure crop with good legume
content yielding 5t/ha of dry matter will supply 150kg/ha of nitrogen
of which a good proportion is newly fixed nitrogen. In addition,
as the number of soil organism’s increase, more nitrogen
is fixed by free-living nitrogen fixing organisms. Successful
green manuring and improved soil fertility will greatly reduce
and even possibly eliminate the need for applied nitrogen to the
crops. In the initial stages the crop or the green manure may
require some nitrogen but only until sufficient plant material
has been broken down to increase humus levels.
Phosphorus will be mainly supplied by Era Phos and
is applied before the green manure and also before stubble mulching.
Over the three-year rotation a total of 160kg/ha of Era Phos is
recommended which will supply 18 kg of P and reinoculate the soil
with fungal organisms. The Era Phos applications will slowly build
the P level in the soil. In addition further P will be released
from the soil as the number of organisms increase. The key to
improving P nutrition is to increase the amount of P held within
soil organisms. This prevents leaching and lockup of P, which
is the main problem associated with the use of conventional P
fertilisers.
A large amount of potassium is required to grow
a large amount of biomass but relatively small amounts are carted
off with the grain. Potassium may be required on some of the lighter
soils and this can be achieved using potassium sulphate down the
tube when seeding the crop. Further potassium will be released
from the soil when ploughing due to mineralisation. Potassium
will not be an issue on many heavier and loamy soils.
Other nutrients may be needed in the initial stages
such as trace elements but as the Era Rotation Strategy develops
soil structures and increases the number of soil organisms, general
nutrient availability will be much higher. Nutrient recycling
within the soil will also be greatly improved as the increased
organism numbers will reduce leaching and lockup of plant nutrients.
A rotation of a green manure crop followed by two successive wheat
crops provides the best result for many growers in terms of farm
profitability and farm sustainability. On farm results are achieved
quickly and are typically exciting. The implementation of a farm
management technique such as the Era Rotation Strategy normally
requires an offset disc for the green manuring and stubble mulching.
However, in the initial stages many farmers are making do with
one way ploughs or are hiring off-set discs before making a decision
to purchase. For farmers with a long-term sheep enterprise, implementation
of a rotation like this can be seen as difficult but in most cases
it is a matter of looking at separating out the pasture and cropping
paddocks to achieve the best results.
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