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Warm Season Cropping in the southern cropping zone of Australia

N.S. Wilhelm

South Australian Research and Development Institute, Glen Osmond, South Australia.

ABSTRACT

Warm Season Cropping is the concept of growing summer crops in the cropping belt of southern Australia. These crops include grain sorghum, forage sorghum, corn, safflower, sunflower, millet, cotton and chickpeas. These crops are sown in spring to mature in late summer/autumn. The idea is to introduce these crops into current rotations as a regular phase of the rotation, not as an opportunity crop that is only sown following a wet harvest. They can be used to diversify rotations, provide breaks to current crop types, improve water use efficiency of current systems and compete with summer weeds. Their agronomy is centred around three fundamental principles; wide row spacings (up to 1 metre with skips), stubble retention with zero tillage and paddock preparation to ensure full soil profiles of water at seeding.

KEY WORDS

Summer crops, rotations, sustainability, cropping systems, water use efficiency, break crops.

What is warm season cropping?

Warm season cropping is the concept of growing summer crops in the cropping belt of southern Australia.

The idea was first promoted in Western Australia by Prof. Dwayne Beck of South Dakota University as a radical method to improve diversity in rotations and increase water usage in current systems; changes which are vital to cropping systems if herbicide resistant weeds are going to be managed, dryland salinity halted and reversed, and input costs reduced. This concept is receiving increasing attention across southern Australia because of the urgent need to increase the profitability and sustainability of current farming systems.

The crops being currently investigated include grain sorghum, forage sorghum, corn, safflower, sunflower, millet, cotton and chickpeas. These crops are sown in spring to mature in late summer/autumn. The concept is to introduce these crops into current rotations as a regular phase of the rotation, not as an opportunity crop that is only sown following a wet harvest. They can be used to diversify rotations, provide breaks to current crop types, improve water use efficiency of current systems and compete with summer weeds.

Their agronomy is centred around three fundamental principles; wide row spacings (up to 1 metre with skips), stubble retention with zero tillage and paddock preparation to ensure full soil profiles of water at seeding.

Why use warm season cropping?

The concept of warm season cropping is being considered because our current cropping systems (based entirely on annual winter-growing crop and pastures) are in jeopardy due to a range of pressures; agronomic, environmental and financial. For example:

  • Current cropping systems are not environmentally sustainable. Our efforts to improve them may be too slow and too small to improve their condition in time (and perhaps will never make them sustainable).
  • Despite a reputation for being the driest continent in the world, some of our major sustainability issues relate to too much water (partly due to a disrupted water balance from clearance of native perennial vegetation) eg. dryland salinity, transient water logging in winter, soil acidity from leaching of nitrates.
  • Herbicide resistant weeds and increasing pressure from summer weeds are serious threats to long term profitability.
  • Most current cropping systems have poor levels of water use efficiency and low profitability.

For these reasons, there needs to be a radical change to current cropping systems to improve water use efficiency, to provide new tools for combating weeds and to lift overall productivity (and hence profitability). Introduction of summer crops into the system is one such radical option.

What does warm season cropping offer?

Introduction of summer crops offers the following advantages to cropping systems in southern Australia:

  • Summer crops may not need to produce their own cash profit to justify their place in a rotation: beneficial effects on water balances, increased weed control etc. are sufficient reasons to try them.
  • Many summer crops have deeper and more aggressive root systems, which may access water in the profile not currently used by our winter crops and pastures. This feature is essential if they are to survive and produce in our relatively dry summers and provide many positive environmental impacts (eg. reduction of recharge into water tables, recycling of nutrients "lost" deep in soil profiles, reduction of winter waterlogging, increases of organic matter levels deeper in the profile, improvement of structure below surface layers with root channels, drier conditions and elevated organic matter).
  • They offer totally new options for controlling weeds in winter crops, especially herbicide resistant weeds (eg. shifting the growing season to one which winter weeds are not adapted to).
  • They act as totally new rotation options for breaking disease and pest cycles in winter crops (which in turn can act as disease and pest cycle breakers for summer crops).
  • Farms with both winter and summer crops would have more balanced work loads, so that extreme pressures at peak periods will be reduced and smaller capital investments may be adequate (eg. if you have less hectares to crop at any one time, a smaller plant may suffice). Cash flows may be more even, risks can be spread.
  • Summer crops compete strongly with summer weeds.
  • Summer crops eliminate bare soil conditions in summer (reducing the risk of wind and water erosion).
  • Summer crops are established crops in the world market so their general agronomy is well known, their breeding programs are well developed and markets already exist.
  • As annuals, they offer several of the benefits of lucerne but are more flexible (paddock is not committed to a single crop for 3-6 yrs).
  • They may increase soil flora and fauna diversity to alleviate “problem” pests in winter crops like rhizoctonia, CCN, Pratylenchus.

How should summer crops be grown?

Warm season cropping as a concept is NOT opportunity cropping after a wet harvest or because it was so wet in winter that September/October is the earliest opportunity to seed; it is a dedicated cropping system combining summer and winter crops in a logical but flexible rotation. The rotations would almost certainly comprise phases of summer and winter crops, sequenced in such a way to achieve specific targets of weed control (with low usage of selective herbicides), disease breaks and profits. Precision seeding with no tilling, minimal soil disturbance, wide row spacings and full stubble retention are essential ingredients for successful crop establishment and productivity.

Paddocks can be prepared in a number of ways, depending on paddock history and rainfall zones;

  • In low rainfall districts, paddocks can be kept clean with a chemical fallow until September, then the summer crop is seeded into a full profile of water,
  • A hay crop (seeded or volunteer) can be cut and then the summer crop seeded into the (killed) residues,
  • A green manure or cover crop can be sprayed out and then the summer crop seeded into the (killed) residues,
  • An early winter crop can be harvested and then the summer crop seeded into the stubble.

Obviously, the latter three options are higher risk (with respect to water supply and/or input costs), so varying establishment options would be an important management step.

Summer crops are grown on wide row spacings. The most likely arrangement is a skip row or double skip row configuration; the crop is seeded in rows nominally one metre apart but every third row (or third and fourth rows for double skips) is not seeded. The wide gaps between paired rows (two or three metres wide) act as water reservoirs for the crop to finish off on, but do not act as weed nurseries because of zero till establishment, stubble retention, and inter-row herbicide spraying is possible.

Will summer crops grow in southern AUSTRALIA?

Some farmers in the marginal areas of New South Wales and Queensland are achieving grain yields with sorghum of up to 18, (but regularly 12) kg/ha/mm moisture (moisture is the total of growing season rainfall and stored soil water at seeding) using agronomic packages which include wide row spacings, zero tillage and stubble retention. In southern Australia, these figures suggest that grain yields with sorghum of up to 4.6 t/ha and sunflower of up to 2.7 t/ha are possible with average rainfalls in typical locations of the southern cropping zone (see table 1 for some theoretical examples drawn from South Australian sites).

Table 1. Estimated grain yields for sorghum and sunflowers on a range of soil types and rainfall zones in the cropping zone of South Australia. Sorghum yields are estimated from yield=12 kg/ha * (mm stored water at seeding + growing season rainfall, mm). Sunflower yields are calculated to be 60% of sorghum yields under the same conditions.

Location

Soil profile

Average rainfall, Oct-Feb ( mm)

Depth of root zone (cm)

Max stored watera (mm)

Grain yield of sorghum (kg/ha)

Grain yield of sunflower (kg/ha)

Clare

Grey clay

173

140

209

4584

2750

Red brown earth

90

133

3672

2203

Keith

Sand over clay

142

120

153

3540

2124

Maitland

Sand over clay

132

120

153

3420

2052

Red brown earth

90

133

3180

1908

Mallee loam

95

132

3168

1901

Loxton

Sand over clay

114

120

153

3204

1922

Mallee loam

95

132

2952

1771

Minnipa

Mallee loam

97

95

132

2748

1649

a Plant available water in the theoretical root zone for summer crops

However, the figures in table 1 assume that there are no restrictions of root growth throughout the listed soil profiles. This assumption may be severely tested in profiles that have high levels of sodicity, salinity, boron or very low levels of fertility, all of which are common in cropping profiles of southern Australia. However, observations in Western Australia are that where summer weeds grow, these warm season crops will also grow through boron toxic and sodic sub-soils (Wayne Smith, pers comm). These summer weeds may therefore be indicators for soils that are also suitable for growing warm season crops.

Field trials are currently under way in Western Australia, South Australia and Victoria to test the performance of a range of summer crops under local conditions using different agronomic packages.

Contacts for more information

Nigel Wilhelm
Sustainable Farming Systems, SARDI
PMB 2 Glen Osmond South Australia 5064
08 8303-9353 work
08 8303-9385 fax
0407 185-501 mobile
wilhelm.nigel@saugov.sa.gov.au

Angie Roe
Farm Focus Consulting
Box 321 Northam Western Australia 6401
08 9622-5095 work
08 9622-7153 fax

farfocus@avon.net.au

Wayne Smith
Agronomic Acumen
PO Box 831 Albany Western Australia 6331
08 9842-1267 work
08 9842-1964 fax
0428 188-479 mobile
wsmith@agronomy.com.au

Adam Davies
Area Sales Manager, Pioneer Hi-bred Int Inc.

08 8395-5311 work
08 8395-5322 fax
0408 807-809 mobile
daviesa@phibred.com.au

Robert Amin
Seed Distributors Pty Ltd
6 Rosberg Rd Wingfield South Australia 5013
08 8359-1922 work
08 8359-1422 fax
0418 816-555 mobile

Sarah Walton
Territory Manager, Pacific Seeds Pty Ltd

03 5229-0579 work
03 5229-7605 fax
0417 756-151 mobile
sarah_walton@pacseeds.com.au

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