module 12
Cropping systems management
Objectives
At the end of this module, you will:
- understand the ways to manipulate a crop to make it more competitive against weeds
- be able list more competitive and less competitive crops
- be able to describe at least three characteristics of more competitive wheat crops
- understand the advantages and disadvantages of varying crop sowing patterns and sowing times
Module Outline
- Introduction
- Crop and pasture rotations
- Use of crop competition
- Summary
- References and further reading
Introduction
A crop or pasture can be managed to make it grow better than the weeds within it. The management factors which can be manipulated include the:
- crop species or cultivar planted
- seeding rate used
- time of sowing and
- use of fertilizer
An understanding of weed population dynamics and ecology in relation to management tactics is essential for effective control of weeds. There has been little research into improved management of crops specifically for weed control since the 1970s; however, the advent of widespread resistance of weeds to herbicides in Australia (see Module 16) has renewed interest in management of crops as a tool for weed control.
The principles relating to this are the same in both crops and pastures. In the annual cropping system, the influence of management will be greater than in perennial pastures where insect or disease could have greater impact. Similarly, the replanting of competitive native species to areas where weeds of native ecosystems have been controlled, may aid in reducing re-invasion (see Module 17c). In the present discussion most reference will be to crop/ weed systems.
Crop and pasture rotations
Crop rotations have been traditionally used throughout Australia for the management of plant diseases. Such rotations are a well-established part of farm planning; however, rotations can also be used to enhance weed management. Rotations between different crops will discourage different weed species in different parts of the rotation. The following reading discusses how crop rotations can be used to enhance weed control.
The reading also considers how rotations to pastures can be
used to control weeds. You should note the tremendous diversity of possible
rotations. The choice of rotation will be influenced by numerous factors including
the availability of crop varieties adapted to particular soil and climate types.
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Use of crop competition
A major change in thinking regarding weed control in Australian cropping systems is the use of increased crop competition to reduce the impact and population growth of weeds. The following reading covers the latest ideas regarding the use of crop competition for weed management. You should note that competition might be enhanced in a number of ways, by choice of crop species, choice of crop cultivar, increased seeding rate, or by improved crop agronomy.
The reading also discusses the impact that alteration of sowing date can have on weed numbers. This discussion only focuses on the advantages that might accrue from delaying sowing. It should be pointed out that increased crop competition against weeds could also occur on some occasions through earlier sowing of crops. For example, the ability of canola to emerge and shade out later emerging weeds can be exploited by early or dry sowing in some circumstances.
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Summary
Management of the environment to favour growth of the crop rather than the weed can reduce the impact of weeds on crops (and pastures). However, a sound understanding of the population dynamics and ecology of the weed species is required. Some tactics that may be useful are: competitive crop species; competitive cultivars; increased seeding rate; delayed sowing; and optimal fertiliser application.
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References and further reading
Cousens, RG & Mortimer, M 1996, Dynamics of weed populations, Cambridge University Press, Cambridge, UK, pp. 169-216.
Di Tomaso, JM 1995, ‘Approaches for improving crop competitiveness through the manipulation of fertilizer strategies’, Weed Science, vol. 43, pp. 491-497.
Donald, CM & Hamblin, J 1976, ‘The biological yield and harvest index of cereals as agronomic and plant breeding criteria’, Advances in Agronomy, vol. 28, pp. 361-402.
King, W & Priest, S 1999, ‘Is fertiliser the best herbicide? - The effect of fertilisation on weed competition in pastures’, in AC Bishop, M Boersma and CD Barnes, (eds) Twelfth Australian Weeds Conference Papers and Proceedings, Tasmanian Weed Society, Devonport, Australia, pp. 170-173.
Lemerle, D, Verbeek, B & Coombes, NE 1996, ‘Interaction between wheat (Triticum aestivum) and diclofop to reduce the cost of annual ryegrass (Lolium rigidum) control’, Weed Science, vol. 44, pp. 634-639.
Lemerle, D, Verbeek, B & Orchard, B 2001, ‘Ranking the ability of wheat varieties to compete with Lolium rigidum’, Weed Research, vol. 41, pp. 197-209.
Medd, RW 1987, ‘Weed management on arable lands’, PS Cornish & JE Pratley, (eds.) in Tillage - New Directions in Australian Agriculture, Inkata Press, Melbourne, Australia, pp. 222-259.
Peltzer, S 1999, ‘Increased crop density reduces weed seed production without increasing screenings’, in AC Bishop, M Boersma and CD Barnes, (eds.) Twelfth Australian Weeds Conference Papers and Proceedings, Tasmanian Weed Society, Devonport, Australia, pp. 510-512.
Powles, SB & Matthews, JM 1996, ‘Integrated weed management for the control of herbicide resistant annual ryegrass (Lolium rigidum)’, Second International Weed Control Congress, pp. 407-414.
Tollenaar, M, Dibo, AA, Aguilera, A, Weise, SF, and Swanton, CJ 1994, ‘Effect of crop density on weed interference in maize’, Agronomy Journal, vol. 86, pp. 591-595.
Zimdahl, RL 1980, ‘Weed – Crop Competition’, IPPC, Corvallis USA, pp.117-124.
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Self assessmentDo you know:
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