Objectives

At the end of this module, you will be able to:

• be able to describe the objectives of physical weed management
• be able to describe different tillage systems
• know the benefits and drawbacks of minimum tillage systems

Module Outline

• Introduction
• Objectives and types of tillage
• Other physical management methods
• Summary
• References and further reading

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Introduction

This module considers the issues related to the effects of physical weed control with an emphasis on tillage practices on weed management. It will become evident that no one tillage system is appropriate in all circumstances and some flexibility is needed. It is also important to appreciate that weeds comprise only one aspect of a complex of issues related to tillage that need to be considered, including soil conservation. The present discussion specifically focuses on the impact of tillage practices on weeds.

Objectives and types of tillage

Tillage is the disturbance of soil by mechanical means usually as a preparation for sowing of crops or pastures. There are many different implements used for tillage and each has a specific purpose:

• chisel plough
• disc plough
• mouldboard plough
• rotary hoe

The different types and objectives of tillage are outlined in the following reading. You should particularly note the historical aspects in the development of tillage systems in Australia. The generally light erodable soils of much of Australia have meant that tillage has reduced in intensity over the past two decades.

You should also note the effects that different types of tillage have on seed germination. For example shallow burial of annual ryegrass seed encourages germination, whereas burial of Vulpia seed inhibits germination. Therefore, different types of tillage can encourage and discourage different weed flora.

Reading "Tillage and other physical management methods" (pages 105-111) in Australian Weed Management Systems (click on each image for a larger view)

In addition to their effects on weed germination, different tillage implements have different soil disrupting characteristics. Such characteristics will influence the choice of tillage implement and how often tillage is undertaken.

The characteristics of four different tillage implements are described in Table 10.1.

Table 10.1. A comparison of various types of tillage instruments and their actions on soil (modified from Pratley 1988)

Action	Mouldboard plough	Disc plough	Chisel plough	Rotary hoe
Wear	Shares require replacement	Superior life	Points wear	Can be rapid
Movement of soil	Complete inversion	Partial inversion	Narrow furrows	Thoroughly mixes soil
Grinding of soil	Very little	Tendency	Little	Extensive
Shattering effect	Complete	Partial	Partial	Complete
Compacting effect	Considerable if soil too moist	Considerable if soil moist	Very little	Very considerable
Fineness produced	Very little	Considerable	Moderate	Very considerable
Surface trash	Well buried	Buries a large proportion	Left on surface	Buries a large proportion
Seedbed preparation	Requires secondary tillage	Ideal general cultivation	Ideal row crop cultivation	Makes soil fine in one operation
Control of weeds	Unsuited	Excellent	Can be excellent	Excellent

The effects of various tillage implements on soil and existing vegetation:

Tillage implement	Impact
Mouldboard		Turns over sod, which buries seed and weeds. However, the clods are fairly large and weed roots may not be destroyed allowing the weeds to re-grow.
Disc plough		Slicing action not only buries weeds, but also tends to break up roots
Chisel plough		Breaks up the soil into smaller particles to the depth of the ploughing operation. It will control small existing weeds effectively provided full soil disturbance is achieved.
Rotary hoe		Shatters the soil more and effectively handles existing weeds
Images adapted from Pratley (1988).

Other physical management methods

Other physical methods can be used to remove weeds. Some such as roguing are widely used for specific weeds. Others such as mulching are used widely in particular industries. The following reading discusses the use of several physical methods for weed control and points out the industries in which they are used. You will encounter a more detailed discussion of some of these methods in Module 17A.

Reading "Tillage and other physical management methods" (pages 112-119) in Australian Weed Management Systems (click on each image for a larger view)

Summary

Tillage remains one of the tools in weed management. Used wisely it can provide a very valuable option but it clearly can be counterproductive with the wrong species. In the past we have tended to be too dogmatic in our approach when flexibility is the appropriate strategy.

The impact of tillage relates to the:

• dormancy characteristics of the weed species
• effects on the vigour of the crop
• ability of weeds to regenerate from plant fragments
• ability to achieve timeliness of operations
• ability of the weed to survive surface environmental fluctuations
• ability of the weed to germinate and emerge from depth

Go to Activity 10-1

References and further reading

Amor, RL 1985, ‘Seasonal emergence of weeds typically occurring in the Victorian cereal belt’, Plant Protection Quarterly, vol. 1, pp. 18-20.

Cheam, AH 1987, ‘Longevity of Bromus diandrus Roth. seed in soil at three sites in Western Australia’, Plant Protection Quarterly, vol. 2, pp. 137-139.

Cornish, PS & Pratley, JE, (eds) 1987, Tillage - New Directions in Australian Agriculture, Inkata Press, Melbourne, Vic.

Cuthbertson, EG 1967, ‘Skeleton weed - distribution and control’, NSW Department of Agriculture Bulletin 68.

Cuthbertson, EG, Leys, AR & McMaster, G 1976, ‘Silverleaf nightshade - a potential threat to agriculture’, Agricultural Gazette of NSW, vol. 87, pp. 11-13.

Dillon, SP & Forcella, F 1984, ‘Germination, emergence, vegetative growth and flowering of two silvergrasses, Vulpia bromoides and V. myuros’, Australian Journal of Botany, vol. 32, pp. 165-175.

Gramshaw, D & Stern, WR 1977, ‘Survival of annual ryegrass (Lolium rigidum Gaud.) seed in a Mediterranean type environment. II. Effects of short-term burial on persistence of viable seed’, Australian Journal of Agricultural Research, vol. 28, pp. 93-101.

Kloot, PM 1987, ‘Influence of environmental factors on the germination and establishment of barley grass (Hordeum glaucum) and annual ryegrass (Lolium rigidum)’, Australian Journal of Experimental Agriculture, vol. 27, pp. 525- 532.

Medd, RW 1987, ‘Weed Management on Arable Lands’, in PS Cornish & JE Pratley, (eds), Tillage - New Directions in Australian Agriculture, Inkata Press, Melbourne. pp. 222-259.

Moss, SR 1979, ‘The influence of tillage and method of straw disposal on the survival and growth of black-grass, Alopecurus myosuroides, and its control by chlortoluron and isoproturon’, Annals of Applied Biology, vol. 91, pp. 91-100.

Pratley, JE, (ed.) 1988, Principles of Field Crop Production, 2nd edn, Sydney University Press, Sydney.

Pratley, JE 1995, ‘Long term investigations of the effects of tillage practices on crop production at Wagga Wagga, New South Wales’, Australian Journal of Experimental Agriculture, vol. 35, pp. 885-892.

Reeves, TG and Smith, IS 1975, ‘Pasture management and cultural methods for the control of annual ryegrass (Lolium rigidum) in wheat’, Australian Journal of Experimental Agriculture and Animal Husbandry, vol. 15, pp. 527-530.

Wells, GJ 1970, ‘Skeleton weed in the Victorian mallee. 2. Effects of legumes on soil fertility, subsequent wheat crops and weed population’, Australian Journal of Experimental Agriculture and Animal Husbandry, vol. 10, pp. 622-629.

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Self assessment Do you know: how to describe the objectives of physical seed management how to describe different tillage systems the benefits and drawbacks of minimum tillage systems