Mechanical management of weeds - Ecological Management of Agricultural Weeds - page 139

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Mechanical management of weeds

Introduction

Physical removal of weeds by soil disturbance prior to planting, and
by hoeing and hand-weeding during crop growth are undoubtedly the oldest
forms of agricultural weed management. Farmers and agricultural equip-
ment manufacturers continue to develop this ancient tradition of mechanical
weed control through the refinement of hand tools and the invention of new
tillage and weeding machinery. The purpose of this chapter is to explore the
ways in which tillage before crop planting and mechanical weed control
methods after planting interact with the ecology of weeds, and to use that
understanding to suggest strategies for weed management.
Tillage and cultivation affect weeds in three distinct ways. First, they
uproot, dismember, and bury growing weeds and dormant perennating
organs. Second, they change the soil environment in ways that can promote
germination and establishment of weeds or, less commonly, inhibit germina-
tion and establishment. Third, they move weed seeds vertically and horizon-
tally, and this affects the probability that seedlings emerge, survive, and
compete with the crop.The second of these effects was discussed in Chapter 2.
The first and third are addressed in this chapter.
Each of the tools used for tillage and cultivation disturbs the soil in a
unique way. In particular, tools vary with respect to their working depth and
the degree to which they invert the soil column, break up soil aggregates, and
shake weed roots free from the soil. A general principle underlying this
chapter is that the impact of tillage or cultivation on a species depends on the interaction
between the nature of the soil disturbance and the life history characteristics of the weed .
The size, position, and physiology of shoots and underground organs have a
large influence on the weed's ability to survive a particular type of distur-
bance. Moreover, the size, longevity, and germination characteristics of seeds

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