Weeds and the soil environment - Ecological Management of Agricultural Weeds - page 210

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Weeds and the soil environment

Introduction

One of the distinguishing characteristics of terrestrial plants is that
they spend a significant portion of their lives unable to travel farther than
they can grow. As a consequence of the sessile, fixed root habit, the resource
environment in which plants grow and reproduce is a very local phenomenon
and interactions among neighboring plants are common (Harper, 1977, p. 4).
The sessile habit makes it possible to suppress weeds through manipulations
of soil conditions.
Given the similarity of most terrestrial plant species in their requirements
for sunlight, water, and nutrients, it is not surprising that weeds compete
with crops for resources and reduce crop yields.Conversely,crop plants exert a
large competitive effect on associated weeds (see Chapter 6). A key insight
from ecology, however, is that outcomes of competitive interactions between
plants are highly dependent on environmental conditions, especially soil-
related factors.As Harper (1977,p.369) noted,“there is a very extensive litera-
ture in which it is demonstrated repeatedly that the balance between a pair of
species in mixture is changed by the addition of a particular nutrient, altera-
tion of the pH, change in the level of the water table, application of water
stress or of shading.”
Ecological studies have also revealed that plant abundance and distribu-
tion are affected by the availability of appropriate sites for germination and
establishment (Grubb,1977).Because plant species differ in their recruitment
responses to soil conditions (Harper, 1977, pp. 111-47), manipulations of soil
chemical, physical, and biological characteristics can lead to higher or lower
densities of particular species even before competitive interactions begin.
To date, relatively little research has focused on weed management
through manipulations of soil conditions other than herbicide application.

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